src/tools/clippy/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;
  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_lint_pass!(ClippyLintsInternal => [CLIPPY_LINTS_INTERNAL]);
 341
 342 impl EarlyLintPass for ClippyLintsInternal {
 343     fn check_crate(&mut self, cx: &EarlyContext<'_>, krate: &Crate) {
 344         if let Some(utils) = krate.items.iter().find(|item| item.ident.name.as_str() == "utils") {
 345             if let ItemKind::Mod(_, ModKind::Loaded(ref items, ..)) = utils.kind {
 346                 if let Some(paths) = items.iter().find(|item| item.ident.name.as_str() == "paths") {
 347                     if let ItemKind::Mod(_, ModKind::Loaded(ref items, ..)) = paths.kind {
 348                         let mut last_name: Option<&str> = None;
 349                         for item in items {
 350                             let name = item.ident.as_str();
 351                             if let Some(last_name) = last_name {
 352                                 if *last_name > *name {
 353                                     span_lint(
 354                                         cx,
 355                                         CLIPPY_LINTS_INTERNAL,
 356                                         item.span,
 357                                         "this constant should be before the previous constant due to lexical \
 358                                          ordering",
 359                                     );
 360                                 }
 361                             }
 362                             last_name = Some(name);
 363                         }
 364                     }
 365                 }
 366             }
 367         }
 368     }
 369 }
 370
 371 #[derive(Clone, Debug, Default)]
 372 pub struct LintWithoutLintPass {
 373     declared_lints: FxHashMap<Symbol, Span>,
 374     registered_lints: FxHashSet<Symbol>,
 375 }
 376
 377 impl_lint_pass!(LintWithoutLintPass => [DEFAULT_LINT, LINT_WITHOUT_LINT_PASS, INVALID_CLIPPY_VERSION_ATTRIBUTE, MISSING_CLIPPY_VERSION_ATTRIBUTE]);
 378
 379 impl<'tcx> LateLintPass<'tcx> for LintWithoutLintPass {
 380     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 381         if is_lint_allowed(cx, DEFAULT_LINT, item.hir_id()) {
 382             return;
 383         }
 384
 385         if let hir::ItemKind::Static(ty, Mutability::Not, body_id) = item.kind {
 386             if is_lint_ref_type(cx, ty) {
 387                 check_invalid_clippy_version_attribute(cx, item);
 388
 389                 let expr = &cx.tcx.hir().body(body_id).value;
 390                 if_chain! {
 391                     if let ExprKind::AddrOf(_, _, inner_exp) = expr.kind;
 392                     if let ExprKind::Struct(_, fields, _) = inner_exp.kind;
 393                     let field = fields
 394                         .iter()
 395                         .find(|f| f.ident.as_str() == "desc")
 396                         .expect("lints must have a description field");
 397                     if let ExprKind::Lit(Spanned {
 398                         node: LitKind::Str(ref sym, _),
 399                         ..
 400                     }) = field.expr.kind;
 401                     if sym.as_str() == "default lint description";
 402
 403                     then {
 404                         span_lint(
 405                             cx,
 406                             DEFAULT_LINT,
 407                             item.span,
 408                             &format!("the lint `{}` has the default lint description", item.ident.name),
 409                         );
 410                     }
 411                 }
 412                 self.declared_lints.insert(item.ident.name, item.span);
 413             }
 414         } else if let Some(macro_call) = root_macro_call_first_node(cx, item) {
 415             if !matches!(
 416                 &*cx.tcx.item_name(macro_call.def_id).as_str(),
 417                 "impl_lint_pass" | "declare_lint_pass"
 418             ) {
 419                 return;
 420             }
 421             if let hir::ItemKind::Impl(hir::Impl {
 422                 of_trait: None,
 423                 items: impl_item_refs,
 424                 ..
 425             }) = item.kind
 426             {
 427                 let mut collector = LintCollector {
 428                     output: &mut self.registered_lints,
 429                     cx,
 430                 };
 431                 let body_id = cx.tcx.hir().body_owned_by(
 432                     impl_item_refs
 433                         .iter()
 434                         .find(|iiref| iiref.ident.as_str() == "get_lints")
 435                         .expect("LintPass needs to implement get_lints")
 436                         .id
 437                         .hir_id(),
 438                 );
 439                 collector.visit_expr(&cx.tcx.hir().body(body_id).value);
 440             }
 441         }
 442     }
 443
 444     fn check_crate_post(&mut self, cx: &LateContext<'tcx>) {
 445         if is_lint_allowed(cx, LINT_WITHOUT_LINT_PASS, CRATE_HIR_ID) {
 446             return;
 447         }
 448
 449         for (lint_name, &lint_span) in &self.declared_lints {
 450             // When using the `declare_tool_lint!` macro, the original `lint_span`'s
 451             // file points to "<rustc macros>".
 452             // `compiletest-rs` thinks that's an error in a different file and
 453             // just ignores it. This causes the test in compile-fail/lint_pass
 454             // not able to capture the error.
