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)]`,
  75     /// `#[allow(unreachable_pub)]`, `#[allow(clippy::wildcard_imports)]` and
  76     /// `#[allow(clippy::enum_glob_use)]` on `use` items and `#[allow(unused_imports)]` on
  77     /// `extern crate` items with a `#[macro_use]` attribute.
  78     ///
  79     /// **Why is this bad?** Lint attributes have no effect on crate imports. Most
  80     /// likely a `!` was forgotten.
  81     ///
  82     /// **Known problems:** None.
  83     ///
  84     /// **Example:**
  85     /// ```ignore
  86     /// // Bad
  87     /// #[deny(dead_code)]
  88     /// extern crate foo;
  89     /// #[forbid(dead_code)]
  90     /// use foo::bar;
  91     ///
  92     /// // Ok
  93     /// #[allow(unused_imports)]
  94     /// use foo::baz;
  95     /// #[allow(unused_imports)]
  96     /// #[macro_use]
  97     /// extern crate baz;
  98     /// ```
  99     pub USELESS_ATTRIBUTE,
 100     correctness,
 101     "use of lint attributes on `extern crate` items"
 102 }
 103
 104 declare_clippy_lint! {
 105     /// **What it does:** Checks for `#[deprecated]` annotations with a `since`
 106     /// field that is not a valid semantic version.
 107     ///
 108     /// **Why is this bad?** For checking the version of the deprecation, it must be
 109     /// a valid semver. Failing that, the contained information is useless.
 110     ///
 111     /// **Known problems:** None.
 112     ///
 113     /// **Example:**
 114     /// ```rust
 115     /// #[deprecated(since = "forever")]
 116     /// fn something_else() { /* ... */ }
 117     /// ```
 118     pub DEPRECATED_SEMVER,
 119     correctness,
 120     "use of `#[deprecated(since = \"x\")]` where x is not semver"
 121 }
 122
 123 declare_clippy_lint! {
 124     /// **What it does:** Checks for empty lines after outer attributes
 125     ///
 126     /// **Why is this bad?**
 127     /// Most likely the attribute was meant to be an inner attribute using a '!'.
 128     /// If it was meant to be an outer attribute, then the following item
 129     /// should not be separated by empty lines.
 130     ///
 131     /// **Known problems:** Can cause false positives.
 132     ///
 133     /// From the clippy side it's difficult to detect empty lines between an attributes and the
 134     /// following item because empty lines and comments are not part of the AST. The parsing
 135     /// currently works for basic cases but is not perfect.
 136     ///
 137     /// **Example:**
 138     /// ```rust
 139     /// // Good (as inner attribute)
 140     /// #![allow(dead_code)]
 141     ///
 142     /// fn this_is_fine() { }
 143     ///
 144     /// // Bad
 145     /// #[allow(dead_code)]
 146     ///
 147     /// fn not_quite_good_code() { }
 148     ///
 149     /// // Good (as outer attribute)
 150     /// #[allow(dead_code)]
 151     /// fn this_is_fine_too() { }
 152     /// ```
 153     pub EMPTY_LINE_AFTER_OUTER_ATTR,
 154     nursery,
 155     "empty line after outer attribute"
 156 }
 157
 158 declare_clippy_lint! {
 159     /// **What it does:** Checks for `allow`/`warn`/`deny`/`forbid` attributes with scoped clippy
 160     /// lints and if those lints exist in clippy. If there is an uppercase letter in the lint name
 161     /// (not the tool name) and a lowercase version of this lint exists, it will suggest to lowercase
 162     /// the lint name.
 163     ///
 164     /// **Why is this bad?** A lint attribute with a mistyped lint name won't have an effect.
 165     ///
 166     /// **Known problems:** None.
