src/tools/clippy/clippy_lints/src/attrs.rs

   1 //! checks for attributes
   2
   3 use crate::utils::{
   4     first_line_of_span, is_present_in_source, match_def_path, paths, snippet_opt, span_lint, span_lint_and_help,
   5     span_lint_and_sugg, span_lint_and_then, without_block_comments,
   6 };
   7 use if_chain::if_chain;
   8 use rustc_ast::util::lev_distance::find_best_match_for_name;
   9 use rustc_ast::{AttrKind, AttrStyle, Attribute, Lit, LitKind, MetaItemKind, NestedMetaItem};
  10 use rustc_errors::Applicability;
  11 use rustc_hir::{
  12     Block, Expr, ExprKind, ImplItem, ImplItemKind, Item, ItemKind, StmtKind, TraitFn, TraitItem, TraitItemKind,
  13 };
  14 use rustc_lint::{CheckLintNameResult, EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
  15 use rustc_middle::lint::in_external_macro;
  16 use rustc_middle::ty;
  17 use rustc_session::{declare_lint_pass, declare_tool_lint};
  18 use rustc_span::source_map::Span;
  19 use rustc_span::symbol::{Symbol, SymbolStr};
  20 use semver::Version;
  21
  22 static UNIX_SYSTEMS: &[&str] = &[
  23     "android",
  24     "dragonfly",
  25     "emscripten",
  26     "freebsd",
  27     "fuchsia",
  28     "haiku",
  29     "illumos",
  30     "ios",
  31     "l4re",
  32     "linux",
  33     "macos",
  34     "netbsd",
  35     "openbsd",
  36     "redox",
  37     "solaris",
  38     "vxworks",
  39 ];
  40
  41 // NOTE: windows is excluded from the list because it's also a valid target family.
  42 static NON_UNIX_SYSTEMS: &[&str] = &["cloudabi", "hermit", "none", "wasi"];
  43
  44 declare_clippy_lint! {
  45     /// **What it does:** Checks for items annotated with `#[inline(always)]`,
  46     /// unless the annotated function is empty or simply panics.
  47     ///
  48     /// **Why is this bad?** While there are valid uses of this annotation (and once
  49     /// you know when to use it, by all means `allow` this lint), it's a common
  50     /// newbie-mistake to pepper one's code with it.
  51     ///
  52     /// As a rule of thumb, before slapping `#[inline(always)]` on a function,
  53     /// measure if that additional function call really affects your runtime profile
  54     /// sufficiently to make up for the increase in compile time.
  55     ///
  56     /// **Known problems:** False positives, big time. This lint is meant to be
  57     /// deactivated by everyone doing serious performance work. This means having
  58     /// done the measurement.
  59     ///
  60     /// **Example:**
  61     /// ```ignore
  62     /// #[inline(always)]
  63     /// fn not_quite_hot_code(..) { ... }
  64     /// ```
  65     pub INLINE_ALWAYS,
  66     pedantic,
  67     "use of `#[inline(always)]`"
  68 }
  69
  70 declare_clippy_lint! {
  71     /// **What it does:** Checks for `extern crate` and `use` items annotated with
  72     /// lint attributes.
  73     ///
  74     /// This lint permits `#[allow(unused_imports)]`, `#[allow(deprecated)]` and
  75     /// `#[allow(unreachable_pub)]` on `use` items and `#[allow(unused_imports)]` on
  76     /// `extern crate` items with a `#[macro_use]` attribute.
  77     ///
  78     /// **Why is this bad?** Lint attributes have no effect on crate imports. Most
  79     /// likely a `!` was forgotten.
  80     ///
  81     /// **Known problems:** None.