 455             // Therefore, we need to climb the macro expansion tree and find the
 456             // actual span that invoked `declare_tool_lint!`:
 457             let lint_span = lint_span.ctxt().outer_expn_data().call_site;
 458
 459             if !self.registered_lints.contains(lint_name) {
 460                 span_lint(
 461                     cx,
 462                     LINT_WITHOUT_LINT_PASS,
 463                     lint_span,
 464                     &format!("the lint `{}` is not added to any `LintPass`", lint_name),
 465                 );
 466             }
 467         }
 468     }
 469 }
 470
 471 fn is_lint_ref_type<'tcx>(cx: &LateContext<'tcx>, ty: &Ty<'_>) -> bool {
 472     if let TyKind::Rptr(
 473         _,
 474         MutTy {
 475             ty: inner,
 476             mutbl: Mutability::Not,
 477         },
 478     ) = ty.kind
 479     {
 480         if let TyKind::Path(ref path) = inner.kind {
 481             if let Res::Def(DefKind::Struct, def_id) = cx.qpath_res(path, inner.hir_id) {
 482                 return match_def_path(cx, def_id, &paths::LINT);
 483             }
 484         }
 485     }
 486
 487     false
 488 }
 489
 490 fn check_invalid_clippy_version_attribute(cx: &LateContext<'_>, item: &'_ Item<'_>) {
 491     if let Some(value) = extract_clippy_version_value(cx, item) {
 492         // The `sym!` macro doesn't work as it only expects a single token.
 493         // It's better to keep it this way and have a direct `Symbol::intern` call here.
 494         if value == Symbol::intern("pre 1.29.0") {
 495             return;
 496         }
 497
 498         if RustcVersion::parse(&*value.as_str()).is_err() {
 499             span_lint_and_help(
 500                 cx,
 501                 INVALID_CLIPPY_VERSION_ATTRIBUTE,
 502                 item.span,
 503                 "this item has an invalid `clippy::version` attribute",
 504                 None,
 505                 "please use a valid sematic version, see `doc/adding_lints.md`",
 506             );
 507         }
 508     } else {
 509         span_lint_and_help(
 510             cx,
 511             MISSING_CLIPPY_VERSION_ATTRIBUTE,
 512             item.span,
 513             "this lint is missing the `clippy::version` attribute or version value",
 514             None,
 515             "please use a `clippy::version` attribute, see `doc/adding_lints.md`",
 516         );
 517     }
 518 }
 519
 520 /// This function extracts the version value of a `clippy::version` attribute if the given value has
 521 /// one
 522 fn extract_clippy_version_value(cx: &LateContext<'_>, item: &'_ Item<'_>) -> Option<Symbol> {
 523     let attrs = cx.tcx.hir().attrs(item.hir_id());
 524     attrs.iter().find_map(|attr| {
 525         if_chain! {
 526             // Identify attribute
 527             if let ast::AttrKind::Normal(ref attr_kind, _) = &attr.kind;
 528             if let [tool_name, attr_name] = &attr_kind.path.segments[..];
 529             if tool_name.ident.name == sym::clippy;
 530             if attr_name.ident.name == sym::version;
 531             if let Some(version) = attr.value_str();
 532             then {
 533                 Some(version)
 534             } else {
 535                 None
 536             }
 537         }
 538     })
 539 }
 540
 541 struct LintCollector<'a, 'tcx> {
 542     output: &'a mut FxHashSet<Symbol>,
 543     cx: &'a LateContext<'tcx>,
 544 }
 545
 546 impl<'a, 'tcx> Visitor<'tcx> for LintCollector<'a, 'tcx> {
 547     type NestedFilter = nested_filter::All;
 548
 549     fn visit_path(&mut self, path: &'tcx Path<'_>, _: HirId) {
 550         if path.segments.len() == 1 {
 551             self.output.insert(path.segments[0].ident.name);
 552         }
 553     }
 554
 555     fn nested_visit_map(&mut self) -> Self::Map {
 556         self.cx.tcx.hir()
 557     }
 558 }
 559
 560 #[derive(Clone, Default)]
 561 pub struct CompilerLintFunctions {
 562     map: FxHashMap<&'static str, &'static str>,
 563 }
 564
 565 impl CompilerLintFunctions {
 566     #[must_use]
 567     pub fn new() -> Self {
 568         let mut map = FxHashMap::default();
 569         map.insert("span_lint", "utils::span_lint");
 570         map.insert("struct_span_lint", "utils::span_lint");
 571         map.insert("lint", "utils::span_lint");
 572         map.insert("span_lint_note", "utils::span_lint_and_note");
 573         map.insert("span_lint_help", "utils::span_lint_and_help");
 574         Self { map }
 575     }
 576 }
 577
 578 impl_lint_pass!(CompilerLintFunctions => [COMPILER_LINT_FUNCTIONS]);
 579
 580 impl<'tcx> LateLintPass<'tcx> for CompilerLintFunctions {
 581     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 582         if is_lint_allowed(cx, COMPILER_LINT_FUNCTIONS, expr.hir_id) {
 583             return;
 584         }
 585
 586         if_chain! {
 587             if let ExprKind::MethodCall(path, [self_arg, ..], _) = &expr.kind;
 588             let fn_name = path.ident;
 589             if let Some(sugg) = self.map.get(&*fn_name.as_str());
 590             let ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
 591             if match_type(cx, ty, &paths::EARLY_CONTEXT)