 167     ///
 168     /// **Example:**
 169     /// Bad:
 170     /// ```rust
 171     /// #![warn(if_not_els)]
 172     /// #![deny(clippy::All)]
 173     /// ```
 174     ///
 175     /// Good:
 176     /// ```rust
 177     /// #![warn(if_not_else)]
 178     /// #![deny(clippy::all)]
 179     /// ```
 180     pub UNKNOWN_CLIPPY_LINTS,
 181     style,
 182     "unknown_lints for scoped Clippy lints"
 183 }
 184
 185 declare_clippy_lint! {
 186     /// **What it does:** Checks for `warn`/`deny`/`forbid` attributes targeting the whole clippy::restriction category.
 187     ///
 188     /// **Why is this bad?** Restriction lints sometimes are in contrast with other lints or even go against idiomatic rust.
 189     /// These lints should only be enabled on a lint-by-lint basis and with careful consideration.
 190     ///
 191     /// **Known problems:** None.
 192     ///
 193     /// **Example:**
 194     /// Bad:
 195     /// ```rust
 196     /// #![deny(clippy::restriction)]
 197     /// ```
 198     ///
 199     /// Good:
 200     /// ```rust
 201     /// #![deny(clippy::as_conversions)]
 202     /// ```
 203     pub BLANKET_CLIPPY_RESTRICTION_LINTS,
 204     style,
 205     "enabling the complete restriction group"
 206 }
 207
 208 declare_clippy_lint! {
 209     /// **What it does:** Checks for `#[cfg_attr(rustfmt, rustfmt_skip)]` and suggests to replace it
 210     /// with `#[rustfmt::skip]`.
 211     ///
 212     /// **Why is this bad?** Since tool_attributes ([rust-lang/rust#44690](https://github.com/rust-lang/rust/issues/44690))
 213     /// are stable now, they should be used instead of the old `cfg_attr(rustfmt)` attributes.
 214     ///
 215     /// **Known problems:** This lint doesn't detect crate level inner attributes, because they get
 216     /// processed before the PreExpansionPass lints get executed. See
 217     /// [#3123](https://github.com/rust-lang/rust-clippy/pull/3123#issuecomment-422321765)
 218     ///
 219     /// **Example:**
 220     ///
 221     /// Bad:
 222     /// ```rust
 223     /// #[cfg_attr(rustfmt, rustfmt_skip)]
 224     /// fn main() { }
 225     /// ```
 226     ///
 227     /// Good:
 228     /// ```rust
 229     /// #[rustfmt::skip]
 230     /// fn main() { }
 231     /// ```
 232     pub DEPRECATED_CFG_ATTR,
 233     complexity,
 234     "usage of `cfg_attr(rustfmt)` instead of tool attributes"
 235 }
 236
 237 declare_clippy_lint! {
 238     /// **What it does:** Checks for cfg attributes having operating systems used in target family position.
 239     ///
 240     /// **Why is this bad?** The configuration option will not be recognised and the related item will not be included
 241     /// by the conditional compilation engine.
 242     ///
 243     /// **Known problems:** None.
 244     ///
 245     /// **Example:**
 246     ///
 247     /// Bad:
 248     /// ```rust
 249     /// #[cfg(linux)]
 250     /// fn conditional() { }
 251     /// ```
 252     ///
 253     /// Good:
 254     /// ```rust
 255     /// #[cfg(target_os = "linux")]
 256     /// fn conditional() { }
 257     /// ```
 258     ///
 259     /// Or:
 260     /// ```rust
 261     /// #[cfg(unix)]
 262     /// fn conditional() { }
 263     /// ```
 264     /// Check the [Rust Reference](https://doc.rust-lang.org/reference/conditional-compilation.html#target_os) for more details.
