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