 592                 || match_type(cx, ty, &paths::LATE_CONTEXT);
 593             then {
 594                 span_lint_and_help(
 595                     cx,
 596                     COMPILER_LINT_FUNCTIONS,
 597                     path.ident.span,
 598                     "usage of a compiler lint function",
 599                     None,
 600                     &format!("please use the Clippy variant of this function: `{}`", sugg),
 601                 );
 602             }
 603         }
 604     }
 605 }
 606
 607 declare_lint_pass!(OuterExpnDataPass => [OUTER_EXPN_EXPN_DATA]);
 608
 609 impl<'tcx> LateLintPass<'tcx> for OuterExpnDataPass {
 610     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
 611         if is_lint_allowed(cx, OUTER_EXPN_EXPN_DATA, expr.hir_id) {
 612             return;
 613         }
 614
 615         let (method_names, arg_lists, spans) = method_calls(expr, 2);
 616         let method_names: Vec<&str> = method_names.iter().map(Symbol::as_str).collect();
 617         if_chain! {
 618             if let ["expn_data", "outer_expn"] = method_names.as_slice();
 619             let args = arg_lists[1];
 620             if args.len() == 1;
 621             let self_arg = &args[0];
 622             let self_ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
 623             if match_type(cx, self_ty, &paths::SYNTAX_CONTEXT);
 624             then {
 625                 span_lint_and_sugg(
 626                     cx,
 627                     OUTER_EXPN_EXPN_DATA,
 628                     spans[1].with_hi(expr.span.hi()),
 629                     "usage of `outer_expn().expn_data()`",
 630                     "try",
 631                     "outer_expn_data()".to_string(),
 632                     Applicability::MachineApplicable,
 633                 );
 634             }
 635         }
 636     }
 637 }
 638
 639 declare_lint_pass!(ProduceIce => [PRODUCE_ICE]);
 640
 641 impl EarlyLintPass for ProduceIce {
 642     fn check_fn(&mut self, _: &EarlyContext<'_>, fn_kind: FnKind<'_>, _: Span, _: NodeId) {
 643         assert!(!is_trigger_fn(fn_kind), "Would you like some help with that?");
 644     }
 645 }
 646
 647 fn is_trigger_fn(fn_kind: FnKind<'_>) -> bool {
 648     match fn_kind {
 649         FnKind::Fn(_, ident, ..) => ident.name.as_str() == "it_looks_like_you_are_trying_to_kill_clippy",
 650         FnKind::Closure(..) => false,
 651     }
 652 }
 653
 654 declare_lint_pass!(CollapsibleCalls => [COLLAPSIBLE_SPAN_LINT_CALLS]);
 655
 656 impl<'tcx> LateLintPass<'tcx> for CollapsibleCalls {
 657     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
 658         if is_lint_allowed(cx, COLLAPSIBLE_SPAN_LINT_CALLS, expr.hir_id) {
 659             return;
 660         }
 661
 662         if_chain! {
 663             if let ExprKind::Call(func, and_then_args) = expr.kind;
 664             if is_expr_path_def_path(cx, func, &["clippy_utils", "diagnostics", "span_lint_and_then"]);
 665             if and_then_args.len() == 5;
 666             if let ExprKind::Closure(_, _, body_id, _, _) = &and_then_args[4].kind;
 667             let body = cx.tcx.hir().body(*body_id);
 668             let only_expr = peel_blocks_with_stmt(&body.value);
 669             if let ExprKind::MethodCall(ps, span_call_args, _) = &only_expr.kind;
 670             then {
 671                 let and_then_snippets = get_and_then_snippets(cx, and_then_args);
 672                 let mut sle = SpanlessEq::new(cx).deny_side_effects();
 673                 match &*ps.ident.as_str() {
 674                     "span_suggestion" if sle.eq_expr(&and_then_args[2], &span_call_args[1]) => {
 675                         suggest_suggestion(cx, expr, &and_then_snippets, &span_suggestion_snippets(cx, span_call_args));
 676                     },
 677                     "span_help" if sle.eq_expr(&and_then_args[2], &span_call_args[1]) => {
 678                         let help_snippet = snippet(cx, span_call_args[2].span, r#""...""#);
 679                         suggest_help(cx, expr, &and_then_snippets, help_snippet.borrow(), true);
 680                     },
 681                     "span_note" if sle.eq_expr(&and_then_args[2], &span_call_args[1]) => {
 682                         let note_snippet = snippet(cx, span_call_args[2].span, r#""...""#);
 683                         suggest_note(cx, expr, &and_then_snippets, note_snippet.borrow(), true);
 684                     },
 685                     "help" => {
 686                         let help_snippet = snippet(cx, span_call_args[1].span, r#""...""#);
 687                         suggest_help(cx, expr, &and_then_snippets, help_snippet.borrow(), false);
 688                     }
 689                     "note" => {
 690                         let note_snippet = snippet(cx, span_call_args[1].span, r#""...""#);
 691                         suggest_note(cx, expr, &and_then_snippets, note_snippet.borrow(), false);
 692                     }
 693                     _  => (),
 694                 }
 695             }
 696         }
 697     }
 698 }
 699
 700 struct AndThenSnippets<'a> {
 701     cx: Cow<'a, str>,
 702     lint: Cow<'a, str>,
 703     span: Cow<'a, str>,
 704     msg: Cow<'a, str>,
 705 }