 265     pub MISMATCHED_TARGET_OS,
 266     correctness,
 267     "usage of `cfg(operating_system)` instead of `cfg(target_os = \"operating_system\")`"
 268 }
 269
 270 declare_lint_pass!(Attributes => [
 271     INLINE_ALWAYS,
 272     DEPRECATED_SEMVER,
 273     USELESS_ATTRIBUTE,
 274     UNKNOWN_CLIPPY_LINTS,
 275     BLANKET_CLIPPY_RESTRICTION_LINTS,
 276 ]);
 277
 278 impl<'tcx> LateLintPass<'tcx> for Attributes {
 279     fn check_attribute(&mut self, cx: &LateContext<'tcx>, attr: &'tcx Attribute) {
 280         if let Some(items) = &attr.meta_item_list() {
 281             if let Some(ident) = attr.ident() {
 282                 let ident = &*ident.as_str();
 283                 match ident {
 284                     "allow" | "warn" | "deny" | "forbid" => {
 285                         check_clippy_lint_names(cx, ident, items);
 286                     },
 287                     _ => {},
 288                 }
 289                 if items.is_empty() || !attr.has_name(sym!(deprecated)) {
 290                     return;
 291                 }
 292                 for item in items {
 293                     if_chain! {
 294                         if let NestedMetaItem::MetaItem(mi) = &item;
 295                         if let MetaItemKind::NameValue(lit) = &mi.kind;
 296                         if mi.has_name(sym!(since));
 297                         then {
 298                             check_semver(cx, item.span(), lit);
 299                         }
 300                     }
 301                 }
 302             }
 303         }
 304     }
 305
 306     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 307         if is_relevant_item(cx, item) {
 308             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 309         }
 310         match item.kind {
 311             ItemKind::ExternCrate(..) | ItemKind::Use(..) => {
 312                 let skip_unused_imports = item.attrs.iter().any(|attr| attr.has_name(sym!(macro_use)));
 313
 314                 for attr in item.attrs {
 315                     if in_external_macro(cx.sess(), attr.span) {
 316                         return;
 317                     }
 318                     if let Some(lint_list) = &attr.meta_item_list() {
 319                         if let Some(ident) = attr.ident() {
 320                             match &*ident.as_str() {
 321                                 "allow" | "warn" | "deny" | "forbid" => {
 322                                     // permit `unused_imports`, `deprecated`, `unreachable_pub`,
 323                                     // `clippy::wildcard_imports`, and `clippy::enum_glob_use` for `use` items
 324                                     // and `unused_imports` for `extern crate` items with `macro_use`
 325                                     for lint in lint_list {
 326                                         match item.kind {
 327                                             ItemKind::Use(..) => {
 328                                                 if is_word(lint, sym!(unused_imports))
 329                                                     || is_word(lint, sym!(deprecated))
 330                                                     || is_word(lint, sym!(unreachable_pub))
 331                                                     || is_word(lint, sym!(unused))
 332                                                     || extract_clippy_lint(lint)
 333                                                         .map_or(false, |s| s == "wildcard_imports")
 334                                                     || extract_clippy_lint(lint).map_or(false, |s| s == "enum_glob_use")
 335                                                 {
 336                                                     return;
 337                                                 }
 338                                             },
 339                                             ItemKind::ExternCrate(..) => {
 340                                                 if is_word(lint, sym!(unused_imports)) && skip_unused_imports {
 341                                                     return;
 342                                                 }
 343                                                 if is_word(lint, sym!(unused_extern_crates)) {
 344                                                     return;
 345                                                 }
 346                                             },
 347                                             _ => {},
 348                                         }
 349                                     }
 350                                     let line_span = first_line_of_span(cx, attr.span);
 351
 352                                     if let Some(mut sugg) = snippet_opt(cx, line_span) {
 353                                         if sugg.contains("#[") {
 354                                             span_lint_and_then(
 355                                                 cx,
 356                                                 USELESS_ATTRIBUTE,
 357                                                 line_span,
 358                                                 "useless lint attribute",
 359                                                 |diag| {
 360                                                     sugg = sugg.replacen("#[", "#![", 1);
 361                                                     diag.span_suggestion(
 362                                                         line_span,
 363                                                         "if you just forgot a `!`, use",
 364                                                         sugg,
 365                                                         Applicability::MaybeIncorrect,
 366                                                     );
 367                                                 },
 368                                             );
 369                                         }
 370                                     }
 371                                 },
 372                                 _ => {},
 373                             }
 374                         }
 375                     }
 376                 }
 377             },
 378             _ => {},
 379         }
 380     }
 381
 382     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
 383         if is_relevant_impl(cx, item) {
 384             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 385         }
 386     }
 387
 388     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
 389         if is_relevant_trait(cx, item) {
 390             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 391         }
 392     }
 393 }
 394
 395 /// Returns the lint name if it is clippy lint.