  82     ///
  83     /// **Example:**
  84     /// ```ignore
  85     /// // Bad
  86     /// #[deny(dead_code)]
  87     /// extern crate foo;
  88     /// #[forbid(dead_code)]
  89     /// use foo::bar;
  90     ///
  91     /// // Ok
  92     /// #[allow(unused_imports)]
  93     /// use foo::baz;
  94     /// #[allow(unused_imports)]
  95     /// #[macro_use]
  96     /// extern crate baz;
  97     /// ```
  98     pub USELESS_ATTRIBUTE,
  99     correctness,
 100     "use of lint attributes on `extern crate` items"
 101 }
 102
 103 declare_clippy_lint! {
 104     /// **What it does:** Checks for `#[deprecated]` annotations with a `since`
 105     /// field that is not a valid semantic version.
 106     ///
 107     /// **Why is this bad?** For checking the version of the deprecation, it must be
 108     /// a valid semver. Failing that, the contained information is useless.
 109     ///
 110     /// **Known problems:** None.
 111     ///
 112     /// **Example:**
 113     /// ```rust
 114     /// #[deprecated(since = "forever")]
 115     /// fn something_else() { /* ... */ }
 116     /// ```
 117     pub DEPRECATED_SEMVER,
 118     correctness,
 119     "use of `#[deprecated(since = \"x\")]` where x is not semver"
 120 }
 121
 122 declare_clippy_lint! {
 123     /// **What it does:** Checks for empty lines after outer attributes
 124     ///
 125     /// **Why is this bad?**
 126     /// Most likely the attribute was meant to be an inner attribute using a '!'.
 127     /// If it was meant to be an outer attribute, then the following item
 128     /// should not be separated by empty lines.
 129     ///
 130     /// **Known problems:** Can cause false positives.
 131     ///
 132     /// From the clippy side it's difficult to detect empty lines between an attributes and the
 133     /// following item because empty lines and comments are not part of the AST. The parsing
 134     /// currently works for basic cases but is not perfect.
 135     ///
 136     /// **Example:**
 137     /// ```rust
 138     /// // Good (as inner attribute)
 139     /// #![inline(always)]
 140     ///
 141     /// fn this_is_fine() { }
 142     ///
 143     /// // Bad
 144     /// #[inline(always)]
 145     ///
 146     /// fn not_quite_good_code() { }
 147     ///
 148     /// // Good (as outer attribute)
 149     /// #[inline(always)]
 150     /// fn this_is_fine_too() { }
 151     /// ```
 152     pub EMPTY_LINE_AFTER_OUTER_ATTR,
 153     nursery,
 154     "empty line after outer attribute"
 155 }
 156
 157 declare_clippy_lint! {
 158     /// **What it does:** Checks for `allow`/`warn`/`deny`/`forbid` attributes with scoped clippy
 159     /// lints and if those lints exist in clippy. If there is an uppercase letter in the lint name
 160     /// (not the tool name) and a lowercase version of this lint exists, it will suggest to lowercase
 161     /// the lint name.
 162     ///
 163     /// **Why is this bad?** A lint attribute with a mistyped lint name won't have an effect.
 164     ///
 165     /// **Known problems:** None.
 166     ///
 167     /// **Example:**
 168     /// Bad:
 169     /// ```rust
 170     /// #![warn(if_not_els)]
 171     /// #![deny(clippy::All)]
 172     /// ```
 173     ///
 174     /// Good:
 175     /// ```rust
 176     /// #![warn(if_not_else)]
 177     /// #![deny(clippy::all)]
 178     /// ```
 179     pub UNKNOWN_CLIPPY_LINTS,
 180     style,
 181     "unknown_lints for scoped Clippy lints"
 182 }
 183
 184 declare_clippy_lint! {
 185     /// **What it does:** Checks for `warn`/`deny`/`forbid` attributes targeting the whole clippy::restriction category.
 186     ///
 187     /// **Why is this bad?** Restriction lints sometimes are in contrast with other lints or even go against idiomatic rust.
 188     /// These lints should only be enabled on a lint-by-lint basis and with careful consideration.
 189     ///
 190     /// **Known problems:** None.
