src/librustc_lint/builtin.rs

   1 //! Lints in the Rust compiler.
   2 //!
   3 //! This contains lints which can feasibly be implemented as their own
   4 //! AST visitor. Also see `rustc::lint::builtin`, which contains the
   5 //! definitions of lints that are emitted directly inside the main
   6 //! compiler.
   7 //!
   8 //! To add a new lint to rustc, declare it here using `declare_lint!()`.
   9 //! Then add code to emit the new lint in the appropriate circumstances.
  10 //! You can do that in an existing `LintPass` if it makes sense, or in a
  11 //! new `LintPass`, or using `Session::add_lint` elsewhere in the
  12 //! compiler. Only do the latter if the check can't be written cleanly as a
  13 //! `LintPass` (also, note that such lints will need to be defined in
  14 //! `rustc::lint::builtin`, not here).
  15 //!
  16 //! If you define a new `EarlyLintPass`, you will also need to add it to the
  17 //! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
  18 //! `lib.rs`. Use the former for unit-like structs and the latter for structs
  19 //! with a `pub fn new()`.
  20 //!
  21 //! If you define a new `LateLintPass`, you will also need to add it to the
  22 //! `late_lint_methods!` invocation in `lib.rs`.
  23
  24 use std::fmt::Write;
  25
  26 use rustc::hir::def::{Res, DefKind};
  27 use rustc::hir::def_id::DefId;
  28 use rustc::ty::{self, Ty, TyCtxt, layout::VariantIdx};
  29 use rustc::{lint, util};
  30 use rustc::lint::FutureIncompatibleInfo;
  31 use hir::Node;
  32 use util::nodemap::HirIdSet;
  33 use lint::{LateContext, LintContext, LintArray};
  34 use lint::{LintPass, LateLintPass, EarlyLintPass, EarlyContext};
  35
  36 use rustc::util::nodemap::FxHashSet;
  37 use rustc_feature::{AttributeGate, AttributeTemplate, AttributeType, deprecated_attributes};
  38 use rustc_feature::Stability;
  39
  40 use syntax::tokenstream::{TokenTree, TokenStream};
  41 use syntax::ast::{self, Expr};
  42 use syntax::ptr::P;
  43 use syntax::attr::{self, HasAttrs};
  44 use syntax::source_map::Spanned;
  45 use syntax::edition::Edition;
  46 use syntax_pos::{BytePos, Span};
  47 use syntax::symbol::{Symbol, kw, sym};
  48 use syntax::errors::{Applicability, DiagnosticBuilder};
  49 use syntax::print::pprust::{self, expr_to_string};
  50 use syntax::visit::FnKind;
  51
  52 use rustc::hir::{self, GenericParamKind, PatKind};
  53
  54 use crate::nonstandard_style::{MethodLateContext, method_context};
  55
  56 use log::debug;
  57
  58 // hardwired lints from librustc
  59 pub use lint::builtin::*;
  60
  61 declare_lint! {
  62     WHILE_TRUE,
  63     Warn,
  64     "suggest using `loop { }` instead of `while true { }`"
  65 }
  66
  67 declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
  68
  69 /// Traverse through any amount of parenthesis and return the first non-parens expression.
  70 fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
  71     while let ast::ExprKind::Paren(sub) = &expr.kind {
  72         expr = sub;
  73     }
  74     expr
  75 }
  76
  77 impl EarlyLintPass for WhileTrue {
  78     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  79         if let ast::ExprKind::While(cond, ..) = &e.kind {
  80             if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
  81                 if let ast::LitKind::Bool(true) = lit.kind {
  82                     if !lit.span.from_expansion() {
  83                         let msg = "denote infinite loops with `loop { ... }`";
  84                         let condition_span = cx.sess.source_map().def_span(e.span);
  85                         cx.struct_span_lint(WHILE_TRUE, condition_span, msg)
  86                             .span_suggestion_short(
  87                                 condition_span,
  88                                 "use `loop`",
  89                                 "loop".to_owned(),
  90                                 Applicability::MachineApplicable
  91                             )
  92                             .emit();
  93                     }
  94                 }
  95             }
  96         }
  97     }
  98 }
  99
 100 declare_lint! {
 101     BOX_POINTERS,
 102     Allow,
 103     "use of owned (Box type) heap memory"
 104 }
 105
 106 declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
 107
 108 impl BoxPointers {
 109     fn check_heap_type(&self, cx: &LateContext<'_, '_>, span: Span, ty: Ty<'_>) {
 110         for leaf_ty in ty.walk() {
 111             if leaf_ty.is_box() {
 112                 let m = format!("type uses owned (Box type) pointers: {}", ty);
 113                 cx.span_lint(BOX_POINTERS, span, &m);
 114             }
 115         }
 116     }
 117 }
 118
 119 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoxPointers {
 120     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
 121         match it.kind {
 122             hir::ItemKind::Fn(..) |
 123             hir::ItemKind::TyAlias(..) |
 124             hir::ItemKind::Enum(..) |
 125             hir::ItemKind::Struct(..) |
 126             hir::ItemKind::Union(..) => {
 127                 let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 128                 self.check_heap_type(cx, it.span, cx.tcx.type_of(def_id))
 129             }
 130             _ => ()
 131         }
 132
 133         // If it's a struct, we also have to check the fields' types
 134         match it.kind {
 135             hir::ItemKind::Struct(ref struct_def, _) |
 136             hir::ItemKind::Union(ref struct_def, _) => {
 137                 for struct_field in struct_def.fields() {
 138                     let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
 139                     self.check_heap_type(cx, struct_field.span,
 140                                          cx.tcx.type_of(def_id));
 141                 }
 142             }
 143             _ => (),
 144         }
 145     }
 146
 147     fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr) {
 148         let ty = cx.tables.node_type(e.hir_id);
 149         self.check_heap_type(cx, e.span, ty);
 150     }
 151 }
 152
 153 declare_lint! {
 154     NON_SHORTHAND_FIELD_PATTERNS,
 155     Warn,
 156     "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
 157 }
 158
 159 declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
 160
 161 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NonShorthandFieldPatterns {
 162     fn check_pat(&mut self, cx: &LateContext<'_, '_>, pat: &hir::Pat) {
 163         if let PatKind::Struct(ref qpath, ref field_pats, _) = pat.kind {
 164             let variant = cx.tables.pat_ty(pat).ty_adt_def()
 165                                    .expect("struct pattern type is not an ADT")
 166                                    .variant_of_res(cx.tables.qpath_res(qpath, pat.hir_id));
 167             for fieldpat in field_pats {
 168                 if fieldpat.is_shorthand {
 169                     continue;
 170                 }
 171                 if fieldpat.span.from_expansion() {
 172                     // Don't lint if this is a macro expansion: macro authors
 173                     // shouldn't have to worry about this kind of style issue
 174                     // (Issue #49588)
 175                     continue;
 176                 }
 177                 if let PatKind::Binding(_, _, ident, None) = fieldpat.pat.kind {
 178                     if cx.tcx.find_field_index(ident, &variant) ==
 179                        Some(cx.tcx.field_index(fieldpat.hir_id, cx.tables)) {
 180                         let mut err = cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS,
 181                                      fieldpat.span,
 182                                      &format!("the `{}:` in this pattern is redundant", ident));
 183                         let subspan = cx.tcx.sess.source_map().span_through_char(fieldpat.span,
 184                                                                                  ':');
 185                         err.span_suggestion_short(
 186                             subspan,
 187                             "remove this",
 188                             ident.to_string(),
 189                             Applicability::MachineApplicable
 190                         );
 191                         err.emit();
 192                     }
 193                 }
 194             }
 195         }
 196     }
 197 }
 198
 199 declare_lint! {
 200     UNSAFE_CODE,
 201     Allow,
 202     "usage of `unsafe` code"
 203 }
 204
 205 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
 206
 207 impl UnsafeCode {
 208     fn report_unsafe(&self, cx: &EarlyContext<'_>, span: Span, desc: &'static str) {
 209         // This comes from a macro that has `#[allow_internal_unsafe]`.
 210         if span.allows_unsafe() {
 211             return;
 212         }
 213
 214         cx.span_lint(UNSAFE_CODE, span, desc);
 215     }
 216 }
 217
 218 impl EarlyLintPass for UnsafeCode {
 219     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 220         if attr.check_name(sym::allow_internal_unsafe) {
 221             self.report_unsafe(cx, attr.span, "`allow_internal_unsafe` allows defining \
 222                                                macros using unsafe without triggering \
 223                                                the `unsafe_code` lint at their call site");
 224         }
 225     }
 226
 227     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
 228         if let ast::ExprKind::Block(ref blk, _) = e.kind {
 229             // Don't warn about generated blocks; that'll just pollute the output.
