clippy_lints/src/utils/internal_lints.rs

   1 use clippy_utils::consts::{constant_simple, Constant};
   2 use clippy_utils::diagnostics::{span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then};
   3 use clippy_utils::macros::root_macro_call_first_node;
   4 use clippy_utils::source::snippet;
   5 use clippy_utils::ty::match_type;
   6 use clippy_utils::{
   7     def_path_res, higher, is_else_clause, is_expn_of, is_expr_path_def_path, is_lint_allowed, match_def_path,
   8     method_calls, paths, peel_blocks_with_stmt, SpanlessEq,
   9 };
  10 use if_chain::if_chain;
  11 use rustc_ast as ast;
  12 use rustc_ast::ast::{Crate, ItemKind, LitKind, ModKind, NodeId};
  13 use rustc_ast::visit::FnKind;
  14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  15 use rustc_errors::Applicability;
  16 use rustc_hir as hir;
  17 use rustc_hir::def::{DefKind, Res};
  18 use rustc_hir::def_id::DefId;
  19 use rustc_hir::hir_id::CRATE_HIR_ID;
  20 use rustc_hir::intravisit::Visitor;
  21 use rustc_hir::{
  22     BinOpKind, Block, Expr, ExprKind, HirId, Item, Local, MutTy, Mutability, Node, Path, Stmt, StmtKind, Ty, TyKind,
  23     UnOp,
  24 };
  25 use rustc_lint::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
  26 use rustc_middle::hir::nested_filter;
  27 use rustc_middle::mir::interpret::ConstValue;
  28 use rustc_middle::ty::{self, fast_reject::SimplifiedTypeGen, subst::GenericArgKind, FloatTy};
  29 use rustc_semver::RustcVersion;
  30 use rustc_session::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
  31 use rustc_span::source_map::Spanned;
  32 use rustc_span::symbol::Symbol;
  33 use rustc_span::{sym, BytePos, Span};
  34 use rustc_typeck::hir_ty_to_ty;
  35
  36 use std::borrow::{Borrow, Cow};
  37
  38 #[cfg(feature = "internal")]
  39 pub mod metadata_collector;
  40
  41 declare_clippy_lint! {
  42     /// ### What it does
  43     /// Checks for various things we like to keep tidy in clippy.
  44     ///
  45     /// ### Why is this bad?
  46     /// We like to pretend we're an example of tidy code.
  47     ///
  48     /// ### Example
  49     /// Wrong ordering of the util::paths constants.
  50     pub CLIPPY_LINTS_INTERNAL,
  51     internal,
  52     "various things that will negatively affect your clippy experience"
  53 }
  54
  55 declare_clippy_lint! {
  56     /// ### What it does
  57     /// Ensures every lint is associated to a `LintPass`.
  58     ///
  59     /// ### Why is this bad?
  60     /// The compiler only knows lints via a `LintPass`. Without
  61     /// putting a lint to a `LintPass::get_lints()`'s return, the compiler will not
  62     /// know the name of the lint.
  63     ///
  64     /// ### Known problems
  65     /// Only checks for lints associated using the
  66     /// `declare_lint_pass!`, `impl_lint_pass!`, and `lint_array!` macros.
  67     ///
  68     /// ### Example
  69     /// ```rust,ignore
  70     /// declare_lint! { pub LINT_1, ... }
  71     /// declare_lint! { pub LINT_2, ... }
  72     /// declare_lint! { pub FORGOTTEN_LINT, ... }
  73     /// // ...
  74     /// declare_lint_pass!(Pass => [LINT_1, LINT_2]);
  75     /// // missing FORGOTTEN_LINT
  76     /// ```
  77     pub LINT_WITHOUT_LINT_PASS,
  78     internal,
  79     "declaring a lint without associating it in a LintPass"
  80 }
  81
  82 declare_clippy_lint! {
  83     /// ### What it does
  84     /// Checks for calls to `cx.span_lint*` and suggests to use the `utils::*`
  85     /// variant of the function.
  86     ///
  87     /// ### Why is this bad?
  88     /// The `utils::*` variants also add a link to the Clippy documentation to the
  89     /// warning/error messages.
  90     ///
  91     /// ### Example
  92     /// Bad:
  93     /// ```rust,ignore
  94     /// cx.span_lint(LINT_NAME, "message");
  95     /// ```
  96     ///
  97     /// Good:
  98     /// ```rust,ignore
  99     /// utils::span_lint(cx, LINT_NAME, "message");
 100     /// ```
 101     pub COMPILER_LINT_FUNCTIONS,
 102     internal,
 103     "usage of the lint functions of the compiler instead of the utils::* variant"
 104 }
 105
 106 declare_clippy_lint! {
 107     /// ### What it does
 108     /// Checks for calls to `cx.outer().expn_data()` and suggests to use
 109     /// the `cx.outer_expn_data()`
 110     ///
 111     /// ### Why is this bad?
 112     /// `cx.outer_expn_data()` is faster and more concise.
 113     ///
 114     /// ### Example
 115     /// Bad:
 116     /// ```rust,ignore
 117     /// expr.span.ctxt().outer().expn_data()
 118     /// ```
 119     ///
 120     /// Good:
 121     /// ```rust,ignore
 122     /// expr.span.ctxt().outer_expn_data()
 123     /// ```
 124     pub OUTER_EXPN_EXPN_DATA,
 125     internal,
 126     "using `cx.outer_expn().expn_data()` instead of `cx.outer_expn_data()`"
 127 }
 128
 129 declare_clippy_lint! {
 130     /// ### What it does
 131     /// Not an actual lint. This lint is only meant for testing our customized internal compiler
 132     /// error message by calling `panic`.
 133     ///
 134     /// ### Why is this bad?
 135     /// ICE in large quantities can damage your teeth
 136     ///
 137     /// ### Example
 138     /// Bad:
 139     /// ```rust,ignore
 140     /// 🍦🍦🍦🍦🍦
 141     /// ```
 142     pub PRODUCE_ICE,
 143     internal,
 144     "this message should not appear anywhere as we ICE before and don't emit the lint"
 145 }
 146
 147 declare_clippy_lint! {
 148     /// ### What it does
 149     /// Checks for cases of an auto-generated lint without an updated description,
 150     /// i.e. `default lint description`.
 151     ///
 152     /// ### Why is this bad?
 153     /// Indicates that the lint is not finished.
 154     ///
 155     /// ### Example
 156     /// Bad:
 157     /// ```rust,ignore
 158     /// declare_lint! { pub COOL_LINT, nursery, "default lint description" }
 159     /// ```
 160     ///
 161     /// Good:
 162     /// ```rust,ignore
 163     /// declare_lint! { pub COOL_LINT, nursery, "a great new lint" }
 164     /// ```
 165     pub DEFAULT_LINT,
 166     internal,
 167     "found 'default lint description' in a lint declaration"
 168 }
 169
 170 declare_clippy_lint! {
 171     /// ### What it does
 172     /// Lints `span_lint_and_then` function calls, where the
 173     /// closure argument has only one statement and that statement is a method
 174     /// call to `span_suggestion`, `span_help`, `span_note` (using the same
 175     /// span), `help` or `note`.