 191     ///
 192     /// **Example:**
 193     /// Bad:
 194     /// ```rust
 195     /// #![deny(clippy::restriction)]
 196     /// ```
 197     ///
 198     /// Good:
 199     /// ```rust
 200     /// #![deny(clippy::as_conversions)]
 201     /// ```
 202     pub BLANKET_CLIPPY_RESTRICTION_LINTS,
 203     style,
 204     "enabling the complete restriction group"
 205 }
 206
 207 declare_clippy_lint! {
 208     /// **What it does:** Checks for `#[cfg_attr(rustfmt, rustfmt_skip)]` and suggests to replace it
 209     /// with `#[rustfmt::skip]`.
 210     ///
 211     /// **Why is this bad?** Since tool_attributes ([rust-lang/rust#44690](https://github.com/rust-lang/rust/issues/44690))
 212     /// are stable now, they should be used instead of the old `cfg_attr(rustfmt)` attributes.
 213     ///
 214     /// **Known problems:** This lint doesn't detect crate level inner attributes, because they get
 215     /// processed before the PreExpansionPass lints get executed. See
 216     /// [#3123](https://github.com/rust-lang/rust-clippy/pull/3123#issuecomment-422321765)
 217     ///
 218     /// **Example:**
 219     ///
 220     /// Bad:
 221     /// ```rust
 222     /// #[cfg_attr(rustfmt, rustfmt_skip)]
 223     /// fn main() { }
 224     /// ```
 225     ///
 226     /// Good:
 227     /// ```rust
 228     /// #[rustfmt::skip]
 229     /// fn main() { }
 230     /// ```
 231     pub DEPRECATED_CFG_ATTR,
 232     complexity,
 233     "usage of `cfg_attr(rustfmt)` instead of tool attributes"
 234 }
 235
 236 declare_clippy_lint! {
 237     /// **What it does:** Checks for cfg attributes having operating systems used in target family position.
 238     ///
 239     /// **Why is this bad?** The configuration option will not be recognised and the related item will not be included
 240     /// by the conditional compilation engine.
 241     ///
 242     /// **Known problems:** None.
 243     ///
 244     /// **Example:**
 245     ///
 246     /// Bad:
 247     /// ```rust
 248     /// #[cfg(linux)]
 249     /// fn conditional() { }
 250     /// ```
 251     ///
 252     /// Good:
 253     /// ```rust
 254     /// #[cfg(target_os = "linux")]
 255     /// fn conditional() { }
 256     /// ```
 257     ///
 258     /// Or:
 259     /// ```rust
 260     /// #[cfg(unix)]
 261     /// fn conditional() { }
 262     /// ```
 263     /// Check the [Rust Reference](https://doc.rust-lang.org/reference/conditional-compilation.html#target_os) for more details.
 264     pub MISMATCHED_TARGET_OS,
 265     correctness,
 266     "usage of `cfg(operating_system)` instead of `cfg(target_os = \"operating_system\")`"
 267 }
 268
 269 declare_lint_pass!(Attributes => [
 270     INLINE_ALWAYS,
 271     DEPRECATED_SEMVER,
 272     USELESS_ATTRIBUTE,
 273     UNKNOWN_CLIPPY_LINTS,
 274     BLANKET_CLIPPY_RESTRICTION_LINTS,
 275 ]);
 276
 277 impl<'tcx> LateLintPass<'tcx> for Attributes {
 278     fn check_attribute(&mut self, cx: &LateContext<'tcx>, attr: &'tcx Attribute) {
 279         if let Some(items) = &attr.meta_item_list() {
 280             if let Some(ident) = attr.ident() {
 281                 let ident = &*ident.as_str();
 282                 match ident {
 283                     "allow" | "warn" | "deny" | "forbid" => {
 284                         check_clippy_lint_names(cx, ident, items);
 285                     },
 286                     _ => {},
 287                 }
 288                 if items.is_empty() || !attr.has_name(sym!(deprecated)) {
 289                     return;
 290                 }
 291                 for item in items {
 292                     if_chain! {
 293                         if let NestedMetaItem::MetaItem(mi) = &item;
 294                         if let MetaItemKind::NameValue(lit) = &mi.kind;
 295                         if mi.has_name(sym!(since));
 296                         then {
 297                             check_semver(cx, item.span(), lit);
 298                         }
 299                     }
 300                 }
 301             }
 302         }
 303     }
 304
 305     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 306         if is_relevant_item(cx, item) {
 307             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 308         }
 309         match item.kind {
 310             ItemKind::ExternCrate(..) | ItemKind::Use(..) => {