 230             if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
 231                 self.report_unsafe(cx, blk.span, "usage of an `unsafe` block");
 232             }
 233         }
 234     }
 235
 236     fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
 237         match it.kind {
 238             ast::ItemKind::Trait(_, ast::Unsafety::Unsafe, ..) => {
 239                 self.report_unsafe(cx, it.span, "declaration of an `unsafe` trait")
 240             }
 241
 242             ast::ItemKind::Impl(ast::Unsafety::Unsafe, ..) => {
 243                 self.report_unsafe(cx, it.span, "implementation of an `unsafe` trait")
 244             }
 245
 246             _ => return,
 247         }
 248     }
 249
 250     fn check_fn(&mut self,
 251                 cx: &EarlyContext<'_>,
 252                 fk: FnKind<'_>,
 253                 _: &ast::FnDecl,
 254                 span: Span,
 255                 _: ast::NodeId) {
 256         match fk {
 257             FnKind::ItemFn(_, ast::FnHeader { unsafety: ast::Unsafety::Unsafe, .. }, ..) => {
 258                 self.report_unsafe(cx, span, "declaration of an `unsafe` function")
 259             }
 260
 261             FnKind::Method(_, sig, ..) => {
 262                 if sig.header.unsafety == ast::Unsafety::Unsafe {
 263                     self.report_unsafe(cx, span, "implementation of an `unsafe` method")
 264                 }
 265             }
 266
 267             _ => (),
 268         }
 269     }
 270
 271     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, item: &ast::TraitItem) {
 272         if let ast::TraitItemKind::Method(ref sig, None) = item.kind {
 273             if sig.header.unsafety == ast::Unsafety::Unsafe {
 274                 self.report_unsafe(cx, item.span, "declaration of an `unsafe` method")
 275             }
 276         }
 277     }
 278 }
 279
 280 declare_lint! {
 281     pub MISSING_DOCS,
 282     Allow,
 283     "detects missing documentation for public members",
 284     report_in_external_macro
 285 }
 286
 287 pub struct MissingDoc {
 288     /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
 289     doc_hidden_stack: Vec<bool>,
 290
 291     /// Private traits or trait items that leaked through. Don't check their methods.
 292     private_traits: FxHashSet<hir::HirId>,
 293 }
 294
 295 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
 296
 297 fn has_doc(attr: &ast::Attribute) -> bool {
 298     if !attr.check_name(sym::doc) {
 299         return false;
 300     }
 301
 302     if attr.is_value_str() {
 303         return true;
 304     }
 305
 306     if let Some(list) = attr.meta_item_list() {
 307         for meta in list {
 308             if meta.check_name(sym::include) || meta.check_name(sym::hidden) {
 309                 return true;
 310             }
 311         }
 312     }
 313
 314     false
 315 }
 316
 317 impl MissingDoc {
 318     pub fn new() -> MissingDoc {
 319         MissingDoc {
 320             doc_hidden_stack: vec![false],
 321             private_traits: FxHashSet::default(),
 322         }
 323     }
 324
 325     fn doc_hidden(&self) -> bool {
 326         *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
 327     }
 328
 329     fn check_missing_docs_attrs(&self,
 330                                 cx: &LateContext<'_, '_>,
 331                                 id: Option<hir::HirId>,
 332                                 attrs: &[ast::Attribute],
 333                                 sp: Span,
 334                                 desc: &'static str) {
 335         // If we're building a test harness, then warning about
 336         // documentation is probably not really relevant right now.
 337         if cx.sess().opts.test {
 338             return;
 339         }
 340
 341         // `#[doc(hidden)]` disables missing_docs check.
 342         if self.doc_hidden() {
 343             return;
 344         }
 345
 346         // Only check publicly-visible items, using the result from the privacy pass.
 347         // It's an option so the crate root can also use this function (it doesn't
 348         // have a `NodeId`).
 349         if let Some(id) = id {
 350             if !cx.access_levels.is_exported(id) {
 351                 return;
 352             }
 353         }
 354
 355         let has_doc = attrs.iter().any(|a| has_doc(a));
 356         if !has_doc {
 357             cx.span_lint(MISSING_DOCS,
 358                          cx.tcx.sess.source_map().def_span(sp),
 359                          &format!("missing documentation for {}", desc));
 360         }
 361     }
 362 }
 363
 364 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDoc {
 365     fn enter_lint_attrs(&mut self, _: &LateContext<'_, '_>, attrs: &[ast::Attribute]) {
 366         let doc_hidden = self.doc_hidden() ||
 367                          attrs.iter().any(|attr| {
 368             attr.check_name(sym::doc) &&
 369             match attr.meta_item_list() {
 370                 None => false,
 371                 Some(l) => attr::list_contains_name(&l, sym::hidden),
 372             }
 373         });
 374         self.doc_hidden_stack.push(doc_hidden);
 375     }
 376
 377     fn exit_lint_attrs(&mut self, _: &LateContext<'_, '_>, _attrs: &[ast::Attribute]) {
 378         self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
 379     }
 380
 381     fn check_crate(&mut self, cx: &LateContext<'_, '_>, krate: &hir::Crate) {
 382         self.check_missing_docs_attrs(cx, None, &krate.attrs, krate.span, "crate");
 383
 384         for macro_def in &krate.exported_macros {
 385             let has_doc = macro_def.attrs.iter().any(|a| has_doc(a));
 386             if !has_doc {
 387                 cx.span_lint(MISSING_DOCS,
 388                              cx.tcx.sess.source_map().def_span(macro_def.span),
 389                              "missing documentation for macro");
 390             }
 391         }
 392     }
 393
 394     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
 395         let desc = match it.kind {
 396             hir::ItemKind::Fn(..) => "a function",
 397             hir::ItemKind::Mod(..) => "a module",
 398             hir::ItemKind::Enum(..) => "an enum",
 399             hir::ItemKind::Struct(..) => "a struct",
 400             hir::ItemKind::Union(..) => "a union",
 401             hir::ItemKind::Trait(.., ref trait_item_refs) => {
 402                 // Issue #11592: traits are always considered exported, even when private.
 403                 if let hir::VisibilityKind::Inherited = it.vis.node {
 404                     self.private_traits.insert(it.hir_id);
 405                     for trait_item_ref in trait_item_refs {
 406                         self.private_traits.insert(trait_item_ref.id.hir_id);
 407                     }
 408                     return;
 409                 }
 410                 "a trait"
 411             }
 412             hir::ItemKind::TyAlias(..) => "a type alias",
 413             hir::ItemKind::Impl(.., Some(ref trait_ref), _, ref impl_item_refs) => {
 414                 // If the trait is private, add the impl items to `private_traits` so they don't get
 415                 // reported for missing docs.
 416                 let real_trait = trait_ref.path.res.def_id();
 417                 if let Some(hir_id) = cx.tcx.hir().as_local_hir_id(real_trait) {
 418                     match cx.tcx.hir().find(hir_id) {
 419                         Some(Node::Item(item)) => {
 420                             if let hir::VisibilityKind::Inherited = item.vis.node {
 421                                 for impl_item_ref in impl_item_refs {
 422                                     self.private_traits.insert(impl_item_ref.id.hir_id);
 423                                 }
 424                             }
 425                         }
 426                         _ => {}
 427                     }
 428                 }
 429                 return;
 430             }
 431             hir::ItemKind::Const(..) => "a constant",
 432             hir::ItemKind::Static(..) => "a static",
 433             _ => return,
 434         };
 435
 436         self.check_missing_docs_attrs(cx, Some(it.hir_id), &it.attrs, it.span, desc);
 437     }
 438
 439     fn check_trait_item(&mut self, cx: &LateContext<'_, '_>, trait_item: &hir::TraitItem) {
 440         if self.private_traits.contains(&trait_item.hir_id) {
 441             return;
 442         }
 443
 444         let desc = match trait_item.kind {
 445             hir::TraitItemKind::Const(..) => "an associated constant",
 446             hir::TraitItemKind::Method(..) => "a trait method",
 447             hir::TraitItemKind::Type(..) => "an associated type",
 448         };
 449
 450         self.check_missing_docs_attrs(cx,
 451                                       Some(trait_item.hir_id),
 452                                       &trait_item.attrs,
 453                                       trait_item.span,
 454                                       desc);
 455     }
 456
 457     fn check_impl_item(&mut self, cx: &LateContext<'_, '_>, impl_item: &hir::ImplItem) {
 458         // If the method is an impl for a trait, don't doc.