 176     ///
 177     /// These usages of `span_lint_and_then` should be replaced with one of the
 178     /// wrapper functions `span_lint_and_sugg`, span_lint_and_help`, or
 179     /// `span_lint_and_note`.
 180     ///
 181     /// ### Why is this bad?
 182     /// Using the wrapper `span_lint_and_*` functions, is more
 183     /// convenient, readable and less error prone.
 184     ///
 185     /// ### Example
 186     /// Bad:
 187     /// ```rust,ignore
 188     /// span_lint_and_then(cx, TEST_LINT, expr.span, lint_msg, |diag| {
 189     ///     diag.span_suggestion(
 190     ///         expr.span,
 191     ///         help_msg,
 192     ///         sugg.to_string(),
 193     ///         Applicability::MachineApplicable,
 194     ///     );
 195     /// });
 196     /// span_lint_and_then(cx, TEST_LINT, expr.span, lint_msg, |diag| {
 197     ///     diag.span_help(expr.span, help_msg);
 198     /// });
 199     /// span_lint_and_then(cx, TEST_LINT, expr.span, lint_msg, |diag| {
 200     ///     diag.help(help_msg);
 201     /// });
 202     /// span_lint_and_then(cx, TEST_LINT, expr.span, lint_msg, |diag| {
 203     ///     diag.span_note(expr.span, note_msg);
 204     /// });
 205     /// span_lint_and_then(cx, TEST_LINT, expr.span, lint_msg, |diag| {
 206     ///     diag.note(note_msg);
 207     /// });
 208     /// ```
 209     ///
 210     /// Good:
 211     /// ```rust,ignore
 212     /// span_lint_and_sugg(
 213     ///     cx,
 214     ///     TEST_LINT,
 215     ///     expr.span,
 216     ///     lint_msg,
 217     ///     help_msg,
 218     ///     sugg.to_string(),
 219     ///     Applicability::MachineApplicable,
 220     /// );
 221     /// span_lint_and_help(cx, TEST_LINT, expr.span, lint_msg, Some(expr.span), help_msg);
 222     /// span_lint_and_help(cx, TEST_LINT, expr.span, lint_msg, None, help_msg);
 223     /// span_lint_and_note(cx, TEST_LINT, expr.span, lint_msg, Some(expr.span), note_msg);
 224     /// span_lint_and_note(cx, TEST_LINT, expr.span, lint_msg, None, note_msg);
 225     /// ```
 226     pub COLLAPSIBLE_SPAN_LINT_CALLS,
 227     internal,
 228     "found collapsible `span_lint_and_then` calls"
 229 }
 230
 231 declare_clippy_lint! {
 232     /// ### What it does
 233     /// Checks for calls to `utils::match_type()` on a type diagnostic item
 234     /// and suggests to use `utils::is_type_diagnostic_item()` instead.
 235     ///
 236     /// ### Why is this bad?
 237     /// `utils::is_type_diagnostic_item()` does not require hardcoded paths.
 238     ///
 239     /// ### Example
 240     /// Bad:
 241     /// ```rust,ignore
 242     /// utils::match_type(cx, ty, &paths::VEC)
 243     /// ```
 244     ///
 245     /// Good:
 246     /// ```rust,ignore
 247     /// utils::is_type_diagnostic_item(cx, ty, sym::Vec)
 248     /// ```
 249     pub MATCH_TYPE_ON_DIAGNOSTIC_ITEM,
 250     internal,
 251     "using `utils::match_type()` instead of `utils::is_type_diagnostic_item()`"
 252 }
 253
 254 declare_clippy_lint! {
 255     /// ### What it does
 256     /// Checks the paths module for invalid paths.
 257     ///
 258     /// ### Why is this bad?
 259     /// It indicates a bug in the code.
 260     ///
 261     /// ### Example
 262     /// None.
 263     pub INVALID_PATHS,
 264     internal,
 265     "invalid path"
 266 }
 267
 268 declare_clippy_lint! {
 269     /// ### What it does
 270     /// Checks for interning symbols that have already been pre-interned and defined as constants.
 271     ///
 272     /// ### Why is this bad?
 273     /// It's faster and easier to use the symbol constant.
 274     ///
 275     /// ### Example
 276     /// Bad:
 277     /// ```rust,ignore
 278     /// let _ = sym!(f32);
 279     /// ```
 280     ///
 281     /// Good:
 282     /// ```rust,ignore
 283     /// let _ = sym::f32;
 284     /// ```
 285     pub INTERNING_DEFINED_SYMBOL,
 286     internal,
 287     "interning a symbol that is pre-interned and defined as a constant"
 288 }
 289
 290 declare_clippy_lint! {
 291     /// ### What it does
 292     /// Checks for unnecessary conversion from Symbol to a string.
 293     ///
 294     /// ### Why is this bad?
 295     /// It's faster use symbols directly intead of strings.
 296     ///
 297     /// ### Example
 298     /// Bad:
 299     /// ```rust,ignore
 300     /// symbol.as_str() == "clippy";
 301     /// ```
 302     ///
 303     /// Good:
 304     /// ```rust,ignore
 305     /// symbol == sym::clippy;
 306     /// ```
 307     pub UNNECESSARY_SYMBOL_STR,
 308     internal,
 309     "unnecessary conversion between Symbol and string"
 310 }
 311
 312 declare_clippy_lint! {
 313     /// Finds unidiomatic usage of `if_chain!`
 314     pub IF_CHAIN_STYLE,
 315     internal,
 316     "non-idiomatic `if_chain!` usage"
 317 }
 318
 319 declare_clippy_lint! {
 320     /// ### What it does
 321     /// Checks for invalid `clippy::version` attributes.
 322     ///
 323     /// Valid values are:
 324     /// * "pre 1.29.0"
 325     /// * any valid semantic version
 326     pub INVALID_CLIPPY_VERSION_ATTRIBUTE,
 327     internal,
 328     "found an invalid `clippy::version` attribute"
 329 }
 330
 331 declare_clippy_lint! {
 332     /// ### What it does
 333     /// Checks for declared clippy lints without the `clippy::version` attribute.
 334     ///
 335     pub MISSING_CLIPPY_VERSION_ATTRIBUTE,
 336     internal,
 337     "found clippy lint without `clippy::version` attribute"
 338 }
 339
 340 declare_clippy_lint! {
 341     /// ### What it does
 342     /// Check that the `extract_msrv_attr!` macro is used, when a lint has a MSRV.