 311                 let skip_unused_imports = item.attrs.iter().any(|attr| attr.has_name(sym!(macro_use)));
 312
 313                 for attr in item.attrs {
 314                     if in_external_macro(cx.sess(), attr.span) {
 315                         return;
 316                     }
 317                     if let Some(lint_list) = &attr.meta_item_list() {
 318                         if let Some(ident) = attr.ident() {
 319                             match &*ident.as_str() {
 320                                 "allow" | "warn" | "deny" | "forbid" => {
 321                                     // permit `unused_imports`, `deprecated` and `unreachable_pub` for `use` items
 322                                     // and `unused_imports` for `extern crate` items with `macro_use`
 323                                     for lint in lint_list {
 324                                         match item.kind {
 325                                             ItemKind::Use(..) => {
 326                                                 if is_word(lint, sym!(unused_imports))
 327                                                     || is_word(lint, sym!(deprecated))
 328                                                     || is_word(lint, sym!(unreachable_pub))
 329                                                     || is_word(lint, sym!(unused))
 330                                                 {
 331                                                     return;
 332                                                 }
 333                                             },
 334                                             ItemKind::ExternCrate(..) => {
 335                                                 if is_word(lint, sym!(unused_imports)) && skip_unused_imports {
 336                                                     return;
 337                                                 }
 338                                                 if is_word(lint, sym!(unused_extern_crates)) {
 339                                                     return;
 340                                                 }
 341                                             },
 342                                             _ => {},
 343                                         }
 344                                     }
 345                                     let line_span = first_line_of_span(cx, attr.span);
 346
 347                                     if let Some(mut sugg) = snippet_opt(cx, line_span) {
 348                                         if sugg.contains("#[") {
 349                                             span_lint_and_then(
 350                                                 cx,
 351                                                 USELESS_ATTRIBUTE,
 352                                                 line_span,
 353                                                 "useless lint attribute",
 354                                                 |diag| {
 355                                                     sugg = sugg.replacen("#[", "#![", 1);
 356                                                     diag.span_suggestion(
 357                                                         line_span,
 358                                                         "if you just forgot a `!`, use",
 359                                                         sugg,
 360                                                         Applicability::MaybeIncorrect,
 361                                                     );
 362                                                 },
 363                                             );
 364                                         }
 365                                     }
 366                                 },
 367                                 _ => {},
 368                             }
 369                         }
 370                     }
 371                 }
 372             },
 373             _ => {},
 374         }
 375     }
 376
 377     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
 378         if is_relevant_impl(cx, item) {
 379             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 380         }
 381     }
 382
 383     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
 384         if is_relevant_trait(cx, item) {
 385             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 386         }
 387     }
 388 }