 706
 707 fn get_and_then_snippets<'a, 'hir>(cx: &LateContext<'_>, and_then_snippets: &'hir [Expr<'hir>]) -> AndThenSnippets<'a> {
 708     let cx_snippet = snippet(cx, and_then_snippets[0].span, "cx");
 709     let lint_snippet = snippet(cx, and_then_snippets[1].span, "..");
 710     let span_snippet = snippet(cx, and_then_snippets[2].span, "span");
 711     let msg_snippet = snippet(cx, and_then_snippets[3].span, r#""...""#);
 712
 713     AndThenSnippets {
 714         cx: cx_snippet,
 715         lint: lint_snippet,
 716         span: span_snippet,
 717         msg: msg_snippet,
 718     }
 719 }
 720
 721 struct SpanSuggestionSnippets<'a> {
 722     help: Cow<'a, str>,
 723     sugg: Cow<'a, str>,
 724     applicability: Cow<'a, str>,
 725 }
 726
 727 fn span_suggestion_snippets<'a, 'hir>(
 728     cx: &LateContext<'_>,
 729     span_call_args: &'hir [Expr<'hir>],
 730 ) -> SpanSuggestionSnippets<'a> {
 731     let help_snippet = snippet(cx, span_call_args[2].span, r#""...""#);
 732     let sugg_snippet = snippet(cx, span_call_args[3].span, "..");
 733     let applicability_snippet = snippet(cx, span_call_args[4].span, "Applicability::MachineApplicable");
 734
 735     SpanSuggestionSnippets {
 736         help: help_snippet,
 737         sugg: sugg_snippet,
 738         applicability: applicability_snippet,
 739     }
 740 }
 741
 742 fn suggest_suggestion(
 743     cx: &LateContext<'_>,
 744     expr: &Expr<'_>,
 745     and_then_snippets: &AndThenSnippets<'_>,
 746     span_suggestion_snippets: &SpanSuggestionSnippets<'_>,
 747 ) {
 748     span_lint_and_sugg(
 749         cx,
 750         COLLAPSIBLE_SPAN_LINT_CALLS,
 751         expr.span,
 752         "this call is collapsible",
 753         "collapse into",
 754         format!(
 755             "span_lint_and_sugg({}, {}, {}, {}, {}, {}, {})",
 756             and_then_snippets.cx,
 757             and_then_snippets.lint,
 758             and_then_snippets.span,
 759             and_then_snippets.msg,
 760             span_suggestion_snippets.help,
 761             span_suggestion_snippets.sugg,
 762             span_suggestion_snippets.applicability
 763         ),
 764         Applicability::MachineApplicable,
 765     );
 766 }
 767
 768 fn suggest_help(
 769     cx: &LateContext<'_>,
 770     expr: &Expr<'_>,
 771     and_then_snippets: &AndThenSnippets<'_>,
 772     help: &str,
 773     with_span: bool,
 774 ) {
 775     let option_span = if with_span {
 776         format!("Some({})", and_then_snippets.span)
 777     } else {
 778         "None".to_string()
 779     };
 780
 781     span_lint_and_sugg(
 782         cx,
 783         COLLAPSIBLE_SPAN_LINT_CALLS,
 784         expr.span,
 785         "this call is collapsible",
 786         "collapse into",
 787         format!(
 788             "span_lint_and_help({}, {}, {}, {}, {}, {})",
 789             and_then_snippets.cx,
 790             and_then_snippets.lint,
 791             and_then_snippets.span,
 792             and_then_snippets.msg,
 793             &option_span,
 794             help
 795         ),
 796         Applicability::MachineApplicable,
 797     );
 798 }
 799
 800 fn suggest_note(
 801     cx: &LateContext<'_>,
 802     expr: &Expr<'_>,
 803     and_then_snippets: &AndThenSnippets<'_>,
 804     note: &str,
 805     with_span: bool,
 806 ) {
 807     let note_span = if with_span {
 808         format!("Some({})", and_then_snippets.span)
 809     } else {
 810         "None".to_string()
 811     };
 812
 813     span_lint_and_sugg(
 814         cx,
 815         COLLAPSIBLE_SPAN_LINT_CALLS,
 816         expr.span,
 817         "this call is collspible",
 818         "collapse into",
 819         format!(
 820             "span_lint_and_note({}, {}, {}, {}, {}, {})",
 821             and_then_snippets.cx,
 822             and_then_snippets.lint,
 823             and_then_snippets.span,
 824             and_then_snippets.msg,
 825             note_span,
 826             note
 827         ),
 828         Applicability::MachineApplicable,
 829     );
 830 }
 831
 832 declare_lint_pass!(MatchTypeOnDiagItem => [MATCH_TYPE_ON_DIAGNOSTIC_ITEM]);
 833
 834 impl<'tcx> LateLintPass<'tcx> for MatchTypeOnDiagItem {
 835     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
 836         if is_lint_allowed(cx, MATCH_TYPE_ON_DIAGNOSTIC_ITEM, expr.hir_id) {
 837             return;
 838         }
 839
 840         if_chain! {
 841             // Check if this is a call to utils::match_type()
 842             if let ExprKind::Call(fn_path, [context, ty, ty_path]) = expr.kind;
 843             if is_expr_path_def_path(cx, fn_path, &["clippy_utils", "ty", "match_type"]);
 844             // Extract the path to the matched type
 845             if let Some(segments) = path_to_matched_type(cx, ty_path);
 846             let segments: Vec<&str> = segments.iter().map(Symbol::as_str).collect();
 847             if let Some(ty_did) = def_path_res(cx, &segments[..]).opt_def_id();
 848             // Check if the matched type is a diagnostic item
 849             if let Some(item_name) = cx.tcx.get_diagnostic_name(ty_did);
 850             then {
 851                 // TODO: check paths constants from external crates.
