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, LOCAL_CRATE};
  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
  38 use syntax::tokenstream::{TokenTree, TokenStream};
  39 use syntax::ast::{self, Expr};
  40 use syntax::ptr::P;
  41 use syntax::attr::{self, HasAttrs, AttributeTemplate};
  42 use syntax::source_map::Spanned;
  43 use syntax::edition::Edition;
  44 use syntax::feature_gate::{self, AttributeGate, AttributeType};
  45 use syntax::feature_gate::{Stability, deprecated_attributes};
  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.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_sugared_doc {
 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_sugared_doc).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     PLUGIN_AS_LIBRARY,
 805     Warn,
 806     "compiler plugin used as ordinary library in non-plugin crate"
 807 }
 808
 809 declare_lint_pass!(PluginAsLibrary => [PLUGIN_AS_LIBRARY]);
 810
 811 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PluginAsLibrary {
 812     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
 813         if cx.tcx.plugin_registrar_fn(LOCAL_CRATE).is_some() {
 814             // We're compiling a plugin; it's fine to link other plugins.
 815             return;
 816         }
 817
 818         match it.kind {
 819             hir::ItemKind::ExternCrate(..) => (),
 820             _ => return,
 821         };
 822
 823         let def_id = cx.tcx.hir().local_def_id(it.hir_id);
 824         let prfn = match cx.tcx.extern_mod_stmt_cnum(def_id) {
 825             Some(cnum) => cx.tcx.plugin_registrar_fn(cnum),
 826             None => {
 827                 // Probably means we aren't linking the crate for some reason.
 828                 //
 829                 // Not sure if / when this could happen.
 830                 return;
 831             }
 832         };
 833
 834         if prfn.is_some() {
 835             cx.span_lint(PLUGIN_AS_LIBRARY,
 836                          it.span,
 837                          "compiler plugin used as an ordinary library");
 838         }
 839     }
 840 }
 841
 842 declare_lint! {
 843     NO_MANGLE_CONST_ITEMS,
 844     Deny,
 845     "const items will not have their symbols exported"
 846 }
 847
 848 declare_lint! {
 849     NO_MANGLE_GENERIC_ITEMS,
 850     Warn,
 851     "generic items must be mangled"
 852 }
 853
 854 declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
 855
 856 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidNoMangleItems {
 857     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
 858         match it.kind {
 859             hir::ItemKind::Fn(.., ref generics, _) => {
 860                 if let Some(no_mangle_attr) = attr::find_by_name(&it.attrs, sym::no_mangle) {
 861                     for param in &generics.params {
 862                         match param.kind {
 863                             GenericParamKind::Lifetime { .. } => {}
 864                             GenericParamKind::Type { .. } |
 865                             GenericParamKind::Const { .. } => {
 866                                 let mut err = cx.struct_span_lint(
 867                                     NO_MANGLE_GENERIC_ITEMS,
 868                                     it.span,
 869                                     "functions generic over types or consts must be mangled",
 870                                 );
 871                                 err.span_suggestion_short(
 872                                     no_mangle_attr.span,
 873                                     "remove this attribute",
 874                                     String::new(),
 875                                     // Use of `#[no_mangle]` suggests FFI intent; correct
 876                                     // fix may be to monomorphize source by hand
 877                                     Applicability::MaybeIncorrect
 878                                 );
 879                                 err.emit();
 880                                 break;
 881                             }
 882                         }
 883                     }
 884                 }
 885             }
 886             hir::ItemKind::Const(..) => {
 887                 if attr::contains_name(&it.attrs, sym::no_mangle) {
 888                     // Const items do not refer to a particular location in memory, and therefore
 889                     // don't have anything to attach a symbol to
 890                     let msg = "const items should never be `#[no_mangle]`";
 891                     let mut err = cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, msg);
 892
 893                     // account for "pub const" (#45562)
 894                     let start = cx.tcx.sess.source_map().span_to_snippet(it.span)
 895                         .map(|snippet| snippet.find("const").unwrap_or(0))
 896                         .unwrap_or(0) as u32;
 897                     // `const` is 5 chars
 898                     let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
 899                     err.span_suggestion(
 900                         const_span,
 901                         "try a static value",
 902                         "pub static".to_owned(),
 903                         Applicability::MachineApplicable
 904                     );
 905                     err.emit();
 906                 }
 907             }
 908             _ => {}
 909         }
 910     }
 911 }
 912
 913 declare_lint! {
 914     MUTABLE_TRANSMUTES,
 915     Deny,
 916     "mutating transmuted &mut T from &T may cause undefined behavior"
 917 }
 918
 919 declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
 920
 921 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutableTransmutes {
 922     fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &hir::Expr) {
 923         use rustc_target::spec::abi::Abi::RustIntrinsic;
 924
 925         let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
 926                    consider instead using an UnsafeCell";
 927         match get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (&ty1.kind, &ty2.kind)) {
 928             Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) => {
 929                 if to_mt == hir::Mutability::MutMutable &&
 930                    from_mt == hir::Mutability::MutImmutable {
 931                     cx.span_lint(MUTABLE_TRANSMUTES, expr.span, msg);
 932                 }
 933             }
 934             _ => (),
 935         }
 936
 937         fn get_transmute_from_to<'a, 'tcx>
 938             (cx: &LateContext<'a, 'tcx>,
 939              expr: &hir::Expr)
 940              -> Option<(Ty<'tcx>, Ty<'tcx>)> {
 941             let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