 459         if method_context(cx, impl_item.hir_id) == MethodLateContext::TraitImpl {
 460             return;
 461         }
 462
 463         let desc = match impl_item.kind {
 464             hir::ImplItemKind::Const(..) => "an associated constant",
 465             hir::ImplItemKind::Method(..) => "a method",
 466             hir::ImplItemKind::TyAlias(_) => "an associated type",
 467             hir::ImplItemKind::OpaqueTy(_) => "an associated `impl Trait` type",
 468         };
 469         self.check_missing_docs_attrs(cx,
 470                                       Some(impl_item.hir_id),
 471                                       &impl_item.attrs,
 472                                       impl_item.span,
 473                                       desc);
 474     }
 475
 476     fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, sf: &hir::StructField) {
 477         if !sf.is_positional() {
 478             self.check_missing_docs_attrs(cx,
 479                                           Some(sf.hir_id),
 480                                           &sf.attrs,
 481                                           sf.span,
 482                                           "a struct field")
 483         }
 484     }
 485
 486     fn check_variant(&mut self, cx: &LateContext<'_, '_>, v: &hir::Variant) {
 487         self.check_missing_docs_attrs(cx,
 488                                       Some(v.id),
 489                                       &v.attrs,
 490                                       v.span,
 491                                       "a variant");
 492     }
 493 }
 494
 495 declare_lint! {
 496     pub MISSING_COPY_IMPLEMENTATIONS,
 497     Allow,
 498     "detects potentially-forgotten implementations of `Copy`"
 499 }
 500
 501 declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
 502
 503 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingCopyImplementations {
 504     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
 505         if !cx.access_levels.is_reachable(item.hir_id) {
 506             return;
 507         }
 508         let (def, ty) = match item.kind {
 509             hir::ItemKind::Struct(_, ref ast_generics) => {
 510                 if !ast_generics.params.is_empty() {
 511                     return;
 512                 }
 513                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 514                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 515             }
 516             hir::ItemKind::Union(_, ref ast_generics) => {
 517                 if !ast_generics.params.is_empty() {
 518                     return;
 519                 }
 520                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 521                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 522             }
 523             hir::ItemKind::Enum(_, ref ast_generics) => {
 524                 if !ast_generics.params.is_empty() {
 525                     return;
 526                 }
 527                 let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
 528                 (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
 529             }
 530             _ => return,
 531         };
 532         if def.has_dtor(cx.tcx) {
 533             return;
 534         }
 535         let param_env = ty::ParamEnv::empty();
 536         if ty.is_copy_modulo_regions(cx.tcx, param_env, item.span) {
 537             return;
 538         }
 539         if param_env.can_type_implement_copy(cx.tcx, ty).is_ok() {
 540             cx.span_lint(MISSING_COPY_IMPLEMENTATIONS,
 541                          item.span,
 542                          "type could implement `Copy`; consider adding `impl \
 543                           Copy`")
 544         }
 545     }
 546 }
 547
 548 declare_lint! {
 549     MISSING_DEBUG_IMPLEMENTATIONS,
 550     Allow,
 551     "detects missing implementations of fmt::Debug"
 552 }
 553
 554 #[derive(Default)]
 555 pub struct MissingDebugImplementations {
 556     impling_types: Option<HirIdSet>,
 557 }
 558
 559 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 560
 561 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDebugImplementations {
 562     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
 563         if !cx.access_levels.is_reachable(item.hir_id) {
 564             return;
 565         }
 566
 567         match item.kind {
 568             hir::ItemKind::Struct(..) |
 569             hir::ItemKind::Union(..) |
 570             hir::ItemKind::Enum(..) => {}
 571             _ => return,
 572         }
 573
 574         let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
 575             Some(debug) => debug,
 576             None => return,
 577         };
 578
 579         if self.impling_types.is_none() {
 580             let mut impls = HirIdSet::default();
 581             cx.tcx.for_each_impl(debug, |d| {
 582                 if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
 583                     if let Some(hir_id) = cx.tcx.hir().as_local_hir_id(ty_def.did) {
 584                         impls.insert(hir_id);
 585                     }
 586                 }
 587             });
 588
 589             self.impling_types = Some(impls);
 590             debug!("{:?}", self.impling_types);
 591         }
 592
 593         if !self.impling_types.as_ref().unwrap().contains(&item.hir_id) {
 594             cx.span_lint(MISSING_DEBUG_IMPLEMENTATIONS,
 595                          item.span,
 596                          "type does not implement `fmt::Debug`; consider adding `#[derive(Debug)]` \
 597                           or a manual implementation")
 598         }
 599     }
 600 }
 601
 602 declare_lint! {
 603     pub ANONYMOUS_PARAMETERS,
 604     Allow,
 605     "detects anonymous parameters",
 606     @future_incompatible = FutureIncompatibleInfo {
 607         reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
 608         edition: Some(Edition::Edition2018),
 609     };
 610 }
 611
 612 declare_lint_pass!(
 613     /// Checks for use of anonymous parameters (RFC 1685).
 614     AnonymousParameters => [ANONYMOUS_PARAMETERS]
 615 );
 616
 617 impl EarlyLintPass for AnonymousParameters {
 618     fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::TraitItem) {
 619         match it.kind {
 620             ast::TraitItemKind::Method(ref sig, _) => {
 621                 for arg in sig.decl.inputs.iter() {
 622                     match arg.pat.kind {
 623                         ast::PatKind::Ident(_, ident, None) => {
 624                             if ident.name == kw::Invalid {
 625                                 let ty_snip = cx
 626                                     .sess
 627                                     .source_map()
 628                                     .span_to_snippet(arg.ty.span);
 629
 630                                 let (ty_snip, appl) = if let Ok(snip) = ty_snip {
 631                                     (snip, Applicability::MachineApplicable)
 632                                 } else {
 633                                     ("<type>".to_owned(), Applicability::HasPlaceholders)
 634                                 };
 635
 636                                 cx.struct_span_lint(
 637                                     ANONYMOUS_PARAMETERS,
 638                                     arg.pat.span,
 639                                     "anonymous parameters are deprecated and will be \
 640                                      removed in the next edition."
 641                                 ).span_suggestion(
 642                                     arg.pat.span,
 643                                     "Try naming the parameter or explicitly \
 644                                     ignoring it",
 645                                     format!("_: {}", ty_snip),
 646                                     appl
 647                                 ).emit();
 648                             }
 649                         }
 650                         _ => (),
 651                     }
 652                 }
 653             },
 654             _ => (),
 655         }
 656     }
 657 }
 658
 659 /// Check for use of attributes which have been deprecated.
 660 #[derive(Clone)]
 661 pub struct DeprecatedAttr {
 662     // This is not free to compute, so we want to keep it around, rather than
 663     // compute it for every attribute.
 664     depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
 665 }
 666
 667 impl_lint_pass!(DeprecatedAttr => []);
 668
 669 impl DeprecatedAttr {
 670     pub fn new() -> DeprecatedAttr {
 671         DeprecatedAttr {
 672             depr_attrs: deprecated_attributes(),
 673         }
 674     }
 675 }
 676
 677 fn lint_deprecated_attr(
 678     cx: &EarlyContext<'_>,
 679     attr: &ast::Attribute,
 680     msg: &str,
 681     suggestion: Option<&str>,
 682 ) {
 683     cx.struct_span_lint(DEPRECATED, attr.span, &msg)
 684         .span_suggestion_short(
 685             attr.span,
 686             suggestion.unwrap_or("remove this attribute"),
 687             String::new(),
 688             Applicability::MachineApplicable
 689         )
 690         .emit();
 691 }
 692
 693 impl EarlyLintPass for DeprecatedAttr {
 694     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
 695         for &&(n, _, _, ref g) in &self.depr_attrs {
 696             if attr.ident().map(|ident| ident.name) == Some(n) {
 697                 if let &AttributeGate::Gated(Stability::Deprecated(link, suggestion),
 698                                              ref name,
 699                                              ref reason,
 700                                              _) = g {
 701                     let msg = format!("use of deprecated attribute `{}`: {}. See {}",
 702                                       name, reason, link);
 703                     lint_deprecated_attr(cx, attr, &msg, suggestion);
 704                 }
 705                 return;
 706             }
 707         }
 708         if attr.check_name(sym::no_start) || attr.check_name(sym::crate_id) {
 709             let path_str = pprust::path_to_string(&attr.get_normal_item().path);
 710             let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
 711             lint_deprecated_attr(cx, attr, &msg, None);
 712         }
 713     }
 714 }
 715
 716 declare_lint! {
 717     pub UNUSED_DOC_COMMENTS,
 718     Warn,
 719     "detects doc comments that aren't used by rustdoc"
 720 }
 721
 722 declare_lint_pass!(UnusedDocComment => [UNUSED_DOC_COMMENTS]);
 723
 724 impl UnusedDocComment {
 725     fn warn_if_doc(
 726         &self,
 727         cx: &EarlyContext<'_>,
 728         node_span: Span,
 729         node_kind: &str,
 730         is_macro_expansion: bool,
 731         attrs: &[ast::Attribute]
 732     ) {
 733         let mut attrs = attrs.into_iter().peekable();
 734
 735         // Accumulate a single span for sugared doc comments.