 343     ///
 344     pub MISSING_MSRV_ATTR_IMPL,
 345     internal,
 346     "checking if all necessary steps were taken when adding a MSRV to a lint"
 347 }
 348
 349 declare_lint_pass!(ClippyLintsInternal => [CLIPPY_LINTS_INTERNAL]);
 350
 351 impl EarlyLintPass for ClippyLintsInternal {
 352     fn check_crate(&mut self, cx: &EarlyContext<'_>, krate: &Crate) {
 353         if let Some(utils) = krate.items.iter().find(|item| item.ident.name.as_str() == "utils") {
 354             if let ItemKind::Mod(_, ModKind::Loaded(ref items, ..)) = utils.kind {
 355                 if let Some(paths) = items.iter().find(|item| item.ident.name.as_str() == "paths") {
 356                     if let ItemKind::Mod(_, ModKind::Loaded(ref items, ..)) = paths.kind {
 357                         let mut last_name: Option<&str> = None;
 358                         for item in items {
 359                             let name = item.ident.as_str();
 360                             if let Some(last_name) = last_name {
 361                                 if *last_name > *name {
 362                                     span_lint(
 363                                         cx,
 364                                         CLIPPY_LINTS_INTERNAL,
 365                                         item.span,
 366                                         "this constant should be before the previous constant due to lexical \
 367                                          ordering",
 368                                     );
 369                                 }
 370                             }
 371                             last_name = Some(name);
 372                         }
 373                     }
 374                 }
 375             }
 376         }
 377     }
 378 }
 379
 380 #[derive(Clone, Debug, Default)]
 381 pub struct LintWithoutLintPass {
 382     declared_lints: FxHashMap<Symbol, Span>,
 383     registered_lints: FxHashSet<Symbol>,
 384 }
 385
 386 impl_lint_pass!(LintWithoutLintPass => [DEFAULT_LINT, LINT_WITHOUT_LINT_PASS, INVALID_CLIPPY_VERSION_ATTRIBUTE, MISSING_CLIPPY_VERSION_ATTRIBUTE]);
 387
 388 impl<'tcx> LateLintPass<'tcx> for LintWithoutLintPass {
 389     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 390         if is_lint_allowed(cx, DEFAULT_LINT, item.hir_id()) {
 391             return;
 392         }
 393
 394         if let hir::ItemKind::Static(ty, Mutability::Not, body_id) = item.kind {
 395             if is_lint_ref_type(cx, ty) {
 396                 check_invalid_clippy_version_attribute(cx, item);
 397
 398                 let expr = &cx.tcx.hir().body(body_id).value;
 399                 if_chain! {
 400                     if let ExprKind::AddrOf(_, _, inner_exp) = expr.kind;
 401                     if let ExprKind::Struct(_, fields, _) = inner_exp.kind;
 402                     let field = fields
 403                         .iter()
 404                         .find(|f| f.ident.as_str() == "desc")
 405                         .expect("lints must have a description field");
 406                     if let ExprKind::Lit(Spanned {
 407                         node: LitKind::Str(ref sym, _),
 408                         ..
 409                     }) = field.expr.kind;
 410                     if sym.as_str() == "default lint description";
 411
 412                     then {
 413                         span_lint(
 414                             cx,
 415                             DEFAULT_LINT,
 416                             item.span,
 417                             &format!("the lint `{}` has the default lint description", item.ident.name),
 418                         );
 419                     }
 420                 }
 421                 self.declared_lints.insert(item.ident.name, item.span);
 422             }
 423         } else if let Some(macro_call) = root_macro_call_first_node(cx, item) {
 424             if !matches!(
 425                 &*cx.tcx.item_name(macro_call.def_id).as_str(),
 426                 "impl_lint_pass" | "declare_lint_pass"
 427             ) {
 428                 return;
 429             }
 430             if let hir::ItemKind::Impl(hir::Impl {
 431                 of_trait: None,
 432                 items: impl_item_refs,
 433                 ..
 434             }) = item.kind
 435             {
 436                 let mut collector = LintCollector {
 437                     output: &mut self.registered_lints,
 438                     cx,
 439                 };
 440                 let body_id = cx.tcx.hir().body_owned_by(
 441                     impl_item_refs
 442                         .iter()
 443                         .find(|iiref| iiref.ident.as_str() == "get_lints")
 444                         .expect("LintPass needs to implement get_lints")
 445                         .id
 446                         .hir_id(),
 447                 );
 448                 collector.visit_expr(&cx.tcx.hir().body(body_id).value);
 449             }
 450         }
 451     }
 452
 453     fn check_crate_post(&mut self, cx: &LateContext<'tcx>) {
 454         if is_lint_allowed(cx, LINT_WITHOUT_LINT_PASS, CRATE_HIR_ID) {
 455             return;
 456         }
 457
 458         for (lint_name, &lint_span) in &self.declared_lints {
 459             // When using the `declare_tool_lint!` macro, the original `lint_span`'s
 460             // file points to "<rustc macros>".
 461             // `compiletest-rs` thinks that's an error in a different file and
 462             // just ignores it. This causes the test in compile-fail/lint_pass
 463             // not able to capture the error.
 464             // Therefore, we need to climb the macro expansion tree and find the
 465             // actual span that invoked `declare_tool_lint!`:
 466             let lint_span = lint_span.ctxt().outer_expn_data().call_site;
 467
 468             if !self.registered_lints.contains(lint_name) {
 469                 span_lint(
 470                     cx,
 471                     LINT_WITHOUT_LINT_PASS,
 472                     lint_span,
 473                     &format!("the lint `{}` is not added to any `LintPass`", lint_name),
 474                 );
 475             }
 476         }
 477     }
 478 }
 479
 480 fn is_lint_ref_type<'tcx>(cx: &LateContext<'tcx>, ty: &Ty<'_>) -> bool {
 481     if let TyKind::Rptr(
 482         _,
 483         MutTy {
 484             ty: inner,
 485             mutbl: Mutability::Not,
 486         },
 487     ) = ty.kind
 488     {
 489         if let TyKind::Path(ref path) = inner.kind {
 490             if let Res::Def(DefKind::Struct, def_id) = cx.qpath_res(path, inner.hir_id) {
 491                 return match_def_path(cx, def_id, &paths::LINT);
 492             }
 493         }
 494     }
 495
 496     false
 497 }
 498
 499 fn check_invalid_clippy_version_attribute(cx: &LateContext<'_>, item: &'_ Item<'_>) {
 500     if let Some(value) = extract_clippy_version_value(cx, item) {
 501         // The `sym!` macro doesn't work as it only expects a single token.
 502         // It's better to keep it this way and have a direct `Symbol::intern` call here.