 942                 cx.tables.qpath_res(qpath, expr.hir_id)
 943             } else {
 944                 return None;
 945             };
 946             if let Res::Def(DefKind::Fn, did) = def {
 947                 if !def_id_is_transmute(cx, did) {
 948                     return None;
 949                 }
 950                 let sig = cx.tables.node_type(expr.hir_id).fn_sig(cx.tcx);
 951                 let from = sig.inputs().skip_binder()[0];
 952                 let to = *sig.output().skip_binder();
 953                 return Some((from, to));
 954             }
 955             None
 956         }
 957
 958         fn def_id_is_transmute(cx: &LateContext<'_, '_>, def_id: DefId) -> bool {
 959             cx.tcx.fn_sig(def_id).abi() == RustIntrinsic &&
 960             cx.tcx.item_name(def_id) == sym::transmute
 961         }
 962     }
 963 }
 964
 965 declare_lint! {
 966     UNSTABLE_FEATURES,
 967     Allow,
 968     "enabling unstable features (deprecated. do not use)"
 969 }
 970
 971 declare_lint_pass!(
 972     /// Forbids using the `#[feature(...)]` attribute
 973     UnstableFeatures => [UNSTABLE_FEATURES]
 974 );
 975
 976 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnstableFeatures {
 977     fn check_attribute(&mut self, ctx: &LateContext<'_, '_>, attr: &ast::Attribute) {
 978         if attr.check_name(sym::feature) {
 979             if let Some(items) = attr.meta_item_list() {
 980                 for item in items {
 981                     ctx.span_lint(UNSTABLE_FEATURES, item.span(), "unstable feature");
 982                 }
 983             }
 984         }
 985     }
 986 }
 987
 988 declare_lint! {
 989     pub UNREACHABLE_PUB,
 990     Allow,
 991     "`pub` items not reachable from crate root"
 992 }
 993
 994 declare_lint_pass!(
 995     /// Lint for items marked `pub` that aren't reachable from other crates.
 996     UnreachablePub => [UNREACHABLE_PUB]
 997 );
 998
 999 impl UnreachablePub {
1000     fn perform_lint(&self, cx: &LateContext<'_, '_>, what: &str, id: hir::HirId,
1001                     vis: &hir::Visibility, span: Span, exportable: bool) {
1002         let mut applicability = Applicability::MachineApplicable;
1003         match vis.node {
1004             hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
1005                 if span.from_expansion() {
1006                     applicability = Applicability::MaybeIncorrect;
1007                 }
1008                 let def_span = cx.tcx.sess.source_map().def_span(span);
1009                 let mut err = cx.struct_span_lint(UNREACHABLE_PUB, def_span,
1010                                                   &format!("unreachable `pub` {}", what));
1011                 let replacement = if cx.tcx.features().crate_visibility_modifier {
1012                     "crate"
1013                 } else {
1014                     "pub(crate)"
1015                 }.to_owned();
1016
1017                 err.span_suggestion(
1018                     vis.span,
1019                     "consider restricting its visibility",
1020                     replacement,
1021                     applicability,
1022                 );
1023                 if exportable {
1024                     err.help("or consider exporting it for use by other crates");
1025                 }
1026                 err.emit();
1027             },
1028             _ => {}
1029         }
1030     }
1031 }
1032
1033 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnreachablePub {
1034     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
1035         self.perform_lint(cx, "item", item.hir_id, &item.vis, item.span, true);
1036     }
1037
1038     fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, foreign_item: &hir::ForeignItem) {
1039         self.perform_lint(cx, "item", foreign_item.hir_id, &foreign_item.vis,
1040                           foreign_item.span, true);
1041     }
1042
1043     fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, field: &hir::StructField) {
1044         self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
1045     }
1046
1047     fn check_impl_item(&mut self, cx: &LateContext<'_, '_>, impl_item: &hir::ImplItem) {
1048         self.perform_lint(cx, "item", impl_item.hir_id, &impl_item.vis, impl_item.span, false);
1049     }
1050 }
1051
1052 declare_lint! {
1053     TYPE_ALIAS_BOUNDS,
1054     Warn,
1055     "bounds in type aliases are not enforced"
1056 }
1057
1058 declare_lint_pass!(
1059     /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
1060     /// They are relevant when using associated types, but otherwise neither checked
1061     /// at definition site nor enforced at use site.
1062     TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
1063 );
1064
1065 impl TypeAliasBounds {
1066     fn is_type_variable_assoc(qpath: &hir::QPath) -> bool {
1067         match *qpath {
1068             hir::QPath::TypeRelative(ref ty, _) => {
1069                 // If this is a type variable, we found a `T::Assoc`.
1070                 match ty.kind {
1071                     hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1072                         match path.res {
1073                             Res::Def(DefKind::TyParam, _) => true,
1074                             _ => false
1075                         }
1076                     }
1077                     _ => false
1078                 }
1079             }
1080             hir::QPath::Resolved(..) => false,
1081         }
1082     }
1083
1084     fn suggest_changing_assoc_types(ty: &hir::Ty, err: &mut DiagnosticBuilder<'_>) {
1085         // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
1086         // bound.  Let's see if this type does that.
1087
1088         // We use a HIR visitor to walk the type.
1089         use rustc::hir::intravisit::{self, Visitor};
1090         struct WalkAssocTypes<'a, 'db> {
1091             err: &'a mut DiagnosticBuilder<'db>
1092         }
1093         impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
1094             fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'v>
1095             {
1096                 intravisit::NestedVisitorMap::None
1097             }
1098
1099             fn visit_qpath(&mut self, qpath: &'v hir::QPath, id: hir::HirId, span: Span) {
1100                 if TypeAliasBounds::is_type_variable_assoc(qpath) {
1101                     self.err.span_help(span,
1102                         "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
1103                          associated types in type aliases");
1104                 }
1105                 intravisit::walk_qpath(self, qpath, id, span)
1106             }
1107         }
1108
1109         // Let's go for a walk!