 852                 let cx_snippet = snippet(cx, context.span, "_");
 853                 let ty_snippet = snippet(cx, ty.span, "_");
 854
 855                 span_lint_and_sugg(
 856                     cx,
 857                     MATCH_TYPE_ON_DIAGNOSTIC_ITEM,
 858                     expr.span,
 859                     "usage of `clippy_utils::ty::match_type()` on a type diagnostic item",
 860                     "try",
 861                     format!("clippy_utils::ty::is_type_diagnostic_item({}, {}, sym::{})", cx_snippet, ty_snippet, item_name),
 862                     Applicability::MaybeIncorrect,
 863                 );
 864             }
 865         }
 866     }
 867 }
 868
 869 fn path_to_matched_type(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<Vec<Symbol>> {
 870     use rustc_hir::ItemKind;
 871
 872     match &expr.kind {
 873         ExprKind::AddrOf(.., expr) => return path_to_matched_type(cx, expr),
 874         ExprKind::Path(qpath) => match cx.qpath_res(qpath, expr.hir_id) {
 875             Res::Local(hir_id) => {
 876                 let parent_id = cx.tcx.hir().get_parent_node(hir_id);
 877                 if let Some(Node::Local(local)) = cx.tcx.hir().find(parent_id) {
 878                     if let Some(init) = local.init {
 879                         return path_to_matched_type(cx, init);
 880                     }
 881                 }
 882             },
 883             Res::Def(DefKind::Const | DefKind::Static, def_id) => {
 884                 if let Some(Node::Item(item)) = cx.tcx.hir().get_if_local(def_id) {
 885                     if let ItemKind::Const(.., body_id) | ItemKind::Static(.., body_id) = item.kind {
 886                         let body = cx.tcx.hir().body(body_id);
 887                         return path_to_matched_type(cx, &body.value);
 888                     }
 889                 }
 890             },
 891             _ => {},
 892         },
 893         ExprKind::Array(exprs) => {
 894             let segments: Vec<Symbol> = exprs
 895                 .iter()
 896                 .filter_map(|expr| {
 897                     if let ExprKind::Lit(lit) = &expr.kind {
 898                         if let LitKind::Str(sym, _) = lit.node {
 899                             return Some(sym);
 900                         }
 901                     }
 902
 903                     None
 904                 })
 905                 .collect();
 906
 907             if segments.len() == exprs.len() {
 908                 return Some(segments);
 909             }
 910         },
 911         _ => {},
 912     }
 913
 914     None
 915 }
 916
 917 // This is not a complete resolver for paths. It works on all the paths currently used in the paths
 918 // module.  That's all it does and all it needs to do.
 919 pub fn check_path(cx: &LateContext<'_>, path: &[&str]) -> bool {
 920     if def_path_res(cx, path) != Res::Err {
 921         return true;
 922     }
 923
 924     // Some implementations can't be found by `path_to_res`, particularly inherent
 925     // implementations of native types. Check lang items.
 926     let path_syms: Vec<_> = path.iter().map(|p| Symbol::intern(p)).collect();
 927     let lang_items = cx.tcx.lang_items();
 928     for item_def_id in lang_items.items().iter().flatten() {
 929         let lang_item_path = cx.get_def_path(*item_def_id);
 930         if path_syms.starts_with(&lang_item_path) {
 931             if let [item] = &path_syms[lang_item_path.len()..] {
 932                 if matches!(
 933                     cx.tcx.def_kind(*item_def_id),
 934                     DefKind::Mod | DefKind::Enum | DefKind::Trait
 935                 ) {
 936                     for child in cx.tcx.module_children(*item_def_id) {
 937                         if child.ident.name == *item {
 938                             return true;
 939                         }
 940                     }
 941                 } else {
 942                     for child in cx.tcx.associated_item_def_ids(*item_def_id) {
 943                         if cx.tcx.item_name(*child) == *item {
 944                             return true;
 945                         }
 946                     }
 947                 }
 948             }
 949         }
 950     }
 951
 952     false
 953 }
 954
 955 declare_lint_pass!(InvalidPaths => [INVALID_PATHS]);
 956
 957 impl<'tcx> LateLintPass<'tcx> for InvalidPaths {
 958     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 959         let local_def_id = &cx.tcx.parent_module(item.hir_id());
 960         let mod_name = &cx.tcx.item_name(local_def_id.to_def_id());
 961         if_chain! {
 962             if mod_name.as_str() == "paths";
 963             if let hir::ItemKind::Const(ty, body_id) = item.kind;
 964             let ty = hir_ty_to_ty(cx.tcx, ty);
 965             if let ty::Array(el_ty, _) = &ty.kind();
 966             if let ty::Ref(_, el_ty, _) = &el_ty.kind();
 967             if el_ty.is_str();
 968             let body = cx.tcx.hir().body(body_id);
 969             let typeck_results = cx.tcx.typeck_body(body_id);
 970             if let Some(Constant::Vec(path)) = constant_simple(cx, typeck_results, &body.value);
 971             let path: Vec<&str> = path.iter().map(|x| {
 972                     if let Constant::Str(s) = x {
 973                         s.as_str()
 974                     } else {
 975                         // We checked the type of the constant above
 976                         unreachable!()
 977                     }
 978                 }).collect();
 979             if !check_path(cx, &path[..]);
 980             then {
 981                 span_lint(cx, INVALID_PATHS, item.span, "invalid path");
 982             }
 983         }
 984     }
 985 }
 986
 987 #[derive(Default)]
 988 pub struct InterningDefinedSymbol {
 989     // Maps the symbol value to the constant DefId.