 396 fn extract_clippy_lint(lint: &NestedMetaItem) -> Option<SymbolStr> {
 397     if_chain! {
 398         if let Some(meta_item) = lint.meta_item();
 399         if meta_item.path.segments.len() > 1;
 400         if let tool_name = meta_item.path.segments[0].ident;
 401         if tool_name.as_str() == "clippy";
 402         let lint_name = meta_item.path.segments.last().unwrap().ident.name;
 403         then {
 404             return Some(lint_name.as_str());
 405         }
 406     }
 407     None
 408 }
 409
 410 fn check_clippy_lint_names(cx: &LateContext<'_>, ident: &str, items: &[NestedMetaItem]) {
 411     let lint_store = cx.lints();
 412     for lint in items {
 413         if let Some(lint_name) = extract_clippy_lint(lint) {
 414             if let CheckLintNameResult::Tool(Err((None, _))) =
 415                 lint_store.check_lint_name(&lint_name, Some(sym!(clippy)))
 416             {
 417                 span_lint_and_then(
 418                     cx,
 419                     UNKNOWN_CLIPPY_LINTS,
 420                     lint.span(),
 421                     &format!("unknown clippy lint: clippy::{}", lint_name),
 422                     |diag| {
 423                         let name_lower = lint_name.to_lowercase();
 424                         let symbols = lint_store
 425                             .get_lints()
 426                             .iter()
 427                             .map(|l| Symbol::intern(&l.name_lower()))
 428                             .collect::<Vec<_>>();
 429                         let sugg = find_best_match_for_name(
 430                             symbols.iter(),
 431                             Symbol::intern(&format!("clippy::{}", name_lower)),
 432                             None,
 433                         );
 434                         if lint_name.chars().any(char::is_uppercase)
 435                             && lint_store.find_lints(&format!("clippy::{}", name_lower)).is_ok()
 436                         {
 437                             diag.span_suggestion(
 438                                 lint.span(),
 439                                 "lowercase the lint name",
 440                                 format!("clippy::{}", name_lower),
 441                                 Applicability::MachineApplicable,
 442                             );
 443                         } else if let Some(sugg) = sugg {
 444                             diag.span_suggestion(
 445                                 lint.span(),
 446                                 "did you mean",
 447                                 sugg.to_string(),
 448                                 Applicability::MachineApplicable,
 449                             );
 450                         }
 451                     },
 452                 );
 453             } else if lint_name == "restriction" && ident != "allow" {
 454                 span_lint_and_help(
 455                     cx,
 456                     BLANKET_CLIPPY_RESTRICTION_LINTS,
 457                     lint.span(),
 458                     "restriction lints are not meant to be all enabled",
 459                     None,
 460                     "try enabling only the lints you really need",
 461                 );
 462             }
 463         }
 464     }
 465 }
 466
 467 fn is_relevant_item(cx: &LateContext<'_>, item: &Item<'_>) -> bool {
 468     if let ItemKind::Fn(_, _, eid) = item.kind {
 469         is_relevant_expr(cx, cx.tcx.typeck_body(eid), &cx.tcx.hir().body(eid).value)
 470     } else {
 471         true
 472     }
 473 }
 474
 475 fn is_relevant_impl(cx: &LateContext<'_>, item: &ImplItem<'_>) -> bool {
 476     match item.kind {
 477         ImplItemKind::Fn(_, eid) => is_relevant_expr(cx, cx.tcx.typeck_body(eid), &cx.tcx.hir().body(eid).value),
 478         _ => false,
 479     }
 480 }
 481