1110         let mut visitor = WalkAssocTypes { err };
1111         visitor.visit_ty(ty);
1112     }
1113 }
1114
1115 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeAliasBounds {
1116     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
1117         let (ty, type_alias_generics) = match item.kind {
1118             hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
1119             _ => return,
1120         };
1121         let mut suggested_changing_assoc_types = false;
1122         // There must not be a where clause
1123         if !type_alias_generics.where_clause.predicates.is_empty() {
1124             let spans : Vec<_> = type_alias_generics.where_clause.predicates.iter()
1125                 .map(|pred| pred.span()).collect();
1126             let mut err = cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans,
1127                 "where clauses are not enforced in type aliases");
1128             err.help("the clause will not be checked when the type alias is used, \
1129                       and should be removed");
1130             if !suggested_changing_assoc_types {
1131                 TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1132                 suggested_changing_assoc_types = true;
1133             }
1134             err.emit();
1135         }
1136         // The parameters must not have bounds
1137         for param in type_alias_generics.params.iter() {
1138             let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
1139             if !spans.is_empty() {
1140                 let mut err = cx.struct_span_lint(
1141                     TYPE_ALIAS_BOUNDS,
1142                     spans,
1143                     "bounds on generic parameters are not enforced in type aliases",
1144                 );
1145                 err.help("the bound will not be checked when the type alias is used, \
1146                           and should be removed");
1147                 if !suggested_changing_assoc_types {
1148                     TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
1149                     suggested_changing_assoc_types = true;
1150                 }
1151                 err.emit();
1152             }
1153         }
1154     }
1155 }
1156
1157 declare_lint_pass!(
1158     /// Lint constants that are erroneous.
1159     /// Without this lint, we might not get any diagnostic if the constant is
1160     /// unused within this crate, even though downstream crates can't use it
1161     /// without producing an error.
1162     UnusedBrokenConst => []
1163 );
1164
1165 fn check_const(cx: &LateContext<'_, '_>, body_id: hir::BodyId) {
1166     let def_id = cx.tcx.hir().body_owner_def_id(body_id);
1167     let param_env = if cx.tcx.is_static(def_id) {
1168         // Use the same param_env as `codegen_static_initializer`, to reuse the cache.
1169         ty::ParamEnv::reveal_all()
1170     } else {
1171         cx.tcx.param_env(def_id)
1172     };
1173     let cid = ::rustc::mir::interpret::GlobalId {
1174         instance: ty::Instance::mono(cx.tcx, def_id),
1175         promoted: None
1176     };
1177     // trigger the query once for all constants since that will already report the errors
1178     // FIXME: Use ensure here
1179     let _ = cx.tcx.const_eval(param_env.and(cid));
1180 }
1181
1182 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedBrokenConst {
1183     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
1184         match it.kind {
1185             hir::ItemKind::Const(_, body_id) => {
1186                 check_const(cx, body_id);
1187             },
1188             hir::ItemKind::Static(_, _, body_id) => {
1189                 check_const(cx, body_id);
1190             },
1191             _ => {},
1192         }
1193     }
1194 }
1195
1196 declare_lint! {
1197     TRIVIAL_BOUNDS,
1198     Warn,
1199     "these bounds don't depend on an type parameters"
1200 }
1201
1202 declare_lint_pass!(
1203     /// Lint for trait and lifetime bounds that don't depend on type parameters
1204     /// which either do nothing, or stop the item from being used.
1205     TrivialConstraints => [TRIVIAL_BOUNDS]
1206 );
1207
1208 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TrivialConstraints {
1209     fn check_item(
1210         &mut self,
1211         cx: &LateContext<'a, 'tcx>,
1212         item: &'tcx hir::Item,
1213     ) {
1214         use rustc::ty::fold::TypeFoldable;
1215         use rustc::ty::Predicate::*;
1216
1217         if cx.tcx.features().trivial_bounds {
1218             let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1219             let predicates = cx.tcx.predicates_of(def_id);
1220             for &(predicate, span) in predicates.predicates {
1221                 let predicate_kind_name = match predicate {
1222                     Trait(..) => "Trait",
1223                     TypeOutlives(..) |
1224                     RegionOutlives(..) => "Lifetime",
1225
1226                     // Ignore projections, as they can only be global
1227                     // if the trait bound is global
1228                     Projection(..) |
1229                     // Ignore bounds that a user can't type
1230                     WellFormed(..) |
1231                     ObjectSafe(..) |
1232                     ClosureKind(..) |
1233                     Subtype(..) |
1234                     ConstEvaluatable(..) => continue,
1235                 };
1236                 if predicate.is_global() {
1237                     cx.span_lint(
1238                         TRIVIAL_BOUNDS,
1239                         span,
1240                         &format!("{} bound {} does not depend on any type \
1241                                 or lifetime parameters", predicate_kind_name, predicate),
1242                     );
1243                 }
1244             }
1245         }
1246     }
1247 }
1248
1249 declare_lint_pass!(
1250     /// Does nothing as a lint pass, but registers some `Lint`s
1251     /// which are used by other parts of the compiler.