 389
 390 fn check_clippy_lint_names(cx: &LateContext<'_>, ident: &str, items: &[NestedMetaItem]) {
 391     fn extract_name(lint: &NestedMetaItem) -> Option<SymbolStr> {
 392         if_chain! {
 393             if let Some(meta_item) = lint.meta_item();
 394             if meta_item.path.segments.len() > 1;
 395             if let tool_name = meta_item.path.segments[0].ident;
 396             if tool_name.as_str() == "clippy";
 397             let lint_name = meta_item.path.segments.last().unwrap().ident.name;
 398             then {
 399                 return Some(lint_name.as_str());
 400             }
 401         }
 402         None
 403     }
 404
 405     let lint_store = cx.lints();
 406     for lint in items {
 407         if let Some(lint_name) = extract_name(lint) {
 408             if let CheckLintNameResult::Tool(Err((None, _))) =
 409                 lint_store.check_lint_name(&lint_name, Some(sym!(clippy)))
 410             {
 411                 span_lint_and_then(
 412                     cx,
 413                     UNKNOWN_CLIPPY_LINTS,
 414                     lint.span(),
 415                     &format!("unknown clippy lint: clippy::{}", lint_name),
 416                     |diag| {
 417                         let name_lower = lint_name.to_lowercase();
 418                         let symbols = lint_store
 419                             .get_lints()
 420                             .iter()
 421                             .map(|l| Symbol::intern(&l.name_lower()))
 422                             .collect::<Vec<_>>();
 423                         let sugg = find_best_match_for_name(
 424                             symbols.iter(),
 425                             Symbol::intern(&format!("clippy::{}", name_lower)),
 426                             None,
 427                         );
 428                         if lint_name.chars().any(char::is_uppercase)
 429                             && lint_store.find_lints(&format!("clippy::{}", name_lower)).is_ok()
 430                         {
 431                             diag.span_suggestion(
 432                                 lint.span(),
 433                                 "lowercase the lint name",
 434                                 format!("clippy::{}", name_lower),
 435                                 Applicability::MachineApplicable,
 436                             );
 437                         } else if let Some(sugg) = sugg {
 438                             diag.span_suggestion(
 439                                 lint.span(),
 440                                 "did you mean",
 441                                 sugg.to_string(),
 442                                 Applicability::MachineApplicable,
 443                             );
 444                         }
 445                     },
 446                 );
 447             } else if lint_name == "restriction" && ident != "allow" {
 448                 span_lint_and_help(
 449                     cx,
 450                     BLANKET_CLIPPY_RESTRICTION_LINTS,
 451                     lint.span(),
 452                     "restriction lints are not meant to be all enabled",
 453                     None,
 454                     "try enabling only the lints you really need",
 455                 );
 456             }
 457         }
 458     }
 459 }
 460
 461 fn is_relevant_item(cx: &LateContext<'_>, item: &Item<'_>) -> bool {
 462     if let ItemKind::Fn(_, _, eid) = item.kind {
 463         is_relevant_expr(cx, cx.tcx.typeck_body(eid), &cx.tcx.hir().body(eid).value)
 464     } else {
 465         true
 466     }
 467 }
 468
 469 fn is_relevant_impl(cx: &LateContext<'_>, item: &ImplItem<'_>) -> bool {
 470     match item.kind {
 471         ImplItemKind::Fn(_, eid) => is_relevant_expr(cx, cx.tcx.typeck_body(eid), &cx.tcx.hir().body(eid).value),
 472         _ => false,
 473     }
 474 }
 475
 476 fn is_relevant_trait(cx: &LateContext<'_>, item: &TraitItem<'_>) -> bool {
 477     match item.kind {
 478         TraitItemKind::Fn(_, TraitFn::Required(_)) => true,
 479         TraitItemKind::Fn(_, TraitFn::Provided(eid)) => {
 480             is_relevant_expr(cx, cx.tcx.typeck_body(eid), &cx.tcx.hir().body(eid).value)
 481         },
 482         _ => false,
 483     }
 484 }
 485
 486 fn is_relevant_block(cx: &LateContext<'_>, typeck_results: &ty::TypeckResults<'_>, block: &Block<'_>) -> bool {