 482 fn is_relevant_trait(cx: &LateContext<'_>, item: &TraitItem<'_>) -> bool {
 483     match item.kind {
 484         TraitItemKind::Fn(_, TraitFn::Required(_)) => true,
 485         TraitItemKind::Fn(_, TraitFn::Provided(eid)) => {
 486             is_relevant_expr(cx, cx.tcx.typeck_body(eid), &cx.tcx.hir().body(eid).value)
 487         },
 488         _ => false,
 489     }
 490 }
 491
 492 fn is_relevant_block(cx: &LateContext<'_>, typeck_results: &ty::TypeckResults<'_>, block: &Block<'_>) -> bool {
 493     block.stmts.first().map_or(
 494         block
 495             .expr
 496             .as_ref()
 497             .map_or(false, |e| is_relevant_expr(cx, typeck_results, e)),
 498         |stmt| match &stmt.kind {
 499             StmtKind::Local(_) => true,
 500             StmtKind::Expr(expr) | StmtKind::Semi(expr) => is_relevant_expr(cx, typeck_results, expr),
 501             _ => false,
 502         },
 503     )
 504 }
 505
 506 fn is_relevant_expr(cx: &LateContext<'_>, typeck_results: &ty::TypeckResults<'_>, expr: &Expr<'_>) -> bool {
 507     match &expr.kind {
 508         ExprKind::Block(block, _) => is_relevant_block(cx, typeck_results, block),
 509         ExprKind::Ret(Some(e)) => is_relevant_expr(cx, typeck_results, e),
 510         ExprKind::Ret(None) | ExprKind::Break(_, None) => false,
 511         ExprKind::Call(path_expr, _) => {
 512             if let ExprKind::Path(qpath) = &path_expr.kind {
 513                 typeck_results
 514                     .qpath_res(qpath, path_expr.hir_id)
 515                     .opt_def_id()
 516                     .map_or(true, |fun_id| !match_def_path(cx, fun_id, &paths::BEGIN_PANIC))
 517             } else {
 518                 true
 519             }
 520         },
 521         _ => true,
 522     }
 523 }
 524
 525 fn check_attrs(cx: &LateContext<'_>, span: Span, name: Symbol, attrs: &[Attribute]) {
 526     if span.from_expansion() {
 527         return;
 528     }
 529
 530     for attr in attrs {
 531         if let Some(values) = attr.meta_item_list() {
 532             if values.len() != 1 || !attr.has_name(sym!(inline)) {
 533                 continue;
 534             }
 535             if is_word(&values[0], sym!(always)) {
 536                 span_lint(
 537                     cx,
 538                     INLINE_ALWAYS,
 539                     attr.span,
 540                     &format!(
 541                         "you have declared `#[inline(always)]` on `{}`. This is usually a bad idea",
 542                         name
 543                     ),
 544                 );
 545             }
 546         }
 547     }
 548 }
 549
 550 fn check_semver(cx: &LateContext<'_>, span: Span, lit: &Lit) {
 551     if let LitKind::Str(is, _) = lit.kind {
 552         if Version::parse(&is.as_str()).is_ok() {
 553             return;
 554         }
 555     }
 556     span_lint(
 557         cx,
 558         DEPRECATED_SEMVER,
 559         span,
 560         "the since field must contain a semver-compliant version",
 561     );
 562 }
 563
 564 fn is_word(nmi: &NestedMetaItem, expected: Symbol) -> bool {
 565     if let NestedMetaItem::MetaItem(mi) = &nmi {
 566         mi.is_word() && mi.has_name(expected)
 567     } else {
 568         false
 569     }
 570 }
 571
 572 declare_lint_pass!(EarlyAttributes => [
 573     DEPRECATED_CFG_ATTR,
 574     MISMATCHED_TARGET_OS,
 575     EMPTY_LINE_AFTER_OUTER_ATTR,
 576 ]);
 577
 578 impl EarlyLintPass for EarlyAttributes {
 579     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &rustc_ast::Item) {
 580         check_empty_line_after_outer_attr(cx, item);
 581     }
 582
 583     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &Attribute) {
 584         check_deprecated_cfg_attr(cx, attr);
 585         check_mismatched_target_os(cx, attr);
 586     }
 587 }
 588