1252     SoftLints => [
1253         WHILE_TRUE,
1254         BOX_POINTERS,
1255         NON_SHORTHAND_FIELD_PATTERNS,
1256         UNSAFE_CODE,
1257         MISSING_DOCS,
1258         MISSING_COPY_IMPLEMENTATIONS,
1259         MISSING_DEBUG_IMPLEMENTATIONS,
1260         ANONYMOUS_PARAMETERS,
1261         UNUSED_DOC_COMMENTS,
1262         PLUGIN_AS_LIBRARY,
1263         NO_MANGLE_CONST_ITEMS,
1264         NO_MANGLE_GENERIC_ITEMS,
1265         MUTABLE_TRANSMUTES,
1266         UNSTABLE_FEATURES,
1267         UNREACHABLE_PUB,
1268         TYPE_ALIAS_BOUNDS,
1269         TRIVIAL_BOUNDS
1270     ]
1271 );
1272
1273 declare_lint! {
1274     pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
1275     Warn,
1276     "`...` range patterns are deprecated"
1277 }
1278
1279 #[derive(Default)]
1280 pub struct EllipsisInclusiveRangePatterns {
1281     /// If `Some(_)`, suppress all subsequent pattern
1282     /// warnings for better diagnostics.
1283     node_id: Option<ast::NodeId>,
1284 }
1285
1286 impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
1287
1288 impl EarlyLintPass for EllipsisInclusiveRangePatterns {
1289     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
1290         if self.node_id.is_some() {
1291             // Don't recursively warn about patterns inside range endpoints.
1292             return
1293         }
1294
1295         use self::ast::{PatKind, RangeEnd, RangeSyntax::DotDotDot};
1296
1297         /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
1298         /// corresponding to the ellipsis.
1299         fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(&P<Expr>, &P<Expr>, Span)> {
1300             match &pat.kind {
1301                 PatKind::Range(a, b, Spanned { span, node: RangeEnd::Included(DotDotDot), .. }) => {
1302                     Some((a, b, *span))
1303                 }
1304                 _ => None,
1305             }
1306         }
1307
1308         let (parenthesise, endpoints) = match &pat.kind {
1309             PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
1310             _ => (false, matches_ellipsis_pat(pat)),
1311         };
1312
1313         if let Some((start, end, join)) = endpoints {
1314             let msg = "`...` range patterns are deprecated";
1315             let suggestion = "use `..=` for an inclusive range";
1316             if parenthesise {
1317                 self.node_id = Some(pat.id);
1318                 let mut err = cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, msg);
1319                 err.span_suggestion(
1320                     pat.span,
1321                     suggestion,
1322                     format!("&({}..={})", expr_to_string(&start), expr_to_string(&end)),
1323                     Applicability::MachineApplicable,
1324                 );
1325                 err.emit();
1326             } else {
1327                 let mut err = cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, msg);
1328                 err.span_suggestion_short(
1329                     join,
1330                     suggestion,
1331                     "..=".to_owned(),
1332                     Applicability::MachineApplicable,
1333                 );
1334                 err.emit();
1335             };
1336         }
1337     }
1338
1339     fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
1340         if let Some(node_id) = self.node_id {
1341             if pat.id == node_id {
1342                 self.node_id = None
1343             }
1344         }
1345     }
1346 }
1347
1348 declare_lint! {
1349     UNNAMEABLE_TEST_ITEMS,
1350     Warn,
1351     "detects an item that cannot be named being marked as `#[test_case]`",
1352     report_in_external_macro
1353 }
1354
1355 pub struct UnnameableTestItems {
1356     boundary: hir::HirId, // HirId of the item under which things are not nameable
1357     items_nameable: bool,
1358 }
1359
1360 impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
1361
1362 impl UnnameableTestItems {
1363     pub fn new() -> Self {
1364         Self {
1365             boundary: hir::DUMMY_HIR_ID,
1366             items_nameable: true
1367         }
1368     }
1369 }
1370
1371 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnameableTestItems {
1372     fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
1373         if self.items_nameable {
1374             if let hir::ItemKind::Mod(..) = it.kind {}
1375             else {
1376                 self.items_nameable = false;
1377                 self.boundary = it.hir_id;
1378             }
1379             return;
1380         }
1381
1382         if let Some(attr) = attr::find_by_name(&it.attrs, sym::rustc_test_marker) {
1383             cx.struct_span_lint(
1384                 UNNAMEABLE_TEST_ITEMS,
1385                 attr.span,
1386                 "cannot test inner items",
1387             ).emit();
1388         }
1389     }
1390
1391     fn check_item_post(&mut self, _cx: &LateContext<'_, '_>, it: &hir::Item) {
1392         if !self.items_nameable && self.boundary == it.hir_id {
1393             self.items_nameable = true;
1394         }
1395     }
1396 }
1397
1398 declare_lint! {
1399     pub KEYWORD_IDENTS,
1400     Allow,
1401     "detects edition keywords being used as an identifier",
1402     @future_incompatible = FutureIncompatibleInfo {
1403         reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
1404         edition: Some(Edition::Edition2018),
1405     };
1406 }
1407
1408 declare_lint_pass!(
1409     /// Check for uses of edition keywords used as an identifier.
1410     KeywordIdents => [KEYWORD_IDENTS]
1411 );
1412
1413 struct UnderMacro(bool);
1414
1415 impl KeywordIdents {
1416     fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
1417         for tt in tokens.into_trees() {
1418             match tt {
1419                 // Only report non-raw idents.
