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