 736         let mut sugared_span: Option<Span> = None;
 737
 738         while let Some(attr) = attrs.next() {
 739             if attr.is_doc_comment() {
 740                 sugared_span = Some(
 741                     sugared_span.map_or_else(
 742                         || attr.span,
 743                         |span| span.with_hi(attr.span.hi()),
 744                     ),
 745                 );
 746             }
 747
 748             if attrs.peek().map(|next_attr| next_attr.is_doc_comment()).unwrap_or_default() {
 749                 continue;
 750             }
 751
 752             let span = sugared_span.take().unwrap_or_else(|| attr.span);
 753
 754             if attr.check_name(sym::doc) {
 755                 let mut err = cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, "unused doc comment");
 756
 757                 err.span_label(
 758                     node_span,
 759                     format!("rustdoc does not generate documentation for {}", node_kind)
 760                 );
 761
 762                 if is_macro_expansion {
 763                     err.help("to document an item produced by a macro, \
 764                               the macro must produce the documentation as part of its expansion");
 765                 }
 766
 767                 err.emit();
 768             }
 769         }
 770     }
 771 }
 772
 773 impl EarlyLintPass for UnusedDocComment {
 774     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
 775         if let ast::ItemKind::Mac(..) = item.kind {
 776             self.warn_if_doc(cx, item.span, "macro expansions", true, &item.attrs);
 777         }
 778     }
 779
 780     fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
 781         let (kind, is_macro_expansion) = match stmt.kind {
 782             ast::StmtKind::Local(..) => ("statements", false),
 783             ast::StmtKind::Item(..) => ("inner items", false),
 784             ast::StmtKind::Mac(..) => ("macro expansions", true),
 785             // expressions will be reported by `check_expr`.
 786             ast::StmtKind::Semi(..) |
 787             ast::StmtKind::Expr(..) => return,
 788         };
 789
 790         self.warn_if_doc(cx, stmt.span, kind, is_macro_expansion, stmt.kind.attrs());
 791     }
 792
 793     fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
 794         let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
 795         self.warn_if_doc(cx, arm_span, "match arms", false, &arm.attrs);
 796     }
 797
 798     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
 799         self.warn_if_doc(cx, expr.span, "expressions", false, &expr.attrs);
 800     }
 801 }
 802
 803 declare_lint! {
 804     NO_MANGLE_CONST_ITEMS,
 805     Deny,
 806     "const items will not have their symbols exported"
 807 }
 808
 809 declare_lint! {
 810     NO_MANGLE_GENERIC_ITEMS,
 811     Warn,
 812     "generic items must be mangled"
 813 }
 814
 815 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
 816
 817 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidNoMangleItems {
 818     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
 819         match it.kind {
 820             hir::ItemKind::Fn(.., ref generics, _) => {
 821                 if let Some(no_mangle_attr) = attr::find_by_name(&it.attrs, sym::no_mangle) {
 822                     for param in &generics.params {
 823                         match param.kind {
 824                             GenericParamKind::Lifetime { .. } => {}
 825                             GenericParamKind::Type { .. } |
 826                             GenericParamKind::Const { .. } => {
 827                                 let mut err = cx.struct_span_lint(
 828                                     NO_MANGLE_GENERIC_ITEMS,
 829                                     it.span,
 830                                     "functions generic over types or consts must be mangled",
 831                                 );
 832                                 err.span_suggestion_short(
 833                                     no_mangle_attr.span,
 834                                     "remove this attribute",
 835                                     String::new(),
 836                                     // Use of `#[no_mangle]` suggests FFI intent; correct
 837                                     // fix may be to monomorphize source by hand
 838                                     Applicability::MaybeIncorrect
 839                                 );
 840                                 err.emit();
 841                                 break;
 842                             }
 843                         }
 844                     }
 845                 }
 846             }
 847             hir::ItemKind::Const(..) => {
 848                 if attr::contains_name(&it.attrs, sym::no_mangle) {
 849                     // Const items do not refer to a particular location in memory, and therefore
 850                     // don't have anything to attach a symbol to
 851                     let msg = "const items should never be `#[no_mangle]`";
 852                     let mut err = cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, msg);
 853
 854                     // account for "pub const" (#45562)
 855                     let start = cx.tcx.sess.source_map().span_to_snippet(it.span)
 856                         .map(|snippet| snippet.find("const").unwrap_or(0))
 857                         .unwrap_or(0) as u32;
 858                     // `const` is 5 chars
 859                     let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
 860                     err.span_suggestion(
 861                         const_span,
 862                         "try a static value",
 863                         "pub static".to_owned(),
 864                         Applicability::MachineApplicable
 865                     );
 866                     err.emit();
 867                 }
 868             }
 869             _ => {}
 870         }
 871     }
 872 }
 873
 874 declare_lint! {
 875     MUTABLE_TRANSMUTES,
 876     Deny,
 877     "mutating transmuted &mut T from &T may cause undefined behavior"
 878 }
 879
 880 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
 881
 882 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutableTransmutes {
 883     fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &hir::Expr) {
 884         use rustc_target::spec::abi::Abi::RustIntrinsic;
 885
 886         let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
 887                    consider instead using an UnsafeCell";
 888         match get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (&ty1.kind, &ty2.kind)) {
 889             Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) => {
 890                 if to_mt == hir::Mutability::Mutable &&
 891                    from_mt == hir::Mutability::Immutable {
 892                     cx.span_lint(MUTABLE_TRANSMUTES, expr.span, msg);
 893                 }
 894             }
 895             _ => (),
 896         }
 897
 898         fn get_transmute_from_to<'a, 'tcx>
 899             (cx: &LateContext<'a, 'tcx>,
 900              expr: &hir::Expr)
 901              -> Option<(Ty<'tcx>, Ty<'tcx>)> {
 902             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
 903                 cx.tables.qpath_res(qpath, expr.hir_id)
 904             } else {
 905                 return None;
 906             };
 907             if let Res::Def(DefKind::Fn, did) = def {
 908                 if !def_id_is_transmute(cx, did) {
 909                     return None;
 910                 }
 911                 let sig = cx.tables.node_type(expr.hir_id).fn_sig(cx.tcx);
 912                 let from = sig.inputs().skip_binder()[0];
 913                 let to = *sig.output().skip_binder();
 914                 return Some((from, to));
 915             }
 916             None
 917         }
 918
 919         fn def_id_is_transmute(cx: &LateContext<'_, '_>, def_id: DefId) -> bool {
 920             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic &&
 921             cx.tcx.item_name(def_id) == sym::transmute
 922         }
 923     }
 924 }
 925
 926 declare_lint! {
 927     UNSTABLE_FEATURES,
 928     Allow,
 929     "enabling unstable features (deprecated. do not use)"
 930 }
 931
 932 declare_lint_pass!(
 933     /// Forbids using the `#[feature(...)]` attribute
 934     UnstableFeatures => [UNSTABLE_FEATURES]
 935 );
 936
 937 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnstableFeatures {
 938     fn check_attribute(&mut self, ctx: &LateContext<'_, '_>, attr: &ast::Attribute) {
 939         if attr.check_name(sym::feature) {
 940             if let Some(items) = attr.meta_item_list() {
 941                 for item in items {
 942                     ctx.span_lint(UNSTABLE_FEATURES, item.span(), "unstable feature");
 943                 }
 944             }
 945         }
 946     }
 947 }
 948
 949 declare_lint! {
 950     pub UNREACHABLE_PUB,
 951     Allow,
 952     "`pub` items not reachable from crate root"
 953 }
 954
 955 declare_lint_pass!(
 956     /// Lint for items marked `pub` that aren't reachable from other crates.
 957     UnreachablePub => [UNREACHABLE_PUB]
 958 );
 959
 960 impl UnreachablePub {
 961     fn perform_lint(&self, cx: &LateContext<'_, '_>, what: &str, id: hir::HirId,
 962                     vis: &hir::Visibility, span: Span, exportable: bool) {
 963         let mut applicability = Applicability::MachineApplicable;
 964         match vis.node {
 965             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
 966                 if span.from_expansion() {
 967                     applicability = Applicability::MaybeIncorrect;
 968                 }
 969                 let def_span = cx.tcx.sess.source_map().def_span(span);
 970                 let mut err = cx.struct_span_lint(UNREACHABLE_PUB, def_span,
 971                                                   &format!("unreachable `pub` {}", what));
 972                 let replacement = if cx.tcx.features().crate_visibility_modifier {
 973                     "crate"
 974                 } else {
 975                     "pub(crate)"
 976                 }.to_owned();
 977
 978                 err.span_suggestion(
 979                     vis.span,
 980                     "consider restricting its visibility",
 981                     replacement,
 982                     applicability,
 983                 );
 984                 if exportable {
 985                     err.help("or consider exporting it for use by other crates");
 986                 }
 987                 err.emit();
 988             },
 989             _ => {}
 990         }
 991     }
 992 }
 993
 994 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnreachablePub {
 995     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
 996         self.perform_lint(cx, "item", item.hir_id, &item.vis, item.span, true);
 997     }
 998
 999     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, foreign_item: &hir::ForeignItem) {
1000         self.perform_lint(cx, "item", foreign_item.hir_id, &foreign_item.vis,
1001                           foreign_item.span, true);
1002     }
1003
1004     fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, field: &hir::StructField) {
1005         self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
1006     }
1007
1008     fn check_impl_item(&mut self, cx: &LateContext<'_, '_>, impl_item: &hir::ImplItem) {
1009         self.perform_lint(cx, "item", impl_item.hir_id, &impl_item.vis, impl_item.span, false);
1010     }
1011 }
1012
1013 declare_lint! {
1014     TYPE_ALIAS_BOUNDS,
1015     Warn,
1016     "bounds in type aliases are not enforced"
1017 }
1018
1019 declare_lint_pass!(
1020     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1021     /// They are relevant when using associated types, but otherwise neither checked
1022     /// at definition site nor enforced at use site.