1420                 TokenTree::Token(token) => if let Some((ident, false)) = token.ident() {
1421                     self.check_ident_token(cx, UnderMacro(true), ident);
1422                 }
1423                 TokenTree::Delimited(_, _, tts) => {
1424                     self.check_tokens(cx, tts)
1425                 },
1426             }
1427         }
1428     }
1429
1430     fn check_ident_token(&mut self,
1431                          cx: &EarlyContext<'_>,
1432                          UnderMacro(under_macro): UnderMacro,
1433                          ident: ast::Ident)
1434     {
1435         let next_edition = match cx.sess.edition() {
1436             Edition::Edition2015 => {
1437                 match ident.name {
1438                     kw::Async | kw::Await | kw::Try => Edition::Edition2018,
1439
1440                     // rust-lang/rust#56327: Conservatively do not
1441                     // attempt to report occurrences of `dyn` within
1442                     // macro definitions or invocations, because `dyn`
1443                     // can legitimately occur as a contextual keyword
1444                     // in 2015 code denoting its 2018 meaning, and we
1445                     // do not want rustfix to inject bugs into working
1446                     // code by rewriting such occurrences.
1447                     //
1448                     // But if we see `dyn` outside of a macro, we know
1449                     // its precise role in the parsed AST and thus are
1450                     // assured this is truly an attempt to use it as
1451                     // an identifier.
1452                     kw::Dyn if !under_macro => Edition::Edition2018,
1453
1454                     _ => return,
1455                 }
1456             }
1457
1458             // There are no new keywords yet for the 2018 edition and beyond.
1459             _ => return,
1460         };
1461
1462         // Don't lint `r#foo`.
1463         if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
1464             return;
1465         }
1466
1467         let mut lint = cx.struct_span_lint(
1468             KEYWORD_IDENTS,
1469             ident.span,
1470             &format!("`{}` is a keyword in the {} edition",
1471                      ident.as_str(),
1472                      next_edition),
1473         );
1474         lint.span_suggestion(
1475             ident.span,
1476             "you can use a raw identifier to stay compatible",
1477             format!("r#{}", ident.as_str()),
1478             Applicability::MachineApplicable,
1479         );
1480         lint.emit()
1481     }
1482 }
1483
1484 impl EarlyLintPass for KeywordIdents {
1485     fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
1486         self.check_tokens(cx, mac_def.stream());
1487     }
1488     fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::Mac) {
1489         self.check_tokens(cx, mac.tts.clone().into());
1490     }
1491     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: ast::Ident) {
1492         self.check_ident_token(cx, UnderMacro(false), ident);
1493     }
1494 }
1495
1496 declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
1497
1498 impl ExplicitOutlivesRequirements {
1499     fn lifetimes_outliving_lifetime<'tcx>(
1500         inferred_outlives: &'tcx [ty::Predicate<'tcx>],
1501         index: u32,
1502     ) -> Vec<ty::Region<'tcx>> {
1503         inferred_outlives.iter().filter_map(|pred| {
1504             match pred {
1505                 ty::Predicate::RegionOutlives(outlives) => {
1506                     let outlives = outlives.skip_binder();
1507                     match outlives.0 {
1508                         ty::ReEarlyBound(ebr) if ebr.index == index => {
1509                             Some(outlives.1)
1510                         }
1511                         _ => None,
1512                     }
1513                 }
1514                 _ => None
1515             }
1516         }).collect()
1517     }
1518
1519     fn lifetimes_outliving_type<'tcx>(
1520         inferred_outlives: &'tcx [ty::Predicate<'tcx>],
1521         index: u32,
1522     ) -> Vec<ty::Region<'tcx>> {
1523         inferred_outlives.iter().filter_map(|pred| {
1524             match pred {
1525                 ty::Predicate::TypeOutlives(outlives) => {
1526                     let outlives = outlives.skip_binder();
1527                     if outlives.0.is_param(index) {
1528                         Some(outlives.1)
1529                     } else {
1530                         None
1531                     }
1532                 }
1533                 _ => None
1534             }
1535         }).collect()
1536     }
1537
1538     fn collect_outlived_lifetimes<'tcx>(
1539         &self,
1540         param: &'tcx hir::GenericParam,
1541         tcx: TyCtxt<'tcx>,
1542         inferred_outlives: &'tcx [ty::Predicate<'tcx>],
1543         ty_generics: &'tcx ty::Generics,
1544     ) -> Vec<ty::Region<'tcx>> {
1545         let index = ty_generics.param_def_id_to_index[
1546             &tcx.hir().local_def_id(param.hir_id)];
1547
1548         match param.kind {
1549             hir::GenericParamKind::Lifetime { .. } => {
1550                 Self::lifetimes_outliving_lifetime(inferred_outlives, index)
1551             }
1552             hir::GenericParamKind::Type { .. } => {
1553                 Self::lifetimes_outliving_type(inferred_outlives, index)
1554             }
1555             hir::GenericParamKind::Const { .. } => Vec::new(),
1556         }
1557     }
1558
1559
1560     fn collect_outlives_bound_spans<'tcx>(
1561         &self,
1562         tcx: TyCtxt<'tcx>,
1563         bounds: &hir::GenericBounds,
1564         inferred_outlives: &[ty::Region<'tcx>],
1565         infer_static: bool,
1566     ) -> Vec<(usize, Span)> {
1567         use rustc::middle::resolve_lifetime::Region;
1568
1569         bounds
1570             .iter()
1571             .enumerate()
1572             .filter_map(|(i, bound)| {
1573                 if let hir::GenericBound::Outlives(lifetime) = bound {
1574                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
1575                         Some(Region::Static) if infer_static => {
1576                             inferred_outlives.iter()
1577                                 .any(|r| if let ty::ReStatic = r { true } else { false })
1578                         }
1579                         Some(Region::EarlyBound(index, ..)) => inferred_outlives
1580                             .iter()
1581                             .any(|r| {
1582                                 if let ty::ReEarlyBound(ebr) = r {
1583                                     ebr.index == index
1584                                 } else {
1585                                     false
1586                                 }
1587                             }),
1588                         _ => false,
1589                     };
1590                     if is_inferred {
1591                         Some((i, bound.span()))
1592                     } else {
1593                         None
1594                     }
1595                 } else {
1596                     None
1597                 }
1598             })
1599             .collect()
1600     }
1601
1602     fn consolidate_outlives_bound_spans(
1603         &self,
1604         lo: Span,
1605         bounds: &hir::GenericBounds,
1606         bound_spans: Vec<(usize, Span)>
1607     ) -> Vec<Span> {
1608         if bounds.is_empty() {
1609             return Vec::new();
1610         }
1611         if bound_spans.len() == bounds.len() {
1612             let (_, last_bound_span) = bound_spans[bound_spans.len()-1];
1613             // If all bounds are inferable, we want to delete the colon, so
1614             // start from just after the parameter (span passed as argument)
1615             vec![lo.to(last_bound_span)]
1616         } else {
1617             let mut merged = Vec::new();
1618             let mut last_merged_i = None;
1619
1620             let mut from_start = true;
1621             for (i, bound_span) in bound_spans {
1622                 match last_merged_i {
1623                     // If the first bound is inferable, our span should also eat the leading `+`.