 503         if value == Symbol::intern("pre 1.29.0") {
 504             return;
 505         }
 506
 507         if RustcVersion::parse(&*value.as_str()).is_err() {
 508             span_lint_and_help(
 509                 cx,
 510                 INVALID_CLIPPY_VERSION_ATTRIBUTE,
 511                 item.span,
 512                 "this item has an invalid `clippy::version` attribute",
 513                 None,
 514                 "please use a valid sematic version, see `doc/adding_lints.md`",
 515             );
 516         }
 517     } else {
 518         span_lint_and_help(
 519             cx,
 520             MISSING_CLIPPY_VERSION_ATTRIBUTE,
 521             item.span,
 522             "this lint is missing the `clippy::version` attribute or version value",
 523             None,
 524             "please use a `clippy::version` attribute, see `doc/adding_lints.md`",
 525         );
 526     }
 527 }
 528
 529 /// This function extracts the version value of a `clippy::version` attribute if the given value has
 530 /// one
 531 fn extract_clippy_version_value(cx: &LateContext<'_>, item: &'_ Item<'_>) -> Option<Symbol> {
 532     let attrs = cx.tcx.hir().attrs(item.hir_id());
 533     attrs.iter().find_map(|attr| {
 534         if_chain! {
 535             // Identify attribute
 536             if let ast::AttrKind::Normal(ref attr_kind, _) = &attr.kind;
 537             if let [tool_name, attr_name] = &attr_kind.path.segments[..];
 538             if tool_name.ident.name == sym::clippy;
 539             if attr_name.ident.name == sym::version;
 540             if let Some(version) = attr.value_str();
 541             then {
 542                 Some(version)
 543             } else {
 544                 None
 545             }
 546         }
 547     })
 548 }
 549
 550 struct LintCollector<'a, 'tcx> {
 551     output: &'a mut FxHashSet<Symbol>,
 552     cx: &'a LateContext<'tcx>,
 553 }
 554
 555 impl<'a, 'tcx> Visitor<'tcx> for LintCollector<'a, 'tcx> {
 556     type NestedFilter = nested_filter::All;
 557
 558     fn visit_path(&mut self, path: &'tcx Path<'_>, _: HirId) {
 559         if path.segments.len() == 1 {
 560             self.output.insert(path.segments[0].ident.name);
 561         }
 562     }
 563
 564     fn nested_visit_map(&mut self) -> Self::Map {
 565         self.cx.tcx.hir()
 566     }
 567 }
 568
 569 #[derive(Clone, Default)]
 570 pub struct CompilerLintFunctions {
 571     map: FxHashMap<&'static str, &'static str>,
 572 }
 573
 574 impl CompilerLintFunctions {
 575     #[must_use]
 576     pub fn new() -> Self {
 577         let mut map = FxHashMap::default();
 578         map.insert("span_lint", "utils::span_lint");
 579         map.insert("struct_span_lint", "utils::span_lint");
 580         map.insert("lint", "utils::span_lint");
 581         map.insert("span_lint_note", "utils::span_lint_and_note");
 582         map.insert("span_lint_help", "utils::span_lint_and_help");
 583         Self { map }
 584     }
 585 }
 586
 587 impl_lint_pass!(CompilerLintFunctions => [COMPILER_LINT_FUNCTIONS]);
 588
 589 impl<'tcx> LateLintPass<'tcx> for CompilerLintFunctions {
 590     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 591         if is_lint_allowed(cx, COMPILER_LINT_FUNCTIONS, expr.hir_id) {
 592             return;
 593         }
 594
 595         if_chain! {
 596             if let ExprKind::MethodCall(path, [self_arg, ..], _) = &expr.kind;
 597             let fn_name = path.ident;
 598             if let Some(sugg) = self.map.get(&*fn_name.as_str());
 599             let ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
 600             if match_type(cx, ty, &paths::EARLY_CONTEXT)
 601                 || match_type(cx, ty, &paths::LATE_CONTEXT);
 602             then {
 603                 span_lint_and_help(
 604                     cx,
 605                     COMPILER_LINT_FUNCTIONS,
 606                     path.ident.span,
 607                     "usage of a compiler lint function",
 608                     None,
 609                     &format!("please use the Clippy variant of this function: `{}`", sugg),
 610                 );
 611             }
 612         }
 613     }
 614 }
 615
 616 declare_lint_pass!(OuterExpnDataPass => [OUTER_EXPN_EXPN_DATA]);
 617
 618 impl<'tcx> LateLintPass<'tcx> for OuterExpnDataPass {
 619     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
 620         if is_lint_allowed(cx, OUTER_EXPN_EXPN_DATA, expr.hir_id) {
 621             return;
 622         }
 623
 624         let (method_names, arg_lists, spans) = method_calls(expr, 2);
 625         let method_names: Vec<&str> = method_names.iter().map(Symbol::as_str).collect();
 626         if_chain! {
 627             if let ["expn_data", "outer_expn"] = method_names.as_slice();
 628             let args = arg_lists[1];
 629             if args.len() == 1;
 630             let self_arg = &args[0];
 631             let self_ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
 632             if match_type(cx, self_ty, &paths::SYNTAX_CONTEXT);
 633             then {
 634                 span_lint_and_sugg(
 635                     cx,
 636                     OUTER_EXPN_EXPN_DATA,
 637                     spans[1].with_hi(expr.span.hi()),
 638                     "usage of `outer_expn().expn_data()`",
 639                     "try",
 640                     "outer_expn_data()".to_string(),
 641                     Applicability::MachineApplicable,
 642                 );
 643             }
 644         }
 645     }
 646 }
 647
 648 declare_lint_pass!(ProduceIce => [PRODUCE_ICE]);
 649
 650 impl EarlyLintPass for ProduceIce {
 651     fn check_fn(&mut self, _: &EarlyContext<'_>, fn_kind: FnKind<'_>, _: Span, _: NodeId) {
 652         assert!(!is_trigger_fn(fn_kind), "Would you like some help with that?");
 653     }
 654 }
 655
 656 fn is_trigger_fn(fn_kind: FnKind<'_>) -> bool {
 657     match fn_kind {
 658         FnKind::Fn(_, ident, ..) => ident.name.as_str() == "it_looks_like_you_are_trying_to_kill_clippy",
 659         FnKind::Closure(..) => false,
 660     }
 661 }
 662
 663 declare_lint_pass!(CollapsibleCalls => [COLLAPSIBLE_SPAN_LINT_CALLS]);
 664
 665 impl<'tcx> LateLintPass<'tcx> for CollapsibleCalls {
 666     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
 667         if is_lint_allowed(cx, COLLAPSIBLE_SPAN_LINT_CALLS, expr.hir_id) {
 668             return;
 669         }
 670
 671         if_chain! {
 672             if let ExprKind::Call(func, and_then_args) = expr.kind;
 673             if is_expr_path_def_path(cx, func, &["clippy_utils", "diagnostics", "span_lint_and_then"]);
 674             if and_then_args.len() == 5;
 675             if let ExprKind::Closure(_, _, body_id, _, _) = &and_then_args[4].kind;
 676             let body = cx.tcx.hir().body(*body_id);
 677             let only_expr = peel_blocks_with_stmt(&body.value);
 678             if let ExprKind::MethodCall(ps, span_call_args, _) = &only_expr.kind;
 679             then {
 680                 let and_then_snippets = get_and_then_snippets(cx, and_then_args);