1023     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1024 );
1025
1026 impl TypeAliasBounds {
1027     fn is_type_variable_assoc(qpath: &hir::QPath) -> bool {
1028         match *qpath {
1029             hir::QPath::TypeRelative(ref ty, _) => {
1030                 // If this is a type variable, we found a `T::Assoc`.
1031                 match ty.kind {
1032                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1033                         match path.res {
1034                             Res::Def(DefKind::TyParam, _) => true,
1035                             _ => false
1036                         }
1037                     }
1038                     _ => false
1039                 }
1040             }
1041             hir::QPath::Resolved(..) => false,
1042         }
1043     }
1044
1045     fn suggest_changing_assoc_types(ty: &hir::Ty, err: &mut DiagnosticBuilder<'_>) {
1046         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1047         // bound.  Let's see if this type does that.
1048
1049         // We use a HIR visitor to walk the type.
1050         use rustc::hir::intravisit::{self, Visitor};
1051         struct WalkAssocTypes<'a, 'db> {
1052             err: &'a mut DiagnosticBuilder<'db>
1053         }
1054         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1055             fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'v>
1056             {
1057                 intravisit::NestedVisitorMap::None
1058             }
1059
1060             fn visit_qpath(&mut self, qpath: &'v hir::QPath, id: hir::HirId, span: Span) {
1061                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1062                     self.err.span_help(span,
1063                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1064                          associated types in type aliases");
1065                 }
1066                 intravisit::walk_qpath(self, qpath, id, span)
1067             }
1068         }
1069
1070         // Let's go for a walk!
1071         let mut visitor = WalkAssocTypes { err };
1072         visitor.visit_ty(ty);
1073     }
1074 }
1075
1076 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeAliasBounds {
1077     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
1078         let (ty, type_alias_generics) = match item.kind {
1079             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1080             _ => return,
1081         };
1082         let mut suggested_changing_assoc_types = false;
1083         // There must not be a where clause
1084         if !type_alias_generics.where_clause.predicates.is_empty() {
1085             let spans : Vec<_> = type_alias_generics.where_clause.predicates.iter()
1086                 .map(|pred| pred.span()).collect();
1087             let mut err = cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans,
1088                 "where clauses are not enforced in type aliases");
1089             err.span_suggestion(
1090                 type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
1091                 "the clause will not be checked when the type alias is used, and should be removed",
1092                 String::new(),
1093                 Applicability::MachineApplicable,
1094             );
1095             if !suggested_changing_assoc_types {
1096                 TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1097                 suggested_changing_assoc_types = true;
1098             }
1099             err.emit();
1100         }
1101         // The parameters must not have bounds
1102         for param in type_alias_generics.params.iter() {
1103             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1104             let suggestion = spans.iter().map(|sp| {
1105                 let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
1106                 (start.to(*sp), String::new())
1107             }).collect();
1108             if !spans.is_empty() {
1109                 let mut err = cx.struct_span_lint(
1110                     TYPE_ALIAS_BOUNDS,
1111                     spans,
1112                     "bounds on generic parameters are not enforced in type aliases",
1113                 );
1114                 let msg = "the bound will not be checked when the type alias is used, \
1115                            and should be removed";
1116                 err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
1117                 if !suggested_changing_assoc_types {
1118                     TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1119                     suggested_changing_assoc_types = true;
1120                 }
1121                 err.emit();
1122             }
1123         }
1124     }
1125 }
1126
1127 declare_lint_pass!(
1128     /// Lint constants that are erroneous.
1129     /// Without this lint, we might not get any diagnostic if the constant is
1130     /// unused within this crate, even though downstream crates can't use it
1131     /// without producing an error.
1132     UnusedBrokenConst => []
1133 );
1134
1135 fn check_const(cx: &LateContext<'_, '_>, body_id: hir::BodyId) {
1136     let def_id = cx.tcx.hir().body_owner_def_id(body_id);
1137     let param_env = if cx.tcx.is_static(def_id) {
1138         // Use the same param_env as `codegen_static_initializer`, to reuse the cache.
1139         ty::ParamEnv::reveal_all()
1140     } else {
1141         cx.tcx.param_env(def_id)
1142     };
1143     let cid = ::rustc::mir::interpret::GlobalId {
1144         instance: ty::Instance::mono(cx.tcx, def_id),
1145         promoted: None
1146     };
1147     // trigger the query once for all constants since that will already report the errors
1148     // FIXME: Use ensure here
1149     let _ = cx.tcx.const_eval(param_env.and(cid));
1150 }
1151
1152 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedBrokenConst {
1153     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
1154         match it.kind {
1155             hir::ItemKind::Const(_, body_id) => {
1156                 check_const(cx, body_id);
1157             },
1158             hir::ItemKind::Static(_, _, body_id) => {
1159                 check_const(cx, body_id);
1160             },
1161             _ => {},
1162         }
1163     }
1164 }
1165
1166 declare_lint! {
1167     TRIVIAL_BOUNDS,
1168     Warn,
1169     "these bounds don't depend on an type parameters"
1170 }
1171
1172 declare_lint_pass!(
1173     /// Lint for trait and lifetime bounds that don't depend on type parameters
1174     /// which either do nothing, or stop the item from being used.
1175     TrivialConstraints => [TRIVIAL_BOUNDS]
1176 );
1177
1178 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TrivialConstraints {
1179     fn check_item(
1180         &mut self,
1181         cx: &LateContext<'a, 'tcx>,
1182         item: &'tcx hir::Item,
1183     ) {
1184         use rustc::ty::fold::TypeFoldable;
1185         use rustc::ty::Predicate::*;
1186
1187         if cx.tcx.features().trivial_bounds {
1188             let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1189             let predicates = cx.tcx.predicates_of(def_id);
1190             for &(predicate, span) in predicates.predicates {
1191                 let predicate_kind_name = match predicate {
1192                     Trait(..) => "Trait",
1193                     TypeOutlives(..) |
1194                     RegionOutlives(..) => "Lifetime",
1195
1196                     // Ignore projections, as they can only be global
1197                     // if the trait bound is global
1198                     Projection(..) |
1199                     // Ignore bounds that a user can't type
1200                     WellFormed(..) |
1201                     ObjectSafe(..) |
1202                     ClosureKind(..) |
1203                     Subtype(..) |
1204                     ConstEvaluatable(..) => continue,
1205                 };
1206                 if predicate.is_global() {
1207                     cx.span_lint(
1208                         TRIVIAL_BOUNDS,
1209                         span,
1210                         &format!("{} bound {} does not depend on any type \
1211                                 or lifetime parameters", predicate_kind_name, predicate),
1212                     );
1213                 }
1214             }
1215         }
1216     }
1217 }
1218
1219 declare_lint_pass!(
1220     /// Does nothing as a lint pass, but registers some `Lint`s
1221     /// which are used by other parts of the compiler.
1222     SoftLints => [
1223         WHILE_TRUE,
1224         BOX_POINTERS,
1225         NON_SHORTHAND_FIELD_PATTERNS,
1226         UNSAFE_CODE,
1227         MISSING_DOCS,
1228         MISSING_COPY_IMPLEMENTATIONS,
1229         MISSING_DEBUG_IMPLEMENTATIONS,
1230         ANONYMOUS_PARAMETERS,
1231         UNUSED_DOC_COMMENTS,
1232         NO_MANGLE_CONST_ITEMS,
1233         NO_MANGLE_GENERIC_ITEMS,
1234         MUTABLE_TRANSMUTES,
1235         UNSTABLE_FEATURES,
1236         UNREACHABLE_PUB,
1237         TYPE_ALIAS_BOUNDS,
1238         TRIVIAL_BOUNDS
1239     ]
1240 );
1241
1242 declare_lint! {
1243     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1244     Warn,
1245     "`...` range patterns are deprecated"
1246 }
1247
1248 #[derive(Default)]
1249 pub struct EllipsisInclusiveRangePatterns {
1250     /// If `Some(_)`, suppress all subsequent pattern
1251     /// warnings for better diagnostics.