1624                     None if i == 0 => {
1625                         merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
1626                         last_merged_i = Some(0);
1627                     },
1628                     // If consecutive bounds are inferable, merge their spans
1629                     Some(h) if i == h+1 => {
1630                         if let Some(tail) = merged.last_mut() {
1631                             // Also eat the trailing `+` if the first
1632                             // more-than-one bound is inferable
1633                             let to_span = if from_start && i < bounds.len() {
1634                                 bounds[i+1].span().shrink_to_lo()
1635                             } else {
1636                                 bound_span
1637                             };
1638                             *tail = tail.to(to_span);
1639                             last_merged_i = Some(i);
1640                         } else {
1641                             bug!("another bound-span visited earlier");
1642                         }
1643                     },
1644                     _ => {
1645                         // When we find a non-inferable bound, subsequent inferable bounds
1646                         // won't be consecutive from the start (and we'll eat the leading
1647                         // `+` rather than the trailing one)
1648                         from_start = false;
1649                         merged.push(bounds[i-1].span().shrink_to_hi().to(bound_span));
1650                         last_merged_i = Some(i);
1651                     }
1652                 }
1653             }
1654             merged
1655         }
1656     }
1657 }
1658
1659 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExplicitOutlivesRequirements {
1660     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
1661         use rustc::middle::resolve_lifetime::Region;
1662
1663         let infer_static = cx.tcx.features().infer_static_outlives_requirements;
1664         let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1665         if let hir::ItemKind::Struct(_, ref hir_generics)
1666             | hir::ItemKind::Enum(_, ref hir_generics)
1667             | hir::ItemKind::Union(_, ref hir_generics) = item.kind
1668         {
1669             let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
1670             if inferred_outlives.is_empty() {
1671                 return;
1672             }
1673
1674             let ty_generics = cx.tcx.generics_of(def_id);
1675
1676             let mut bound_count = 0;
1677             let mut lint_spans = Vec::new();
1678
1679             for param in &hir_generics.params {
1680                 let has_lifetime_bounds = param.bounds.iter().any(|bound| {
1681                     if let hir::GenericBound::Outlives(_) = bound {
1682                         true
1683                     } else {
1684                         false
1685                     }
1686                 });
1687                 if !has_lifetime_bounds {
1688                     continue;
1689                 }
1690
1691                 let relevant_lifetimes = self.collect_outlived_lifetimes(
1692                     param,
1693                     cx.tcx,
1694                     inferred_outlives,
1695                     ty_generics,
1696                 );
1697                 if relevant_lifetimes.is_empty() {
1698                     continue;
1699                 }
1700
1701                 let bound_spans = self.collect_outlives_bound_spans(
1702                     cx.tcx, &param.bounds, &relevant_lifetimes, infer_static,
1703                 );
1704                 bound_count += bound_spans.len();
1705                 lint_spans.extend(
1706                     self.consolidate_outlives_bound_spans(
1707                         param.span.shrink_to_hi(), &param.bounds, bound_spans
1708                     )
1709                 );
1710             }
1711
1712             let mut where_lint_spans = Vec::new();
1713             let mut dropped_predicate_count = 0;
1714             let num_predicates = hir_generics.where_clause.predicates.len();
1715             for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
1716                 let (relevant_lifetimes, bounds, span) = match where_predicate {
1717                     hir::WherePredicate::RegionPredicate(predicate) => {
1718                         if let Some(Region::EarlyBound(index, ..))
1719                             = cx.tcx.named_region(predicate.lifetime.hir_id)
1720                         {
1721                             (
1722                                 Self::lifetimes_outliving_lifetime(inferred_outlives, index),
1723                                 &predicate.bounds,
1724                                 predicate.span,
1725                             )
1726                         } else {
1727                             continue;
1728                         }
1729                     }
1730                     hir::WherePredicate::BoundPredicate(predicate) => {
1731                         // FIXME we can also infer bounds on associated types,
1732                         // and should check for them here.