 681                 let mut sle = SpanlessEq::new(cx).deny_side_effects();
 682                 match &*ps.ident.as_str() {
 683                     "span_suggestion" if sle.eq_expr(&and_then_args[2], &span_call_args[1]) => {
 684                         suggest_suggestion(cx, expr, &and_then_snippets, &span_suggestion_snippets(cx, span_call_args));
 685                     },
 686                     "span_help" if sle.eq_expr(&and_then_args[2], &span_call_args[1]) => {
 687                         let help_snippet = snippet(cx, span_call_args[2].span, r#""...""#);
 688                         suggest_help(cx, expr, &and_then_snippets, help_snippet.borrow(), true);
 689                     },
 690                     "span_note" if sle.eq_expr(&and_then_args[2], &span_call_args[1]) => {
 691                         let note_snippet = snippet(cx, span_call_args[2].span, r#""...""#);
 692                         suggest_note(cx, expr, &and_then_snippets, note_snippet.borrow(), true);
 693                     },
 694                     "help" => {
 695                         let help_snippet = snippet(cx, span_call_args[1].span, r#""...""#);
 696                         suggest_help(cx, expr, &and_then_snippets, help_snippet.borrow(), false);
 697                     }
 698                     "note" => {
 699                         let note_snippet = snippet(cx, span_call_args[1].span, r#""...""#);
 700                         suggest_note(cx, expr, &and_then_snippets, note_snippet.borrow(), false);
 701                     }
 702                     _  => (),
 703                 }
 704             }
 705         }
 706     }
 707 }
 708
 709 struct AndThenSnippets<'a> {
 710     cx: Cow<'a, str>,
 711     lint: Cow<'a, str>,
 712     span: Cow<'a, str>,
 713     msg: Cow<'a, str>,
 714 }
 715
 716 fn get_and_then_snippets<'a, 'hir>(cx: &LateContext<'_>, and_then_snippets: &'hir [Expr<'hir>]) -> AndThenSnippets<'a> {
 717     let cx_snippet = snippet(cx, and_then_snippets[0].span, "cx");
 718     let lint_snippet = snippet(cx, and_then_snippets[1].span, "..");
 719     let span_snippet = snippet(cx, and_then_snippets[2].span, "span");
 720     let msg_snippet = snippet(cx, and_then_snippets[3].span, r#""...""#);
 721
 722     AndThenSnippets {
 723         cx: cx_snippet,
 724         lint: lint_snippet,
 725         span: span_snippet,
 726         msg: msg_snippet,
 727     }
 728 }
 729
 730 struct SpanSuggestionSnippets<'a> {
 731     help: Cow<'a, str>,
 732     sugg: Cow<'a, str>,
 733     applicability: Cow<'a, str>,
 734 }
 735
 736 fn span_suggestion_snippets<'a, 'hir>(
 737     cx: &LateContext<'_>,
 738     span_call_args: &'hir [Expr<'hir>],
 739 ) -> SpanSuggestionSnippets<'a> {
 740     let help_snippet = snippet(cx, span_call_args[2].span, r#""...""#);
 741     let sugg_snippet = snippet(cx, span_call_args[3].span, "..");
 742     let applicability_snippet = snippet(cx, span_call_args[4].span, "Applicability::MachineApplicable");
 743
 744     SpanSuggestionSnippets {
 745         help: help_snippet,
 746         sugg: sugg_snippet,
 747         applicability: applicability_snippet,
 748     }
 749 }
 750
 751 fn suggest_suggestion(
 752     cx: &LateContext<'_>,
 753     expr: &Expr<'_>,
 754     and_then_snippets: &AndThenSnippets<'_>,
 755     span_suggestion_snippets: &SpanSuggestionSnippets<'_>,
 756 ) {
 757     span_lint_and_sugg(
 758         cx,
 759         COLLAPSIBLE_SPAN_LINT_CALLS,
 760         expr.span,
 761         "this call is collapsible",
 762         "collapse into",
 763         format!(
 764             "span_lint_and_sugg({}, {}, {}, {}, {}, {}, {})",
 765             and_then_snippets.cx,
 766             and_then_snippets.lint,
 767             and_then_snippets.span,
 768             and_then_snippets.msg,
 769             span_suggestion_snippets.help,
 770             span_suggestion_snippets.sugg,
 771             span_suggestion_snippets.applicability
 772         ),
 773         Applicability::MachineApplicable,
 774     );
 775 }
 776
 777 fn suggest_help(
 778     cx: &LateContext<'_>,
 779     expr: &Expr<'_>,
 780     and_then_snippets: &AndThenSnippets<'_>,
 781     help: &str,
 782     with_span: bool,
 783 ) {
 784     let option_span = if with_span {
 785         format!("Some({})", and_then_snippets.span)
 786     } else {
 787         "None".to_string()
 788     };
 789
 790     span_lint_and_sugg(
 791         cx,
 792         COLLAPSIBLE_SPAN_LINT_CALLS,
 793         expr.span,
 794         "this call is collapsible",
 795         "collapse into",
 796         format!(
 797             "span_lint_and_help({}, {}, {}, {}, {}, {})",
 798             and_then_snippets.cx,
 799             and_then_snippets.lint,
 800             and_then_snippets.span,
 801             and_then_snippets.msg,
 802             &option_span,
 803             help
 804         ),
 805         Applicability::MachineApplicable,
 806     );
 807 }
 808
 809 fn suggest_note(
 810     cx: &LateContext<'_>,
 811     expr: &Expr<'_>,
 812     and_then_snippets: &AndThenSnippets<'_>,
 813     note: &str,
 814     with_span: bool,
 815 ) {
 816     let note_span = if with_span {
 817         format!("Some({})", and_then_snippets.span)
 818     } else {
 819         "None".to_string()
 820     };
 821
 822     span_lint_and_sugg(
 823         cx,
 824         COLLAPSIBLE_SPAN_LINT_CALLS,
 825         expr.span,
 826         "this call is collspible",
 827         "collapse into",
 828         format!(
 829             "span_lint_and_note({}, {}, {}, {}, {}, {})",
 830             and_then_snippets.cx,
 831             and_then_snippets.lint,
 832             and_then_snippets.span,
 833             and_then_snippets.msg,
 834             note_span,
 835             note
 836         ),
 837         Applicability::MachineApplicable,
 838     );
 839 }
 840
 841 declare_lint_pass!(MatchTypeOnDiagItem => [MATCH_TYPE_ON_DIAGNOSTIC_ITEM]);
 842
 843 impl<'tcx> LateLintPass<'tcx> for MatchTypeOnDiagItem {
 844     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
 845         if is_lint_allowed(cx, MATCH_TYPE_ON_DIAGNOSTIC_ITEM, expr.hir_id) {
 846             return;
 847         }
 848
 849         if_chain! {
 850             // Check if this is a call to utils::match_type()
 851             if let ExprKind::Call(fn_path, [context, ty, ty_path]) = expr.kind;
 852             if is_expr_path_def_path(cx, fn_path, &["clippy_utils", "ty", "match_type"]);
 853             // Extract the path to the matched type
 854             if let Some(segments) = path_to_matched_type(cx, ty_path);
 855             let segments: Vec<&str> = segments.iter().map(Symbol::as_str).collect();
 856             if let Some(ty_did) = def_path_res(cx, &segments[..]).opt_def_id();
 857             // Check if the matched type is a diagnostic item
 858             if let Some(item_name) = cx.tcx.get_diagnostic_name(ty_did);
 859             then {
 860                 // TODO: check paths constants from external crates.