 990     symbol_map: FxHashMap<u32, DefId>,
 991 }
 992
 993 impl_lint_pass!(InterningDefinedSymbol => [INTERNING_DEFINED_SYMBOL, UNNECESSARY_SYMBOL_STR]);
 994
 995 impl<'tcx> LateLintPass<'tcx> for InterningDefinedSymbol {
 996     fn check_crate(&mut self, cx: &LateContext<'_>) {
 997         if !self.symbol_map.is_empty() {
 998             return;
 999         }
1000
1001         for &module in &[&paths::KW_MODULE, &paths::SYM_MODULE] {
1002             if let Some(def_id) = def_path_res(cx, module).opt_def_id() {
1003                 for item in cx.tcx.module_children(def_id).iter() {
1004                     if_chain! {
1005                         if let Res::Def(DefKind::Const, item_def_id) = item.res;
1006                         let ty = cx.tcx.type_of(item_def_id);
1007                         if match_type(cx, ty, &paths::SYMBOL);
1008                         if let Ok(ConstValue::Scalar(value)) = cx.tcx.const_eval_poly(item_def_id);
1009                         if let Ok(value) = value.to_u32();
1010                         then {
1011                             self.symbol_map.insert(value, item_def_id);
1012                         }
1013                     }
1014                 }
1015             }
1016         }
1017     }
1018
1019     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1020         if_chain! {
1021             if let ExprKind::Call(func, [arg]) = &expr.kind;
1022             if let ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(func).kind();
1023             if match_def_path(cx, *def_id, &paths::SYMBOL_INTERN);
1024             if let Some(Constant::Str(arg)) = constant_simple(cx, cx.typeck_results(), arg);
1025             let value = Symbol::intern(&arg).as_u32();
1026             if let Some(&def_id) = self.symbol_map.get(&value);
1027             then {
1028                 span_lint_and_sugg(
1029                     cx,
1030                     INTERNING_DEFINED_SYMBOL,
1031                     is_expn_of(expr.span, "sym").unwrap_or(expr.span),
1032                     "interning a defined symbol",
1033                     "try",
1034                     cx.tcx.def_path_str(def_id),
1035                     Applicability::MachineApplicable,
1036                 );
1037             }
1038         }
1039         if let ExprKind::Binary(op, left, right) = expr.kind {
1040             if matches!(op.node, BinOpKind::Eq | BinOpKind::Ne) {
1041                 let data = [
1042                     (left, self.symbol_str_expr(left, cx)),
1043                     (right, self.symbol_str_expr(right, cx)),
1044                 ];
1045                 match data {
1046                     // both operands are a symbol string
1047                     [(_, Some(left)), (_, Some(right))] => {
1048                         span_lint_and_sugg(
1049                             cx,
1050                             UNNECESSARY_SYMBOL_STR,
1051                             expr.span,
1052                             "unnecessary `Symbol` to string conversion",
1053                             "try",
1054                             format!(
1055                                 "{} {} {}",
1056                                 left.as_symbol_snippet(cx),
1057                                 op.node.as_str(),
1058                                 right.as_symbol_snippet(cx),
1059                             ),
1060                             Applicability::MachineApplicable,
1061                         );
1062                     },
1063                     // one of the operands is a symbol string
1064                     [(expr, Some(symbol)), _] | [_, (expr, Some(symbol))] => {
1065                         // creating an owned string for comparison
1066                         if matches!(symbol, SymbolStrExpr::Expr { is_to_owned: true, .. }) {
1067                             span_lint_and_sugg(
1068                                 cx,
1069                                 UNNECESSARY_SYMBOL_STR,
1070                                 expr.span,
1071                                 "unnecessary string allocation",
1072                                 "try",
1073                                 format!("{}.as_str()", symbol.as_symbol_snippet(cx)),
1074                                 Applicability::MachineApplicable,
1075                             );
1076                         }
1077                     },
1078                     // nothing found
1079                     [(_, None), (_, None)] => {},
1080                 }
1081             }
1082         }
1083     }
1084 }
1085
1086 impl InterningDefinedSymbol {
1087     fn symbol_str_expr<'tcx>(&self, expr: &'tcx Expr<'tcx>, cx: &LateContext<'tcx>) -> Option<SymbolStrExpr<'tcx>> {
1088         static IDENT_STR_PATHS: &[&[&str]] = &[&paths::IDENT_AS_STR, &paths::TO_STRING_METHOD];