1733                         match predicate.bounded_ty.kind {
1734                             hir::TyKind::Path(hir::QPath::Resolved(
1735                                 None,
1736                                 ref path,
1737                             )) => {
1738                                 if let Res::Def(DefKind::TyParam, def_id) = path.res {
1739                                     let index = ty_generics.param_def_id_to_index[&def_id];
1740                                     (
1741                                         Self::lifetimes_outliving_type(inferred_outlives, index),
1742                                         &predicate.bounds,
1743                                         predicate.span,
1744                                     )
1745                                 } else {
1746                                     continue;
1747                                 }
1748                             },
1749                             _ => { continue; }
1750                         }
1751                     }
1752                     _ => continue,
1753                 };
1754                 if relevant_lifetimes.is_empty() {
1755                     continue;
1756                 }
1757
1758                 let bound_spans = self.collect_outlives_bound_spans(
1759                     cx.tcx, bounds, &relevant_lifetimes, infer_static,
1760                 );
1761                 bound_count += bound_spans.len();
1762
1763                 let drop_predicate = bound_spans.len() == bounds.len();
1764                 if drop_predicate {
1765                     dropped_predicate_count += 1;
1766                 }
1767
1768                 // If all the bounds on a predicate were inferable and there are
1769                 // further predicates, we want to eat the trailing comma.
1770                 if drop_predicate && i + 1 < num_predicates {
1771                     let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
1772                     where_lint_spans.push(
1773                         span.to(next_predicate_span.shrink_to_lo())
1774                     );
1775                 } else {
1776                     where_lint_spans.extend(
1777                         self.consolidate_outlives_bound_spans(
1778                             span.shrink_to_lo(),
1779                             bounds,
1780                             bound_spans
1781                         )
1782                     );
1783                 }
1784             }
1785
1786             // If all predicates are inferable, drop the entire clause
1787             // (including the `where`)
1788             if num_predicates > 0 && dropped_predicate_count == num_predicates {
1789                 let where_span = hir_generics.where_clause.span()
1790                     .expect("span of (nonempty) where clause should exist");
1791                 // Extend the where clause back to the closing `>` of the
1792                 // generics, except for tuple struct, which have the `where`
1793                 // after the fields of the struct.
1794                 let full_where_span = if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _)
1795                         = item.kind
1796                 {
1797                     where_span
1798                 } else {
1799                     hir_generics.span.shrink_to_hi().to(where_span)
1800                 };
1801                 lint_spans.push(
1802                     full_where_span
1803                 );
1804             } else {
1805                 lint_spans.extend(where_lint_spans);
1806             }
1807
1808             if !lint_spans.is_empty() {
1809                 let mut err = cx.struct_span_lint(
1810                     EXPLICIT_OUTLIVES_REQUIREMENTS,
1811                     lint_spans.clone(),
1812                     "outlives requirements can be inferred"
1813                 );
1814                 err.multipart_suggestion(
1815                     if bound_count == 1 {
1816                         "remove this bound"
1817                     } else {
1818                         "remove these bounds"
1819                     },
1820                     lint_spans.into_iter().map(|span| (span, "".to_owned())).collect::<Vec<_>>(),
1821                     Applicability::MachineApplicable
1822                 );
1823                 err.emit();
1824             }
1825         }
1826     }
1827 }
1828
1829 declare_lint! {
1830     pub INCOMPLETE_FEATURES,
1831     Warn,
1832     "incomplete features that may function improperly in some or all cases"
1833 }
1834
1835 declare_lint_pass!(
1836     /// Check for used feature gates in `INCOMPLETE_FEATURES` in `feature_gate.rs`.
1837     IncompleteFeatures => [INCOMPLETE_FEATURES]
1838 );
1839
1840 impl EarlyLintPass for IncompleteFeatures {
1841     fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
1842         let features = cx.sess.features_untracked();
1843         features.declared_lang_features
1844             .iter().map(|(name, span, _)| (name, span))
1845             .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
1846             .filter(|(name, _)| feature_gate::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
1847             .for_each(|(name, &span)| {
1848                 cx.struct_span_lint(
1849                     INCOMPLETE_FEATURES,
1850                     span,
1851                     &format!(
1852                         "the feature `{}` is incomplete and may cause the compiler to crash",
1853                         name,
1854                     )
1855                 )
1856                 .emit();
1857             });
1858     }
1859 }
1860
1861 declare_lint! {
1862     pub INVALID_VALUE,
1863     Warn,
1864     "an invalid value is being created (such as a NULL reference)"
1865 }
1866
1867 declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
1868
1869 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidValue {
1870     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &hir::Expr) {
1871
1872         #[derive(Debug, Copy, Clone, PartialEq)]
1873         enum InitKind { Zeroed, Uninit };
1874
1875         /// Information about why a type cannot be initialized this way.
1876         /// Contains an error message and optionally a span to point at.
1877         type InitError = (String, Option<Span>);
1878
1879         /// Test if this constant is all-0.
1880         fn is_zero(expr: &hir::Expr) -> bool {
1881             use hir::ExprKind::*;
1882             use syntax::ast::LitKind::*;
1883             match &expr.kind {
1884                 Lit(lit) =>
1885                     if let Int(i, _) = lit.node {
1886                         i == 0
1887                     } else {
1888                         false
1889                     },
1890                 Tup(tup) =>
1891                     tup.iter().all(is_zero),
1892                 _ =>
1893                     false
1894             }
1895         }
1896
1897         /// Determine if this expression is a "dangerous initialization".
1898         fn is_dangerous_init(cx: &LateContext<'_, '_>, expr: &hir::Expr) -> Option<InitKind> {
1899             const ZEROED_PATH: &[Symbol] = &[sym::core, sym::mem, sym::zeroed];
1900             const UININIT_PATH: &[Symbol] = &[sym::core, sym::mem, sym::uninitialized];
1901             // `transmute` is inside an anonymous module (the `extern` block?);
1902             // `Invalid` represents the empty string and matches that.