 487     block.stmts.first().map_or(
 488         block
 489             .expr
 490             .as_ref()
 491             .map_or(false, |e| is_relevant_expr(cx, typeck_results, e)),
 492         |stmt| match &stmt.kind {
 493             StmtKind::Local(_) => true,
 494             StmtKind::Expr(expr) | StmtKind::Semi(expr) => is_relevant_expr(cx, typeck_results, expr),
 495             _ => false,
 496         },
 497     )
 498 }
 499
 500 fn is_relevant_expr(cx: &LateContext<'_>, typeck_results: &ty::TypeckResults<'_>, expr: &Expr<'_>) -> bool {
 501     match &expr.kind {
 502         ExprKind::Block(block, _) => is_relevant_block(cx, typeck_results, block),
 503         ExprKind::Ret(Some(e)) => is_relevant_expr(cx, typeck_results, e),
 504         ExprKind::Ret(None) | ExprKind::Break(_, None) => false,
 505         ExprKind::Call(path_expr, _) => {
 506             if let ExprKind::Path(qpath) = &path_expr.kind {
 507                 typeck_results
 508                     .qpath_res(qpath, path_expr.hir_id)
 509                     .opt_def_id()
 510                     .map_or(true, |fun_id| !match_def_path(cx, fun_id, &paths::BEGIN_PANIC))
 511             } else {
 512                 true
 513             }
 514         },
 515         _ => true,
 516     }
 517 }
 518
 519 fn check_attrs(cx: &LateContext<'_>, span: Span, name: Symbol, attrs: &[Attribute]) {
 520     if span.from_expansion() {
 521         return;
 522     }
 523
 524     for attr in attrs {
 525         if let Some(values) = attr.meta_item_list() {
 526             if values.len() != 1 || !attr.has_name(sym!(inline)) {
 527                 continue;
 528             }
 529             if is_word(&values[0], sym!(always)) {
 530                 span_lint(
 531                     cx,
 532                     INLINE_ALWAYS,
 533                     attr.span,
 534                     &format!(
 535                         "you have declared `#[inline(always)]` on `{}`. This is usually a bad idea",
 536                         name
 537                     ),
 538                 );
 539             }
 540         }
 541     }
 542 }
 543
 544 fn check_semver(cx: &LateContext<'_>, span: Span, lit: &Lit) {
 545     if let LitKind::Str(is, _) = lit.kind {
 546         if Version::parse(&is.as_str()).is_ok() {
 547             return;
 548         }
 549     }
 550     span_lint(
 551         cx,
 552         DEPRECATED_SEMVER,
 553         span,
 554         "the since field must contain a semver-compliant version",
 555     );
 556 }
 557
 558 fn is_word(nmi: &NestedMetaItem, expected: Symbol) -> bool {
 559     if let NestedMetaItem::MetaItem(mi) = &nmi {
 560         mi.is_word() && mi.has_name(expected)
 561     } else {
 562         false
 563     }
 564 }
 565
 566 declare_lint_pass!(EarlyAttributes => [
 567     DEPRECATED_CFG_ATTR,
 568     MISMATCHED_TARGET_OS,
 569     EMPTY_LINE_AFTER_OUTER_ATTR,
 570 ]);
 571
 572 impl EarlyLintPass for EarlyAttributes {
 573     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &rustc_ast::Item) {
 574         check_empty_line_after_outer_attr(cx, item);
 575     }
 576
 577     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &Attribute) {
 578         check_deprecated_cfg_attr(cx, attr);
 579         check_mismatched_target_os(cx, attr);
 580     }
 581 }
 582
 583 fn check_empty_line_after_outer_attr(cx: &EarlyContext<'_>, item: &rustc_ast::Item) {
 584     for attr in &item.attrs {
 585         let attr_item = if let AttrKind::Normal(ref attr) = attr.kind {
 586             attr
 587         } else {
 588             return;
 589         };
 590
 591         if attr.style == AttrStyle::Outer {
 592             if attr_item.args.inner_tokens().is_empty() || !is_present_in_source(cx, attr.span) {
 593                 return;
 594             }
 595
 596             let begin_of_attr_to_item = Span::new(attr.span.lo(), item.span.lo(), item.span.ctxt());
 597             let end_of_attr_to_item = Span::new(attr.span.hi(), item.span.lo(), item.span.ctxt());
 598
 599             if let Some(snippet) = snippet_opt(cx, end_of_attr_to_item) {
 600                 let lines = snippet.split('\n').collect::<Vec<_>>();
 601                 let lines = without_block_comments(lines);
 602
 603                 if lines.iter().filter(|l| l.trim().is_empty()).count() > 2 {