1089         static SYMBOL_STR_PATHS: &[&[&str]] = &[
1090             &paths::SYMBOL_AS_STR,
1091             &paths::SYMBOL_TO_IDENT_STRING,
1092             &paths::TO_STRING_METHOD,
1093         ];
1094         let call = if_chain! {
1095             if let ExprKind::AddrOf(_, _, e) = expr.kind;
1096             if let ExprKind::Unary(UnOp::Deref, e) = e.kind;
1097             then { e } else { expr }
1098         };
1099         if_chain! {
1100             // is a method call
1101             if let ExprKind::MethodCall(_, [item], _) = call.kind;
1102             if let Some(did) = cx.typeck_results().type_dependent_def_id(call.hir_id);
1103             let ty = cx.typeck_results().expr_ty(item);
1104             // ...on either an Ident or a Symbol
1105             if let Some(is_ident) = if match_type(cx, ty, &paths::SYMBOL) {
1106                 Some(false)
1107             } else if match_type(cx, ty, &paths::IDENT) {
1108                 Some(true)
1109             } else {
1110                 None
1111             };
1112             // ...which converts it to a string
1113             let paths = if is_ident { IDENT_STR_PATHS } else { SYMBOL_STR_PATHS };
1114             if let Some(path) = paths.iter().find(|path| match_def_path(cx, did, path));
1115             then {
1116                 let is_to_owned = path.last().unwrap().ends_with("string");
1117                 return Some(SymbolStrExpr::Expr {
1118                     item,
1119                     is_ident,
1120                     is_to_owned,
1121                 });
1122             }
1123         }
1124         // is a string constant
1125         if let Some(Constant::Str(s)) = constant_simple(cx, cx.typeck_results(), expr) {
1126             let value = Symbol::intern(&s).as_u32();
1127             // ...which matches a symbol constant
1128             if let Some(&def_id) = self.symbol_map.get(&value) {
1129                 return Some(SymbolStrExpr::Const(def_id));
1130             }
1131         }
1132         None
1133     }
1134 }
1135
1136 enum SymbolStrExpr<'tcx> {
1137     /// a string constant with a corresponding symbol constant
1138     Const(DefId),
1139     /// a "symbol to string" expression like `symbol.as_str()`
1140     Expr {
1141         /// part that evaluates to `Symbol` or `Ident`
1142         item: &'tcx Expr<'tcx>,
1143         is_ident: bool,
1144         /// whether an owned `String` is created like `to_ident_string()`
1145         is_to_owned: bool,
1146     },
1147 }
1148
1149 impl<'tcx> SymbolStrExpr<'tcx> {
1150     /// Returns a snippet that evaluates to a `Symbol` and is const if possible
1151     fn as_symbol_snippet(&self, cx: &LateContext<'_>) -> Cow<'tcx, str> {
1152         match *self {
1153             Self::Const(def_id) => cx.tcx.def_path_str(def_id).into(),
1154             Self::Expr { item, is_ident, .. } => {
1155                 let mut snip = snippet(cx, item.span.source_callsite(), "..");
1156                 if is_ident {
1157                     // get `Ident.name`
1158                     snip.to_mut().push_str(".name");
1159                 }
1160                 snip
1161             },
1162         }
1163     }
1164 }
1165
1166 declare_lint_pass!(IfChainStyle => [IF_CHAIN_STYLE]);
1167
1168 impl<'tcx> LateLintPass<'tcx> for IfChainStyle {
1169     fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
1170         let (local, after, if_chain_span) = if_chain! {
1171             if let [Stmt { kind: StmtKind::Local(local), .. }, after @ ..] = block.stmts;
1172             if let Some(if_chain_span) = is_expn_of(block.span, "if_chain");
1173             then { (local, after, if_chain_span) } else { return }
1174         };
1175         if is_first_if_chain_expr(cx, block.hir_id, if_chain_span) {
1176             span_lint(
1177                 cx,
1178                 IF_CHAIN_STYLE,
1179                 if_chain_local_span(cx, local, if_chain_span),
1180                 "`let` expression should be above the `if_chain!`",
1181             );
1182         } else if local.span.ctxt() == block.span.ctxt() && is_if_chain_then(after, block.expr, if_chain_span) {
1183             span_lint(
1184                 cx,
1185                 IF_CHAIN_STYLE,
1186                 if_chain_local_span(cx, local, if_chain_span),
1187                 "`let` expression should be inside `then { .. }`",
1188             );
1189         }
1190     }
1191
1192     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
1193         let (cond, then, els) = if let Some(higher::IfOrIfLet { cond, r#else, then }) = higher::IfOrIfLet::hir(expr) {
1194             (cond, then, r#else.is_some())
1195         } else {
1196             return;
1197         };
1198         let then_block = match then.kind {
1199             ExprKind::Block(block, _) => block,