1252     node_id: Option<ast::NodeId>,
1253 }
1254
1255 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1256
1257 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1258     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1259         if self.node_id.is_some() {
1260             // Don't recursively warn about patterns inside range endpoints.
1261             return
1262         }
1263
1264         use self::ast::{PatKind, RangeEnd, RangeSyntax::DotDotDot};
1265
1266         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1267         /// corresponding to the ellipsis.
1268         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(&P<Expr>, &P<Expr>, Span)> {
1269             match &pat.kind {
1270                 PatKind::Range(a, b, Spanned { span, node: RangeEnd::Included(DotDotDot), .. }) => {
1271                     Some((a, b, *span))
1272                 }
1273                 _ => None,
1274             }
1275         }
1276
1277         let (parenthesise, endpoints) = match &pat.kind {
1278             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1279             _ => (false, matches_ellipsis_pat(pat)),
1280         };
1281
1282         if let Some((start, end, join)) = endpoints {
1283             let msg = "`...` range patterns are deprecated";
1284             let suggestion = "use `..=` for an inclusive range";
1285             if parenthesise {
1286                 self.node_id = Some(pat.id);
1287                 let mut err = cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, msg);
1288                 err.span_suggestion(
1289                     pat.span,
1290                     suggestion,
1291                     format!("&({}..={})", expr_to_string(&start), expr_to_string(&end)),
1292                     Applicability::MachineApplicable,
1293                 );
1294                 err.emit();
1295             } else {
1296                 let mut err = cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, msg);
1297                 err.span_suggestion_short(
1298                     join,
1299                     suggestion,
1300                     "..=".to_owned(),
1301                     Applicability::MachineApplicable,
1302                 );
1303                 err.emit();
1304             };
1305         }
1306     }
1307
1308     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1309         if let Some(node_id) = self.node_id {
1310             if pat.id == node_id {
1311                 self.node_id = None
1312             }
1313         }
1314     }
1315 }
1316
1317 declare_lint! {
1318     UNNAMEABLE_TEST_ITEMS,
1319     Warn,
1320     "detects an item that cannot be named being marked as `#[test_case]`",
1321     report_in_external_macro
1322 }
1323
1324 pub struct UnnameableTestItems {
1325     boundary: hir::HirId, // HirId of the item under which things are not nameable
1326     items_nameable: bool,
1327 }
1328
1329 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1330
1331 impl UnnameableTestItems {
1332     pub fn new() -> Self {
1333         Self {
1334             boundary: hir::DUMMY_HIR_ID,
1335             items_nameable: true
1336         }
1337     }
1338 }
1339
1340 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnameableTestItems {
1341     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
1342         if self.items_nameable {
1343             if let hir::ItemKind::Mod(..) = it.kind {}
1344             else {
1345                 self.items_nameable = false;
1346                 self.boundary = it.hir_id;
1347             }
1348             return;
1349         }
1350
1351         if let Some(attr) = attr::find_by_name(&it.attrs, sym::rustc_test_marker) {
1352             cx.struct_span_lint(
1353                 UNNAMEABLE_TEST_ITEMS,
1354                 attr.span,
1355                 "cannot test inner items",
1356             ).emit();
1357         }
1358     }
1359
1360     fn check_item_post(&mut self, _cx: &LateContext<'_, '_>, it: &hir::Item) {
1361         if !self.items_nameable && self.boundary == it.hir_id {
1362             self.items_nameable = true;
1363         }
1364     }
1365 }
1366
1367 declare_lint! {
1368     pub KEYWORD_IDENTS,
1369     Allow,
1370     "detects edition keywords being used as an identifier",
1371     @future_incompatible = FutureIncompatibleInfo {
1372         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1373         edition: Some(Edition::Edition2018),
1374     };
1375 }
1376
1377 declare_lint_pass!(
1378     /// Check for uses of edition keywords used as an identifier.
1379     KeywordIdents => [KEYWORD_IDENTS]
1380 );
1381
1382 struct UnderMacro(bool);
1383
1384 impl KeywordIdents {
1385     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1386         for tt in tokens.into_trees() {
1387             match tt {
1388                 // Only report non-raw idents.
1389                 TokenTree::Token(token) => if let Some((ident, false)) = token.ident() {
1390                     self.check_ident_token(cx, UnderMacro(true), ident);
1391                 }
1392                 TokenTree::Delimited(_, _, tts) => {
1393                     self.check_tokens(cx, tts)
1394                 },
1395             }
1396         }
1397     }
1398
1399     fn check_ident_token(&mut self,
1400                          cx: &EarlyContext<'_>,
1401                          UnderMacro(under_macro): UnderMacro,
1402                          ident: ast::Ident)
1403     {
1404         let next_edition = match cx.sess.edition() {
1405             Edition::Edition2015 => {
1406                 match ident.name {
1407                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1408
1409                     // rust-lang/rust#56327: Conservatively do not
1410                     // attempt to report occurrences of `dyn` within
1411                     // macro definitions or invocations, because `dyn`
1412                     // can legitimately occur as a contextual keyword
1413                     // in 2015 code denoting its 2018 meaning, and we
1414                     // do not want rustfix to inject bugs into working
1415                     // code by rewriting such occurrences.
1416                     //
1417                     // But if we see `dyn` outside of a macro, we know
1418                     // its precise role in the parsed AST and thus are
1419                     // assured this is truly an attempt to use it as
1420                     // an identifier.
1421                     kw::Dyn if !under_macro => Edition::Edition2018,
1422
1423                     _ => return,
1424                 }
1425             }
1426
1427             // There are no new keywords yet for the 2018 edition and beyond.
1428             _ => return,
1429         };
1430
1431         // Don't lint `r#foo`.
1432         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1433             return;
1434         }
1435
1436         let mut lint = cx.struct_span_lint(
1437             KEYWORD_IDENTS,
1438             ident.span,
1439             &format!("`{}` is a keyword in the {} edition", ident, next_edition),
1440         );
1441         lint.span_suggestion(
1442             ident.span,
1443             "you can use a raw identifier to stay compatible",
1444             format!("r#{}", ident),
1445             Applicability::MachineApplicable,
1446         );
1447         lint.emit()
1448     }
1449 }
1450
1451 impl EarlyLintPass for KeywordIdents {
1452     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
1453         self.check_tokens(cx, mac_def.body.inner_tokens());
1454     }
1455     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::Mac) {
1456         self.check_tokens(cx, mac.args.inner_tokens());
1457     }
1458     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: ast::Ident) {
1459         self.check_ident_token(cx, UnderMacro(false), ident);
1460     }
1461 }
1462
1463 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
1464
1465 impl ExplicitOutlivesRequirements {
1466     fn lifetimes_outliving_lifetime<'tcx>(
1467         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1468         index: u32,
1469     ) -> Vec<ty::Region<'tcx>> {
1470         inferred_outlives.iter().filter_map(|(pred, _)| {
1471             match pred {
1472                 ty::Predicate::RegionOutlives(outlives) => {
1473                     let outlives = outlives.skip_binder();
1474                     match outlives.0 {
1475                         ty::ReEarlyBound(ebr) if ebr.index == index => {
1476                             Some(outlives.1)
1477                         }
1478                         _ => None,
1479                     }
1480                 }
1481                 _ => None
1482             }
1483         }).collect()
1484     }
1485
1486     fn lifetimes_outliving_type<'tcx>(
1487         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1488         index: u32,
1489     ) -> Vec<ty::Region<'tcx>> {
1490         inferred_outlives.iter().filter_map(|(pred, _)| {
1491             match pred {
1492                 ty::Predicate::TypeOutlives(outlives) => {
1493                     let outlives = outlives.skip_binder();
1494                     outlives.0.is_param(index).then_some(outlives.1)
1495                 }
1496                 _ => None
1497             }
1498         }).collect()
1499     }
1500
1501     fn collect_outlived_lifetimes<'tcx>(
1502         &self,
1503         param: &'tcx hir::GenericParam,
1504         tcx: TyCtxt<'tcx>,
1505         inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
1506         ty_generics: &'tcx ty::Generics,
1507     ) -> Vec<ty::Region<'tcx>> {
1508         let index = ty_generics.param_def_id_to_index[
1509             &tcx.hir().local_def_id(param.hir_id)];
1510
1511         match param.kind {
1512             hir::GenericParamKind::Lifetime { .. } => {
1513                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
1514             }
1515             hir::GenericParamKind::Type { .. } => {
1516                 Self::lifetimes_outliving_type(inferred_outlives, index)
1517             }
1518             hir::GenericParamKind::Const { .. } => Vec::new(),
1519         }
1520     }
1521
1522
1523     fn collect_outlives_bound_spans<'tcx>(
1524         &self,
1525         tcx: TyCtxt<'tcx>,
1526         bounds: &hir::GenericBounds,
1527         inferred_outlives: &[ty::Region<'tcx>],
1528         infer_static: bool,
1529     ) -> Vec<(usize, Span)> {
1530         use rustc::middle::resolve_lifetime::Region;
1531
1532         bounds
1533             .iter()
1534             .enumerate()
1535             .filter_map(|(i, bound)| {
1536                 if let hir::GenericBound::Outlives(lifetime) = bound {
1537                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
1538                         Some(Region::Static) if infer_static => {
1539                             inferred_outlives.iter()
1540                                 .any(|r| if let ty::ReStatic = r { true } else { false })
1541                         }
1542                         Some(Region::EarlyBound(index, ..)) => inferred_outlives
1543                             .iter()
1544                             .any(|r| {
1545                                 if let ty::ReEarlyBound(ebr) = r {
1546                                     ebr.index == index
1547                                 } else {
1548                                     false
1549                                 }
1550                             }),
1551                         _ => false,
1552                     };
1553                     is_inferred.then_some((i, bound.span()))
1554                 } else {
1555                     None
1556                 }
1557             })
1558             .collect()
1559     }
1560
1561     fn consolidate_outlives_bound_spans(
1562         &self,
1563         lo: Span,
1564         bounds: &hir::GenericBounds,
1565         bound_spans: Vec<(usize, Span)>
1566     ) -> Vec<Span> {
1567         if bounds.is_empty() {
1568             return Vec::new();
1569         }
1570         if bound_spans.len() == bounds.len() {
1571             let (_, last_bound_span) = bound_spans[bound_spans.len()-1];
1572             // If all bounds are inferable, we want to delete the colon, so
1573             // start from just after the parameter (span passed as argument)
1574             vec![lo.to(last_bound_span)]
1575         } else {
1576             let mut merged = Vec::new();
1577             let mut last_merged_i = None;
1578
1579             let mut from_start = true;
1580             for (i, bound_span) in bound_spans {
1581                 match last_merged_i {
1582                     // If the first bound is inferable, our span should also eat the leading `+`.