 861                 let cx_snippet = snippet(cx, context.span, "_");
 862                 let ty_snippet = snippet(cx, ty.span, "_");
 863
 864                 span_lint_and_sugg(
 865                     cx,
 866                     MATCH_TYPE_ON_DIAGNOSTIC_ITEM,
 867                     expr.span,
 868                     "usage of `clippy_utils::ty::match_type()` on a type diagnostic item",
 869                     "try",
 870                     format!("clippy_utils::ty::is_type_diagnostic_item({}, {}, sym::{})", cx_snippet, ty_snippet, item_name),
 871                     Applicability::MaybeIncorrect,
 872                 );
 873             }
 874         }
 875     }
 876 }
 877
 878 fn path_to_matched_type(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<Vec<Symbol>> {
 879     use rustc_hir::ItemKind;
 880
 881     match &expr.kind {
 882         ExprKind::AddrOf(.., expr) => return path_to_matched_type(cx, expr),
 883         ExprKind::Path(qpath) => match cx.qpath_res(qpath, expr.hir_id) {
 884             Res::Local(hir_id) => {
 885                 let parent_id = cx.tcx.hir().get_parent_node(hir_id);
 886                 if let Some(Node::Local(local)) = cx.tcx.hir().find(parent_id) {
 887                     if let Some(init) = local.init {
 888                         return path_to_matched_type(cx, init);
 889                     }
 890                 }
 891             },
 892             Res::Def(DefKind::Const | DefKind::Static(..), def_id) => {
 893                 if let Some(Node::Item(item)) = cx.tcx.hir().get_if_local(def_id) {
 894                     if let ItemKind::Const(.., body_id) | ItemKind::Static(.., body_id) = item.kind {
 895                         let body = cx.tcx.hir().body(body_id);
 896                         return path_to_matched_type(cx, &body.value);
 897                     }
 898                 }
 899             },
 900             _ => {},
 901         },
 902         ExprKind::Array(exprs) => {
 903             let segments: Vec<Symbol> = exprs
 904                 .iter()
 905                 .filter_map(|expr| {
 906                     if let ExprKind::Lit(lit) = &expr.kind {
 907                         if let LitKind::Str(sym, _) = lit.node {
 908                             return Some(sym);
 909                         }
 910                     }
 911
 912                     None
 913                 })
 914                 .collect();
 915
 916             if segments.len() == exprs.len() {
 917                 return Some(segments);
 918             }
 919         },
 920         _ => {},
 921     }
 922
 923     None
 924 }
 925
 926 // This is not a complete resolver for paths. It works on all the paths currently used in the paths
 927 // module.  That's all it does and all it needs to do.
 928 pub fn check_path(cx: &LateContext<'_>, path: &[&str]) -> bool {
 929     if def_path_res(cx, path) != Res::Err {
 930         return true;
 931     }
 932
 933     // Some implementations can't be found by `path_to_res`, particularly inherent
 934     // implementations of native types. Check lang items.
 935     let path_syms: Vec<_> = path.iter().map(|p| Symbol::intern(p)).collect();
 936     let lang_items = cx.tcx.lang_items();
 937     // This list isn't complete, but good enough for our current list of paths.
 938     let incoherent_impls = [
 939         SimplifiedTypeGen::FloatSimplifiedType(FloatTy::F32),
 940         SimplifiedTypeGen::FloatSimplifiedType(FloatTy::F64),
 941         SimplifiedTypeGen::SliceSimplifiedType,
 942         SimplifiedTypeGen::StrSimplifiedType,
 943     ]
 944     .iter()
 945     .flat_map(|&ty| cx.tcx.incoherent_impls(ty));
 946     for item_def_id in lang_items.items().iter().flatten().chain(incoherent_impls) {
 947         let lang_item_path = cx.get_def_path(*item_def_id);
 948         if path_syms.starts_with(&lang_item_path) {
 949             if let [item] = &path_syms[lang_item_path.len()..] {
 950                 if matches!(
 951                     cx.tcx.def_kind(*item_def_id),
 952                     DefKind::Mod | DefKind::Enum | DefKind::Trait
 953                 ) {
 954                     for child in cx.tcx.module_children(*item_def_id) {
 955                         if child.ident.name == *item {
 956                             return true;
 957                         }
 958                     }
 959                 } else {
 960                     for child in cx.tcx.associated_item_def_ids(*item_def_id) {
 961                         if cx.tcx.item_name(*child) == *item {
 962                             return true;
 963                         }
 964                     }
 965                 }
 966             }
 967         }
 968     }
 969
 970     false
 971 }
 972
 973 declare_lint_pass!(InvalidPaths => [INVALID_PATHS]);
 974
 975 impl<'tcx> LateLintPass<'tcx> for InvalidPaths {
 976     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 977         let local_def_id = &cx.tcx.parent_module(item.hir_id());
 978         let mod_name = &cx.tcx.item_name(local_def_id.to_def_id());
 979         if_chain! {
 980             if mod_name.as_str() == "paths";
 981             if let hir::ItemKind::Const(ty, body_id) = item.kind;
 982             let ty = hir_ty_to_ty(cx.tcx, ty);
 983             if let ty::Array(el_ty, _) = &ty.kind();
 984             if let ty::Ref(_, el_ty, _) = &el_ty.kind();
 985             if el_ty.is_str();
 986             let body = cx.tcx.hir().body(body_id);
 987             let typeck_results = cx.tcx.typeck_body(body_id);
 988             if let Some(Constant::Vec(path)) = constant_simple(cx, typeck_results, &body.value);
 989             let path: Vec<&str> = path.iter().map(|x| {
 990                     if let Constant::Str(s) = x {
 991                         s.as_str()
 992                     } else {
 993                         // We checked the type of the constant above
 994                         unreachable!()
 995                     }
 996                 }).collect();
 997             if !check_path(cx, &path[..]);
 998             then {
 999                 span_lint(cx, INVALID_PATHS, item.span, "invalid path");
1000             }
1001         }
1002     }
1003 }
1004
1005 #[derive(Default)]
1006 pub struct InterningDefinedSymbol {
1007     // Maps the symbol value to the constant DefId.
1008     symbol_map: FxHashMap<u32, DefId>,
1009 }
1010
1011 impl_lint_pass!(InterningDefinedSymbol => [INTERNING_DEFINED_SYMBOL, UNNECESSARY_SYMBOL_STR]);
1012
1013 impl<'tcx> LateLintPass<'tcx> for InterningDefinedSymbol {
1014     fn check_crate(&mut self, cx: &LateContext<'_>) {
1015         if !self.symbol_map.is_empty() {
1016             return;
1017         }
1018
1019         for &module in &[&paths::KW_MODULE, &paths::SYM_MODULE] {
1020             if let Some(def_id) = def_path_res(cx, module).opt_def_id() {
1021                 for item in cx.tcx.module_children(def_id).iter() {
1022                     if_chain! {
1023                         if let Res::Def(DefKind::Const, item_def_id) = item.res;
1024                         let ty = cx.tcx.type_of(item_def_id);
1025                         if match_type(cx, ty, &paths::SYMBOL);
1026                         if let Ok(ConstValue::Scalar(value)) = cx.tcx.const_eval_poly(item_def_id);
1027                         if let Ok(value) = value.to_u32();
1028                         then {
1029                             self.symbol_map.insert(value, item_def_id);
1030                         }
1031                     }
1032                 }
1033             }
1034         }
1035     }
1036
1037     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1038         if_chain! {
1039             if let ExprKind::Call(func, [arg]) = &expr.kind;
1040             if let ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(func).kind();
1041             if match_def_path(cx, *def_id, &paths::SYMBOL_INTERN);
1042             if let Some(Constant::Str(arg)) = constant_simple(cx, cx.typeck_results(), arg);
1043             let value = Symbol::intern(&arg).as_u32();
1044             if let Some(&def_id) = self.symbol_map.get(&value);
1045             then {
1046                 span_lint_and_sugg(
1047                     cx,
1048                     INTERNING_DEFINED_SYMBOL,
1049                     is_expn_of(expr.span, "sym").unwrap_or(expr.span),
1050                     "interning a defined symbol",
1051                     "try",
1052                     cx.tcx.def_path_str(def_id),
1053                     Applicability::MachineApplicable,
1054                 );
1055             }
1056         }
1057         if let ExprKind::Binary(op, left, right) = expr.kind {
1058             if matches!(op.node, BinOpKind::Eq | BinOpKind::Ne) {
1059                 let data = [