 604                     span_lint(
 605                         cx,
 606                         EMPTY_LINE_AFTER_OUTER_ATTR,
 607                         begin_of_attr_to_item,
 608                         "found an empty line after an outer attribute. \
 609                         Perhaps you forgot to add a `!` to make it an inner attribute?",
 610                     );
 611                 }
 612             }
 613         }
 614     }
 615 }
 616
 617 fn check_deprecated_cfg_attr(cx: &EarlyContext<'_>, attr: &Attribute) {
 618     if_chain! {
 619         // check cfg_attr
 620         if attr.has_name(sym!(cfg_attr));
 621         if let Some(items) = attr.meta_item_list();
 622         if items.len() == 2;
 623         // check for `rustfmt`
 624         if let Some(feature_item) = items[0].meta_item();
 625         if feature_item.has_name(sym!(rustfmt));
 626         // check for `rustfmt_skip` and `rustfmt::skip`
 627         if let Some(skip_item) = &items[1].meta_item();
 628         if skip_item.has_name(sym!(rustfmt_skip)) ||
 629             skip_item.path.segments.last().expect("empty path in attribute").ident.name == sym!(skip);
 630         // Only lint outer attributes, because custom inner attributes are unstable
 631         // Tracking issue: https://github.com/rust-lang/rust/issues/54726
 632         if let AttrStyle::Outer = attr.style;
 633         then {
 634             span_lint_and_sugg(
 635                 cx,
 636                 DEPRECATED_CFG_ATTR,
 637                 attr.span,
 638                 "`cfg_attr` is deprecated for rustfmt and got replaced by tool attributes",
 639                 "use",
 640                 "#[rustfmt::skip]".to_string(),
 641                 Applicability::MachineApplicable,
 642             );
 643         }
 644     }
 645 }
 646
 647 fn check_mismatched_target_os(cx: &EarlyContext<'_>, attr: &Attribute) {
 648     fn find_os(name: &str) -> Option<&'static str> {
 649         UNIX_SYSTEMS
 650             .iter()
 651             .chain(NON_UNIX_SYSTEMS.iter())
 652             .find(|&&os| os == name)
 653             .copied()
 654     }
 655
 656     fn is_unix(name: &str) -> bool {
 657         UNIX_SYSTEMS.iter().any(|&os| os == name)
 658     }
 659
 660     fn find_mismatched_target_os(items: &[NestedMetaItem]) -> Vec<(&str, Span)> {
 661         let mut mismatched = Vec::new();
 662
 663         for item in items {
 664             if let NestedMetaItem::MetaItem(meta) = item {
 665                 match &meta.kind {
 666                     MetaItemKind::List(list) => {
 667                         mismatched.extend(find_mismatched_target_os(&list));
 668                     },
 669                     MetaItemKind::Word => {
 670                         if_chain! {
 671                             if let Some(ident) = meta.ident();
 672                             if let Some(os) = find_os(&*ident.name.as_str());
 673                             then {
 674                                 mismatched.push((os, ident.span));
 675                             }
 676                         }
 677                     },
 678                     _ => {},
 679                 }
 680             }
 681         }
 682
 683         mismatched
 684     }
 685
 686     if_chain! {
 687         if attr.has_name(sym!(cfg));
 688         if let Some(list) = attr.meta_item_list();
 689         let mismatched = find_mismatched_target_os(&list);
 690         if !mismatched.is_empty();
 691         then {
 692             let mess = "operating system used in target family position";
 693
 694             span_lint_and_then(cx, MISMATCHED_TARGET_OS, attr.span, &mess, |diag| {
 695                 // Avoid showing the unix suggestion multiple times in case
 696                 // we have more than one mismatch for unix-like systems
 697                 let mut unix_suggested = false;
 698
 699                 for (os, span) in mismatched {
 700                     let sugg = format!("target_os = \"{}\"", os);
 701                     diag.span_suggestion(span, "try", sugg, Applicability::MaybeIncorrect);
 702
 703                     if !unix_suggested && is_unix(os) {
 704                         diag.help("Did you mean `unix`?");
 705                         unix_suggested = true;
 706                     }
 707                 }
 708             });
 709         }
 710     }
 711 }