1200             _ => return,
1201         };
1202         let if_chain_span = is_expn_of(expr.span, "if_chain");
1203         if !els {
1204             check_nested_if_chains(cx, expr, then_block, if_chain_span);
1205         }
1206         let if_chain_span = match if_chain_span {
1207             None => return,
1208             Some(span) => span,
1209         };
1210         // check for `if a && b;`
1211         if_chain! {
1212             if let ExprKind::Binary(op, _, _) = cond.kind;
1213             if op.node == BinOpKind::And;
1214             if cx.sess().source_map().is_multiline(cond.span);
1215             then {
1216                 span_lint(cx, IF_CHAIN_STYLE, cond.span, "`if a && b;` should be `if a; if b;`");
1217             }
1218         }
1219         if is_first_if_chain_expr(cx, expr.hir_id, if_chain_span)
1220             && is_if_chain_then(then_block.stmts, then_block.expr, if_chain_span)
1221         {
1222             span_lint(cx, IF_CHAIN_STYLE, expr.span, "`if_chain!` only has one `if`");
1223         }
1224     }
1225 }
1226
1227 fn check_nested_if_chains(
1228     cx: &LateContext<'_>,
1229     if_expr: &Expr<'_>,
1230     then_block: &Block<'_>,
1231     if_chain_span: Option<Span>,
1232 ) {
1233     #[rustfmt::skip]
1234     let (head, tail) = match *then_block {
1235         Block { stmts, expr: Some(tail), .. } => (stmts, tail),
1236         Block {
1237             stmts: &[
1238                 ref head @ ..,
1239                 Stmt { kind: StmtKind::Expr(tail) | StmtKind::Semi(tail), .. }
1240             ],
1241             ..
1242         } => (head, tail),
1243         _ => return,
1244     };
1245     if_chain! {
1246         if let Some(higher::IfOrIfLet { r#else: None, .. }) = higher::IfOrIfLet::hir(tail);
1247         let sm = cx.sess().source_map();
1248         if head
1249             .iter()
1250             .all(|stmt| matches!(stmt.kind, StmtKind::Local(..)) && !sm.is_multiline(stmt.span));
1251         if if_chain_span.is_some() || !is_else_clause(cx.tcx, if_expr);
1252         then {} else { return }
1253     }
1254     let (span, msg) = match (if_chain_span, is_expn_of(tail.span, "if_chain")) {
1255         (None, Some(_)) => (if_expr.span, "this `if` can be part of the inner `if_chain!`"),
1256         (Some(_), None) => (tail.span, "this `if` can be part of the outer `if_chain!`"),
1257         (Some(a), Some(b)) if a != b => (b, "this `if_chain!` can be merged with the outer `if_chain!`"),
1258         _ => return,
1259     };
1260     span_lint_and_then(cx, IF_CHAIN_STYLE, span, msg, |diag| {
1261         let (span, msg) = match head {
1262             [] => return,
1263             [stmt] => (stmt.span, "this `let` statement can also be in the `if_chain!`"),
1264             [a, .., b] => (
1265                 a.span.to(b.span),
1266                 "these `let` statements can also be in the `if_chain!`",
1267             ),
1268         };
1269         diag.span_help(span, msg);
1270     });
1271 }
1272
1273 fn is_first_if_chain_expr(cx: &LateContext<'_>, hir_id: HirId, if_chain_span: Span) -> bool {
1274     cx.tcx
1275         .hir()
1276         .parent_iter(hir_id)
1277         .find(|(_, node)| {
1278             #[rustfmt::skip]
1279             !matches!(node, Node::Expr(Expr { kind: ExprKind::Block(..), .. }) | Node::Stmt(_))
1280         })
1281         .map_or(false, |(id, _)| {
1282             is_expn_of(cx.tcx.hir().span(id), "if_chain") != Some(if_chain_span)
1283         })
1284 }
1285
1286 /// Checks a trailing slice of statements and expression of a `Block` to see if they are part
1287 /// of the `then {..}` portion of an `if_chain!`
1288 fn is_if_chain_then(stmts: &[Stmt<'_>], expr: Option<&Expr<'_>>, if_chain_span: Span) -> bool {
1289     let span = if let [stmt, ..] = stmts {
1290         stmt.span
1291     } else if let Some(expr) = expr {
1292         expr.span
1293     } else {
1294         // empty `then {}`
1295         return true;
1296     };
1297     is_expn_of(span, "if_chain").map_or(true, |span| span != if_chain_span)
1298 }
1299
1300 /// Creates a `Span` for `let x = ..;` in an `if_chain!` call.
1301 fn if_chain_local_span(cx: &LateContext<'_>, local: &Local<'_>, if_chain_span: Span) -> Span {
1302     let mut span = local.pat.span;
1303     if let Some(init) = local.init {
1304         span = span.to(init.span);
1305     }
1306     span.adjust(if_chain_span.ctxt().outer_expn());
1307     let sm = cx.sess().source_map();
1308     let span = sm.span_extend_to_prev_str(span, "let", false, true).unwrap_or(span);
1309     let span = sm.span_extend_to_next_char(span, ';', false);
1310     Span::new(
1311         span.lo() - BytePos(3),
1312         span.hi() + BytePos(1),
1313         span.ctxt(),
1314         span.parent(),
1315     )
1316 }