1903             const TRANSMUTE_PATH: &[Symbol] =
1904                 &[sym::core, sym::intrinsics, kw::Invalid, sym::transmute];
1905
1906             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
1907                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
1908                     let def_id = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
1909
1910                     if cx.match_def_path(def_id, ZEROED_PATH) {
1911                         return Some(InitKind::Zeroed);
1912                     }
1913                     if cx.match_def_path(def_id, UININIT_PATH) {
1914                         return Some(InitKind::Uninit);
1915                     }
1916                     if cx.match_def_path(def_id, TRANSMUTE_PATH) {
1917                         if is_zero(&args[0]) {
1918                             return Some(InitKind::Zeroed);
1919                         }
1920                     }
1921                     // FIXME: Also detect `MaybeUninit::zeroed().assume_init()` and
1922                     // `MaybeUninit::uninit().assume_init()`.
1923                 }
1924             }
1925
1926             None
1927         }
1928
1929         /// Return `Some` only if we are sure this type does *not*
1930         /// allow zero initialization.
1931         fn ty_find_init_error<'tcx>(
1932             tcx: TyCtxt<'tcx>,
1933             ty: Ty<'tcx>,
1934             init: InitKind,
1935         ) -> Option<InitError> {
1936             use rustc::ty::TyKind::*;
1937             match ty.kind {
1938                 // Primitive types that don't like 0 as a value.
1939                 Ref(..) => Some((format!("References must be non-null"), None)),
1940                 Adt(..) if ty.is_box() => Some((format!("`Box` must be non-null"), None)),
1941                 FnPtr(..) => Some((format!("Function pointers must be non-null"), None)),
1942                 Never => Some((format!("The never type (`!`) has no valid value"), None)),
1943                 // Primitive types with other constraints.
1944                 Bool if init == InitKind::Uninit =>
1945                     Some((format!("Booleans must be `true` or `false`"), None)),
1946                 Char if init == InitKind::Uninit =>
1947                     Some((format!("Characters must be a valid unicode codepoint"), None)),
1948                 // Recurse and checks for some compound types.
1949                 Adt(adt_def, substs) if !adt_def.is_union() => {
1950                     // First check f this ADT has a layout attribute (like `NonNull` and friends).
1951                     use std::ops::Bound;
1952                     match tcx.layout_scalar_valid_range(adt_def.did) {
1953                         // We exploit here that `layout_scalar_valid_range` will never
1954                         // return `Bound::Excluded`.  (And we have tests checking that we
1955                         // handle the attribute correctly.)
1956                         (Bound::Included(lo), _) if lo > 0 =>
1957                             return Some((format!("{} must be non-null", ty), None)),
1958                         (Bound::Included(_), _) | (_, Bound::Included(_))
1959                         if init == InitKind::Uninit =>
1960                             return Some((
1961                                 format!("{} must be initialized inside its custom valid range", ty),
1962                                 None,
1963                             )),
1964                         _ => {}
1965                     }
1966                     // Now, recurse.
1967                     match adt_def.variants.len() {
1968                         0 => Some((format!("0-variant enums have no valid value"), None)),
1969                         1 => {
1970                             // Struct, or enum with exactly one variant.
1971                             // Proceed recursively, check all fields.
1972                             let variant = &adt_def.variants[VariantIdx::from_u32(0)];
1973                             variant.fields.iter().find_map(|field| {
1974                                 ty_find_init_error(
1975                                     tcx,
1976                                     field.ty(tcx, substs),
1977                                     init,
1978                                 ).map(|(mut msg, span)| if span.is_none() {
1979                                     // Point to this field, should be helpful for figuring
1980                                     // out where the source of the error is.
1981                                     let span = tcx.def_span(field.did);
1982                                     write!(&mut msg, " (in this {} field)", adt_def.descr())
1983                                         .unwrap();
1984                                     (msg, Some(span))
1985                                 } else {
1986                                     // Just forward.
1987                                     (msg, span)
1988                                 })
1989                             })
1990                         }
1991                         // Multi-variant enums are tricky: if all but one variant are
1992                         // uninhabited, we might actually do layout like for a single-variant
1993                         // enum, and then even leaving them uninitialized could be okay.
1994                         _ => None, // Conservative fallback for multi-variant enum.
1995                     }
1996                 }
1997                 Tuple(..) => {
1998                     // Proceed recursively, check all fields.
1999                     ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
2000                 }
2001                 // Conservative fallback.
2002                 _ => None,
2003             }
2004         }
2005
2006         if let Some(init) = is_dangerous_init(cx, expr) {
2007             // This conjures an instance of a type out of nothing,
2008             // using zeroed or uninitialized memory.
2009             // We are extremely conservative with what we warn about.
2010             let conjured_ty = cx.tables.expr_ty(expr);
2011             if let Some((msg, span)) = ty_find_init_error(cx.tcx, conjured_ty, init) {
2012                 let mut err = cx.struct_span_lint(
2013                     INVALID_VALUE,
2014                     expr.span,
2015                     &format!(
2016                         "the type `{}` does not permit {}",
2017                         conjured_ty,
2018                         match init {
2019                             InitKind::Zeroed => "zero-initialization",
2020                             InitKind::Uninit => "being left uninitialized",
2021                         },
2022                     ),
2023                 );
2024                 err.span_label(expr.span,
2025                     "this code causes undefined behavior when executed");
2026                 err.span_label(expr.span, "help: use `MaybeUninit<T>` instead");
2027                 if let Some(span) = span {
2028                     err.span_note(span, &msg);
2029                 } else {
2030                     err.note(&msg);
2031                 }
2032                 err.emit();
2033             }
2034         }
2035     }
2036 }