1583                     None if i == 0 => {
1584                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
1585                         last_merged_i = Some(0);
1586                     },
1587                     // If consecutive bounds are inferable, merge their spans
1588                     Some(h) if i == h+1 => {
1589                         if let Some(tail) = merged.last_mut() {
1590                             // Also eat the trailing `+` if the first
1591                             // more-than-one bound is inferable
1592                             let to_span = if from_start && i < bounds.len() {
1593                                 bounds[i+1].span().shrink_to_lo()
1594                             } else {
1595                                 bound_span
1596                             };
1597                             *tail = tail.to(to_span);
1598                             last_merged_i = Some(i);
1599                         } else {
1600                             bug!("another bound-span visited earlier");
1601                         }
1602                     },
1603                     _ => {
1604                         // When we find a non-inferable bound, subsequent inferable bounds
1605                         // won't be consecutive from the start (and we'll eat the leading
1606                         // `+` rather than the trailing one)
1607                         from_start = false;
1608                         merged.push(bounds[i-1].span().shrink_to_hi().to(bound_span));
1609                         last_merged_i = Some(i);
1610                     }
1611                 }
1612             }
1613             merged
1614         }
1615     }
1616 }
1617
1618 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExplicitOutlivesRequirements {
1619     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
1620         use rustc::middle::resolve_lifetime::Region;
1621
1622         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
1623         let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1624         if let hir::ItemKind::Struct(_, ref hir_generics)
1625             | hir::ItemKind::Enum(_, ref hir_generics)
1626             | hir::ItemKind::Union(_, ref hir_generics) = item.kind
1627         {
1628             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
1629             if inferred_outlives.is_empty() {
1630                 return;
1631             }
1632
1633             let ty_generics = cx.tcx.generics_of(def_id);
1634
1635             let mut bound_count = 0;
1636             let mut lint_spans = Vec::new();
1637
1638             for param in &hir_generics.params {
1639                 let has_lifetime_bounds = param.bounds.iter().any(|bound| {
1640                     if let hir::GenericBound::Outlives(_) = bound {
1641                         true
1642                     } else {
1643                         false
1644                     }
1645                 });
1646                 if !has_lifetime_bounds {
1647                     continue;
1648                 }
1649
1650                 let relevant_lifetimes = self.collect_outlived_lifetimes(
1651                     param,
1652                     cx.tcx,
1653                     inferred_outlives,
1654                     ty_generics,
1655                 );
1656                 if relevant_lifetimes.is_empty() {
1657                     continue;
1658                 }
1659
1660                 let bound_spans = self.collect_outlives_bound_spans(
1661                     cx.tcx, &param.bounds, &relevant_lifetimes, infer_static,
1662                 );
1663                 bound_count += bound_spans.len();
1664                 lint_spans.extend(
1665                     self.consolidate_outlives_bound_spans(
1666                         param.span.shrink_to_hi(), &param.bounds, bound_spans
1667                     )
1668                 );
1669             }
1670
1671             let mut where_lint_spans = Vec::new();
1672             let mut dropped_predicate_count = 0;
1673             let num_predicates = hir_generics.where_clause.predicates.len();
1674             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
1675                 let (relevant_lifetimes, bounds, span) = match where_predicate {
1676                     hir::WherePredicate::RegionPredicate(predicate) => {
1677                         if let Some(Region::EarlyBound(index, ..))
1678                             = cx.tcx.named_region(predicate.lifetime.hir_id)
1679                         {
1680                             (
1681                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
1682                                 &predicate.bounds,
1683                                 predicate.span,
1684                             )
1685                         } else {
1686                             continue;
1687                         }
1688                     }
1689                     hir::WherePredicate::BoundPredicate(predicate) => {
1690                         // FIXME we can also infer bounds on associated types,
1691                         // and should check for them here.
1692                         match predicate.bounded_ty.kind {
1693                             hir::TyKind::Path(hir::QPath::Resolved(
1694                                 None,
1695                                 ref path,
1696                             )) => {
1697                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
1698                                     let index = ty_generics.param_def_id_to_index[&def_id];
1699                                     (
1700                                         Self::lifetimes_outliving_type(inferred_outlives, index),
1701                                         &predicate.bounds,
1702                                         predicate.span,
1703                                     )
1704                                 } else {
1705                                     continue;
1706                                 }
1707                             },
1708                             _ => { continue; }
1709                         }
1710                     }
1711                     _ => continue,
1712                 };
1713                 if relevant_lifetimes.is_empty() {
1714                     continue;
1715                 }
1716
1717                 let bound_spans = self.collect_outlives_bound_spans(
1718                     cx.tcx, bounds, &relevant_lifetimes, infer_static,
1719                 );
1720                 bound_count += bound_spans.len();
1721
1722                 let drop_predicate = bound_spans.len() == bounds.len();
1723                 if drop_predicate {
1724                     dropped_predicate_count += 1;
1725                 }
1726
1727                 // If all the bounds on a predicate were inferable and there are
1728                 // further predicates, we want to eat the trailing comma.
1729                 if drop_predicate && i + 1 < num_predicates {
1730                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
1731                     where_lint_spans.push(
1732                         span.to(next_predicate_span.shrink_to_lo())
1733                     );
1734                 } else {
1735                     where_lint_spans.extend(
1736                         self.consolidate_outlives_bound_spans(
1737                             span.shrink_to_lo(),
1738                             bounds,
1739                             bound_spans
1740                         )
1741                     );
1742                 }
1743             }
1744
1745             // If all predicates are inferable, drop the entire clause
1746             // (including the `where`)
1747             if num_predicates > 0 && dropped_predicate_count == num_predicates {
1748                 let where_span = hir_generics.where_clause.span()
1749                     .expect("span of (nonempty) where clause should exist");
1750                 // Extend the where clause back to the closing `>` of the
1751                 // generics, except for tuple struct, which have the `where`
1752                 // after the fields of the struct.
1753                 let full_where_span = if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _)
1754                         = item.kind
1755                 {
1756                     where_span
1757                 } else {
1758                     hir_generics.span.shrink_to_hi().to(where_span)
1759                 };
1760                 lint_spans.push(
1761                     full_where_span
1762                 );
1763             } else {
1764                 lint_spans.extend(where_lint_spans);
1765             }
1766
1767             if !lint_spans.is_empty() {
1768                 let mut err = cx.struct_span_lint(
1769                     EXPLICIT_OUTLIVES_REQUIREMENTS,
1770                     lint_spans.clone(),
1771                     "outlives requirements can be inferred"
1772                 );
1773                 err.multipart_suggestion(
1774                     if bound_count == 1 {
1775                         "remove this bound"
1776                     } else {
1777                         "remove these bounds"
1778                     },
1779                     lint_spans.into_iter().map(|span| (span, "".to_owned())).collect::<Vec<_>>(),
1780                     Applicability::MachineApplicable
1781                 );
1782                 err.emit();
1783             }
1784         }
1785     }
1786 }
1787
1788 declare_lint! {
1789     pub INCOMPLETE_FEATURES,
1790     Warn,
1791     "incomplete features that may function improperly in some or all cases"
1792 }
1793
1794 declare_lint_pass!(
1795     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `feature_gate.rs`.