1060                     (left, self.symbol_str_expr(left, cx)),
1061                     (right, self.symbol_str_expr(right, cx)),
1062                 ];
1063                 match data {
1064                     // both operands are a symbol string
1065                     [(_, Some(left)), (_, Some(right))] => {
1066                         span_lint_and_sugg(
1067                             cx,
1068                             UNNECESSARY_SYMBOL_STR,
1069                             expr.span,
1070                             "unnecessary `Symbol` to string conversion",
1071                             "try",
1072                             format!(
1073                                 "{} {} {}",
1074                                 left.as_symbol_snippet(cx),
1075                                 op.node.as_str(),
1076                                 right.as_symbol_snippet(cx),
1077                             ),
1078                             Applicability::MachineApplicable,
1079                         );
1080                     },
1081                     // one of the operands is a symbol string
1082                     [(expr, Some(symbol)), _] | [_, (expr, Some(symbol))] => {
1083                         // creating an owned string for comparison
1084                         if matches!(symbol, SymbolStrExpr::Expr { is_to_owned: true, .. }) {
1085                             span_lint_and_sugg(
1086                                 cx,
1087                                 UNNECESSARY_SYMBOL_STR,
1088                                 expr.span,
1089                                 "unnecessary string allocation",
1090                                 "try",
1091                                 format!("{}.as_str()", symbol.as_symbol_snippet(cx)),
1092                                 Applicability::MachineApplicable,
1093                             );
1094                         }
1095                     },
1096                     // nothing found
1097                     [(_, None), (_, None)] => {},
1098                 }
1099             }
1100         }
1101     }
1102 }
1103
1104 impl InterningDefinedSymbol {
1105     fn symbol_str_expr<'tcx>(&self, expr: &'tcx Expr<'tcx>, cx: &LateContext<'tcx>) -> Option<SymbolStrExpr<'tcx>> {
1106         static IDENT_STR_PATHS: &[&[&str]] = &[&paths::IDENT_AS_STR, &paths::TO_STRING_METHOD];
1107         static SYMBOL_STR_PATHS: &[&[&str]] = &[
1108             &paths::SYMBOL_AS_STR,
1109             &paths::SYMBOL_TO_IDENT_STRING,
1110             &paths::TO_STRING_METHOD,
1111         ];
1112         let call = if_chain! {
1113             if let ExprKind::AddrOf(_, _, e) = expr.kind;
1114             if let ExprKind::Unary(UnOp::Deref, e) = e.kind;
1115             then { e } else { expr }
1116         };
1117         if_chain! {
1118             // is a method call
1119             if let ExprKind::MethodCall(_, [item], _) = call.kind;
1120             if let Some(did) = cx.typeck_results().type_dependent_def_id(call.hir_id);
1121             let ty = cx.typeck_results().expr_ty(item);
1122             // ...on either an Ident or a Symbol
1123             if let Some(is_ident) = if match_type(cx, ty, &paths::SYMBOL) {
1124                 Some(false)
1125             } else if match_type(cx, ty, &paths::IDENT) {
1126                 Some(true)
1127             } else {
1128                 None
1129             };
1130             // ...which converts it to a string
1131             let paths = if is_ident { IDENT_STR_PATHS } else { SYMBOL_STR_PATHS };
1132             if let Some(path) = paths.iter().find(|path| match_def_path(cx, did, path));
1133             then {
1134                 let is_to_owned = path.last().unwrap().ends_with("string");
1135                 return Some(SymbolStrExpr::Expr {
1136                     item,
1137                     is_ident,
1138                     is_to_owned,
1139                 });
1140             }
1141         }
1142         // is a string constant
1143         if let Some(Constant::Str(s)) = constant_simple(cx, cx.typeck_results(), expr) {
1144             let value = Symbol::intern(&s).as_u32();
1145             // ...which matches a symbol constant
1146             if let Some(&def_id) = self.symbol_map.get(&value) {
1147                 return Some(SymbolStrExpr::Const(def_id));
1148             }
1149         }
1150         None
1151     }
1152 }
1153
1154 enum SymbolStrExpr<'tcx> {
1155     /// a string constant with a corresponding symbol constant
1156     Const(DefId),
1157     /// a "symbol to string" expression like `symbol.as_str()`
1158     Expr {
1159         /// part that evaluates to `Symbol` or `Ident`
1160         item: &'tcx Expr<'tcx>,
1161         is_ident: bool,
1162         /// whether an owned `String` is created like `to_ident_string()`
1163         is_to_owned: bool,
1164     },
1165 }
1166
1167 impl<'tcx> SymbolStrExpr<'tcx> {
1168     /// Returns a snippet that evaluates to a `Symbol` and is const if possible
1169     fn as_symbol_snippet(&self, cx: &LateContext<'_>) -> Cow<'tcx, str> {
1170         match *self {
1171             Self::Const(def_id) => cx.tcx.def_path_str(def_id).into(),
1172             Self::Expr { item, is_ident, .. } => {
1173                 let mut snip = snippet(cx, item.span.source_callsite(), "..");
1174                 if is_ident {
1175                     // get `Ident.name`
1176                     snip.to_mut().push_str(".name");
1177                 }
1178                 snip
1179             },
1180         }
1181     }
1182 }
1183
1184 declare_lint_pass!(IfChainStyle => [IF_CHAIN_STYLE]);
1185
1186 impl<'tcx> LateLintPass<'tcx> for IfChainStyle {
1187     fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
1188         let (local, after, if_chain_span) = if_chain! {
1189             if let [Stmt { kind: StmtKind::Local(local), .. }, after @ ..] = block.stmts;
1190             if let Some(if_chain_span) = is_expn_of(block.span, "if_chain");
1191             then { (local, after, if_chain_span) } else { return }
1192         };
1193         if is_first_if_chain_expr(cx, block.hir_id, if_chain_span) {
1194             span_lint(
1195                 cx,
1196                 IF_CHAIN_STYLE,
1197                 if_chain_local_span(cx, local, if_chain_span),
1198                 "`let` expression should be above the `if_chain!`",
1199             );
1200         } else if local.span.ctxt() == block.span.ctxt() && is_if_chain_then(after, block.expr, if_chain_span) {
1201             span_lint(
1202                 cx,
1203                 IF_CHAIN_STYLE,
1204                 if_chain_local_span(cx, local, if_chain_span),
1205                 "`let` expression should be inside `then { .. }`",
1206             );
1207         }
1208     }
1209
1210     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
1211         let (cond, then, els) = if let Some(higher::IfOrIfLet { cond, r#else, then }) = higher::IfOrIfLet::hir(expr) {
1212             (cond, then, r#else.is_some())
1213         } else {
1214             return;
1215         };
1216         let then_block = match then.kind {
1217             ExprKind::Block(block, _) => block,
1218             _ => return,
1219         };
1220         let if_chain_span = is_expn_of(expr.span, "if_chain");
1221         if !els {
1222             check_nested_if_chains(cx, expr, then_block, if_chain_span);
1223         }
1224         let if_chain_span = match if_chain_span {
1225             None => return,
1226             Some(span) => span,
1227         };
1228         // check for `if a && b;`
1229         if_chain! {
1230             if let ExprKind::Binary(op, _, _) = cond.kind;
1231             if op.node == BinOpKind::And;
1232             if cx.sess().source_map().is_multiline(cond.span);
1233             then {
1234                 span_lint(cx, IF_CHAIN_STYLE, cond.span, "`if a && b;` should be `if a; if b;`");
1235             }
1236         }
1237         if is_first_if_chain_expr(cx, expr.hir_id, if_chain_span)
1238             && is_if_chain_then(then_block.stmts, then_block.expr, if_chain_span)
1239         {
1240             span_lint(cx, IF_CHAIN_STYLE, expr.span, "`if_chain!` only has one `if`");
1241         }
1242     }
1243 }
1244
1245 fn check_nested_if_chains(
1246     cx: &LateContext<'_>,
1247     if_expr: &Expr<'_>,
1248     then_block: &Block<'_>,
1249     if_chain_span: Option<Span>,
1250 ) {
1251     #[rustfmt::skip]
1252     let (head, tail) = match *then_block {
1253         Block { stmts, expr: Some(tail), .. } => (stmts, tail),
1254         Block {
1255             stmts: &[
1256                 ref head @ ..,
1257                 Stmt { kind: StmtKind::Expr(tail) | StmtKind::Semi(tail), .. }
1258             ],
1259             ..
1260         } => (head, tail),
1261         _ => return,
1262     };
1263     if_chain! {
1264         if let Some(higher::IfOrIfLet { r#else: None, .. }) = higher::IfOrIfLet::hir(tail);
1265         let sm = cx.sess().source_map();
1266         if head
1267             .iter()
1268             .all(|stmt| matches!(stmt.kind, StmtKind::Local(..)) && !sm.is_multiline(stmt.span));
1269         if if_chain_span.is_some() || !is_else_clause(cx.tcx, if_expr);
1270         then {} else { return }
1271     }
1272     let (span, msg) = match (if_chain_span, is_expn_of(tail.span, "if_chain")) {
1273         (None, Some(_)) => (if_expr.span, "this `if` can be part of the inner `if_chain!`"),
1274         (Some(_), None) => (tail.span, "this `if` can be part of the outer `if_chain!`"),
1275         (Some(a), Some(b)) if a != b => (b, "this `if_chain!` can be merged with the outer `if_chain!`"),
1276         _ => return,
1277     };
1278     span_lint_and_then(cx, IF_CHAIN_STYLE, span, msg, |diag| {
1279         let (span, msg) = match head {
1280             [] => return,
1281             [stmt] => (stmt.span, "this `let` statement can also be in the `if_chain!`"),
1282             [a, .., b] => (
1283                 a.span.to(b.span),
1284                 "these `let` statements can also be in the `if_chain!`",
1285             ),
1286         };
1287         diag.span_help(span, msg);
1288     });
1289 }
1290
1291 fn is_first_if_chain_expr(cx: &LateContext<'_>, hir_id: HirId, if_chain_span: Span) -> bool {
1292     cx.tcx
1293         .hir()
1294         .parent_iter(hir_id)
1295         .find(|(_, node)| {
1296             #[rustfmt::skip]
1297             !matches!(node, Node::Expr(Expr { kind: ExprKind::Block(..), .. }) | Node::Stmt(_))
1298         })
1299         .map_or(false, |(id, _)| {
1300             is_expn_of(cx.tcx.hir().span(id), "if_chain") != Some(if_chain_span)
1301         })
1302 }
1303
1304 /// Checks a trailing slice of statements and expression of a `Block` to see if they are part
1305 /// of the `then {..}` portion of an `if_chain!`
1306 fn is_if_chain_then(stmts: &[Stmt<'_>], expr: Option<&Expr<'_>>, if_chain_span: Span) -> bool {
1307     let span = if let [stmt, ..] = stmts {
1308         stmt.span
1309     } else if let Some(expr) = expr {
1310         expr.span
1311     } else {
1312         // empty `then {}`
1313         return true;
1314     };
1315     is_expn_of(span, "if_chain").map_or(true, |span| span != if_chain_span)
1316 }
1317
1318 /// Creates a `Span` for `let x = ..;` in an `if_chain!` call.
1319 fn if_chain_local_span(cx: &LateContext<'_>, local: &Local<'_>, if_chain_span: Span) -> Span {
1320     let mut span = local.pat.span;
1321     if let Some(init) = local.init {
1322         span = span.to(init.span);
1323     }
1324     span.adjust(if_chain_span.ctxt().outer_expn());
1325     let sm = cx.sess().source_map();
1326     let span = sm.span_extend_to_prev_str(span, "let", false, true).unwrap_or(span);
1327     let span = sm.span_extend_to_next_char(span, ';', false);
1328     Span::new(
1329         span.lo() - BytePos(3),
1330         span.hi() + BytePos(1),
1331         span.ctxt(),
1332         span.parent(),
1333     )
1334 }
1335
1336 declare_lint_pass!(MsrvAttrImpl => [MISSING_MSRV_ATTR_IMPL]);
1337
1338 impl LateLintPass<'_> for MsrvAttrImpl {
1339     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
1340         if_chain! {
1341             if let hir::ItemKind::Impl(hir::Impl {
1342                 of_trait: Some(lint_pass_trait_ref),
1343                 self_ty,
1344                 items,
1345                 ..
1346             }) = &item.kind;
1347             if let Some(lint_pass_trait_def_id) = lint_pass_trait_ref.trait_def_id();
1348             let is_late_pass = match_def_path(cx, lint_pass_trait_def_id, &paths::LATE_LINT_PASS);
1349             if is_late_pass || match_def_path(cx, lint_pass_trait_def_id, &paths::EARLY_LINT_PASS);
1350             let self_ty = hir_ty_to_ty(cx.tcx, self_ty);
1351             if let ty::Adt(self_ty_def, _) = self_ty.kind();
1352             if self_ty_def.is_struct();
1353             if self_ty_def.all_fields().any(|f| {
1354                 cx.tcx
1355                     .type_of(f.did)
1356                     .walk()
1357                     .filter(|t| matches!(t.unpack(), GenericArgKind::Type(_)))
1358                     .any(|t| match_type(cx, t.expect_ty(), &paths::RUSTC_VERSION))
1359             });
1360             if !items.iter().any(|item| item.ident.name == sym!(enter_lint_attrs));
1361             then {
1362                 let context = if is_late_pass { "LateContext" } else { "EarlyContext" };
1363                 let lint_pass = if is_late_pass { "LateLintPass" } else { "EarlyLintPass" };
1364                 let span = cx.sess().source_map().span_through_char(item.span, '{');
1365                 span_lint_and_sugg(
1366                     cx,
1367                     MISSING_MSRV_ATTR_IMPL,
1368                     span,
1369                     &format!("`extract_msrv_attr!` macro missing from `{lint_pass}` implementation"),
1370                     &format!("add `extract_msrv_attr!({context})` to the `{lint_pass}` implementation"),
1371                     format!("{}\n    extract_msrv_attr!({context});", snippet(cx, span, "..")),
1372                     Applicability::MachineApplicable,
1373                 );
1374             }
1375         }
1376     }
1377 }