1796     IncompleteFeatures => [INCOMPLETE_FEATURES]
1797 );
1798
1799 impl EarlyLintPass for IncompleteFeatures {
1800     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
1801         let features = cx.sess.features_untracked();
1802         features.declared_lang_features
1803             .iter().map(|(name, span, _)| (name, span))
1804             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
1805             .filter(|(name, _)| rustc_feature::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
1806             .for_each(|(name, &span)| {
1807                 cx.struct_span_lint(
1808                     INCOMPLETE_FEATURES,
1809                     span,
1810                     &format!(
1811                         "the feature `{}` is incomplete and may cause the compiler to crash",
1812                         name,
1813                     )
1814                 )
1815                 .emit();
1816             });
1817     }
1818 }
1819
1820 declare_lint! {
1821     pub INVALID_VALUE,
1822     Warn,
1823     "an invalid value is being created (such as a NULL reference)"
1824 }
1825
1826 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
1827
1828 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidValue {
1829     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &hir::Expr) {
1830
1831         #[derive(Debug, Copy, Clone, PartialEq)]
1832         enum InitKind { Zeroed, Uninit };
1833
1834         /// Information about why a type cannot be initialized this way.
1835         /// Contains an error message and optionally a span to point at.
1836         type InitError = (String, Option<Span>);
1837
1838         /// Test if this constant is all-0.
1839         fn is_zero(expr: &hir::Expr) -> bool {
1840             use hir::ExprKind::*;
1841             use syntax::ast::LitKind::*;
1842             match &expr.kind {
1843                 Lit(lit) =>
1844                     if let Int(i, _) = lit.node {
1845                         i == 0
1846                     } else {
1847                         false
1848                     },
1849                 Tup(tup) =>
1850                     tup.iter().all(is_zero),
1851                 _ =>
1852                     false
1853             }
1854         }
1855
1856         /// Determine if this expression is a "dangerous initialization".
1857         fn is_dangerous_init(cx: &LateContext<'_, '_>, expr: &hir::Expr) -> Option<InitKind> {
1858             // `transmute` is inside an anonymous module (the `extern` block?);
1859             // `Invalid` represents the empty string and matches that.
1860             // FIXME(#66075): use diagnostic items.  Somehow, that does not seem to work
1861             // on intrinsics right now.
1862             const TRANSMUTE_PATH: &[Symbol] =
1863                 &[sym::core, sym::intrinsics, kw::Invalid, sym::transmute];
1864
1865             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
1866                 // Find calls to `mem::{uninitialized,zeroed}` methods.
1867                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1868                     let def_id = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1869
1870                     if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
1871                         return Some(InitKind::Zeroed);
1872                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
1873                         return Some(InitKind::Uninit);
1874                     } else if cx.match_def_path(def_id, TRANSMUTE_PATH) {
1875                         if is_zero(&args[0]) {
1876                             return Some(InitKind::Zeroed);
1877                         }
1878                     }
1879                 }
1880             } else if let hir::ExprKind::MethodCall(_, _, ref args) = expr.kind {
1881                 // Find problematic calls to `MaybeUninit::assume_init`.
1882                 let def_id = cx.tables.type_dependent_def_id(expr.hir_id)?;
1883                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
1884                     // This is a call to *some* method named `assume_init`.
1885                     // See if the `self` parameter is one of the dangerous constructors.
1886                     if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
1887                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1888                             let def_id = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1889
1890                             if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
1891                                 return Some(InitKind::Zeroed);
1892                             } else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
1893                                 return Some(InitKind::Uninit);
1894                             }
1895                         }
1896                     }
1897                 }
1898             }
1899
1900             None
1901         }
1902
1903         /// Return `Some` only if we are sure this type does *not*
1904         /// allow zero initialization.
1905         fn ty_find_init_error<'tcx>(
1906             tcx: TyCtxt<'tcx>,
1907             ty: Ty<'tcx>,
1908             init: InitKind,
1909         ) -> Option<InitError> {
1910             use rustc::ty::TyKind::*;
1911             match ty.kind {
1912                 // Primitive types that don't like 0 as a value.
1913                 Ref(..) => Some((format!("References must be non-null"), None)),
1914                 Adt(..) if ty.is_box() => Some((format!("`Box` must be non-null"), None)),
1915                 FnPtr(..) => Some((format!("Function pointers must be non-null"), None)),
1916                 Never => Some((format!("The never type (`!`) has no valid value"), None)),
1917                 RawPtr(tm) if matches!(tm.ty.kind, Dynamic(..)) => // raw ptr to dyn Trait
1918                     Some((format!("The vtable of a wide raw pointer must be non-null"), None)),
1919                 // Primitive types with other constraints.
1920                 Bool if init == InitKind::Uninit =>
1921                     Some((format!("Booleans must be `true` or `false`"), None)),
1922                 Char if init == InitKind::Uninit =>
1923                     Some((format!("Characters must be a valid unicode codepoint"), None)),
1924                 // Recurse and checks for some compound types.
1925                 Adt(adt_def, substs) if !adt_def.is_union() => {
1926                     // First check f this ADT has a layout attribute (like `NonNull` and friends).
1927                     use std::ops::Bound;
1928                     match tcx.layout_scalar_valid_range(adt_def.did) {
1929                         // We exploit here that `layout_scalar_valid_range` will never
1930                         // return `Bound::Excluded`.  (And we have tests checking that we
1931                         // handle the attribute correctly.)
1932                         (Bound::Included(lo), _) if lo > 0 =>
1933                             return Some((format!("{} must be non-null", ty), None)),
1934                         (Bound::Included(_), _) | (_, Bound::Included(_))
1935                         if init == InitKind::Uninit =>
1936                             return Some((
1937                                 format!("{} must be initialized inside its custom valid range", ty),
1938                                 None,
1939                             )),
1940                         _ => {}
1941                     }
1942                     // Now, recurse.
1943                     match adt_def.variants.len() {
1944                         0 => Some((format!("0-variant enums have no valid value"), None)),
1945                         1 => {
1946                             // Struct, or enum with exactly one variant.
1947                             // Proceed recursively, check all fields.
1948                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
1949                             variant.fields.iter().find_map(|field| {
1950                                 ty_find_init_error(
1951                                     tcx,
1952                                     field.ty(tcx, substs),
1953                                     init,
1954                                 ).map(|(mut msg, span)| if span.is_none() {
1955                                     // Point to this field, should be helpful for figuring
1956                                     // out where the source of the error is.
1957                                     let span = tcx.def_span(field.did);
1958                                     write!(&mut msg, " (in this {} field)", adt_def.descr())
1959                                         .unwrap();
1960                                     (msg, Some(span))
1961                                 } else {
1962                                     // Just forward.
1963                                     (msg, span)
1964                                 })
1965                             })
1966                         }
1967                         // Multi-variant enums are tricky: if all but one variant are
1968                         // uninhabited, we might actually do layout like for a single-variant
1969                         // enum, and then even leaving them uninitialized could be okay.
1970                         _ => None, // Conservative fallback for multi-variant enum.
1971                     }
1972                 }
1973                 Tuple(..) => {
1974                     // Proceed recursively, check all fields.
1975                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
1976                 }
1977                 // Conservative fallback.
1978                 _ => None,
1979             }
1980         }
1981
1982         if let Some(init) = is_dangerous_init(cx, expr) {
1983             // This conjures an instance of a type out of nothing,
1984             // using zeroed or uninitialized memory.
1985             // We are extremely conservative with what we warn about.
1986             let conjured_ty = cx.tables.expr_ty(expr);
1987             if let Some((msg, span)) = ty_find_init_error(cx.tcx, conjured_ty, init) {
1988                 let mut err = cx.struct_span_lint(
1989                     INVALID_VALUE,
1990                     expr.span,
1991                     &format!(
1992                         "the type `{}` does not permit {}",
1993                         conjured_ty,
1994                         match init {
1995                             InitKind::Zeroed => "zero-initialization",
1996                             InitKind::Uninit => "being left uninitialized",
1997                         },
1998                     ),
1999                 );
2000                 err.span_label(expr.span,
2001                     "this code causes undefined behavior when executed");
2002                 err.span_label(expr.span, "help: use `MaybeUninit<T>` instead, \
2003                     and only call `assume_init` after initialization is done");
2004                 if let Some(span) = span {
2005                     err.span_note(span, &msg);
2006                 } else {
2007                     err.note(&msg);
2008                 }
2009                 err.emit();
2010             }
2011         }
2012     }
2013 }