 589 fn check_empty_line_after_outer_attr(cx: &EarlyContext<'_>, item: &rustc_ast::Item) {
 590     for attr in &item.attrs {
 591         let attr_item = if let AttrKind::Normal(ref attr) = attr.kind {
 592             attr
 593         } else {
 594             return;
 595         };
 596
 597         if attr.style == AttrStyle::Outer {
 598             if attr_item.args.inner_tokens().is_empty() || !is_present_in_source(cx, attr.span) {
 599                 return;
 600             }
 601
 602             let begin_of_attr_to_item = Span::new(attr.span.lo(), item.span.lo(), item.span.ctxt());
 603             let end_of_attr_to_item = Span::new(attr.span.hi(), item.span.lo(), item.span.ctxt());
 604
 605             if let Some(snippet) = snippet_opt(cx, end_of_attr_to_item) {
 606                 let lines = snippet.split('\n').collect::<Vec<_>>();
 607                 let lines = without_block_comments(lines);
 608
 609                 if lines.iter().filter(|l| l.trim().is_empty()).count() > 2 {
 610                     span_lint(
 611                         cx,
 612                         EMPTY_LINE_AFTER_OUTER_ATTR,
 613                         begin_of_attr_to_item,
 614                         "found an empty line after an outer attribute. \
 615                         Perhaps you forgot to add a `!` to make it an inner attribute?",
 616                     );
 617                 }
 618             }
 619         }
 620     }
 621 }
 622
 623 fn check_deprecated_cfg_attr(cx: &EarlyContext<'_>, attr: &Attribute) {
 624     if_chain! {
 625         // check cfg_attr
 626         if attr.has_name(sym!(cfg_attr));
 627         if let Some(items) = attr.meta_item_list();
 628         if items.len() == 2;
 629         // check for `rustfmt`
 630         if let Some(feature_item) = items[0].meta_item();
 631         if feature_item.has_name(sym!(rustfmt));
 632         // check for `rustfmt_skip` and `rustfmt::skip`
 633         if let Some(skip_item) = &items[1].meta_item();
 634         if skip_item.has_name(sym!(rustfmt_skip)) ||
 635             skip_item.path.segments.last().expect("empty path in attribute").ident.name == sym!(skip);
 636         // Only lint outer attributes, because custom inner attributes are unstable
 637         // Tracking issue: https://github.com/rust-lang/rust/issues/54726
 638         if let AttrStyle::Outer = attr.style;
 639         then {
 640             span_lint_and_sugg(
 641                 cx,
 642                 DEPRECATED_CFG_ATTR,
 643                 attr.span,
 644                 "`cfg_attr` is deprecated for rustfmt and got replaced by tool attributes",
 645                 "use",
 646                 "#[rustfmt::skip]".to_string(),
 647                 Applicability::MachineApplicable,
 648             );
 649         }
 650     }
 651 }
 652
 653 fn check_mismatched_target_os(cx: &EarlyContext<'_>, attr: &Attribute) {
 654     fn find_os(name: &str) -> Option<&'static str> {
 655         UNIX_SYSTEMS
 656             .iter()
 657             .chain(NON_UNIX_SYSTEMS.iter())
 658             .find(|&&os| os == name)
 659             .copied()
 660     }
 661
 662     fn is_unix(name: &str) -> bool {
 663         UNIX_SYSTEMS.iter().any(|&os| os == name)
 664     }
 665
 666     fn find_mismatched_target_os(items: &[NestedMetaItem]) -> Vec<(&str, Span)> {
 667         let mut mismatched = Vec::new();
 668
 669         for item in items {
 670             if let NestedMetaItem::MetaItem(meta) = item {
 671                 match &meta.kind {
 672                     MetaItemKind::List(list) => {
 673                         mismatched.extend(find_mismatched_target_os(&list));
 674                     },
 675                     MetaItemKind::Word => {
 676                         if_chain! {
 677                             if let Some(ident) = meta.ident();
 678                             if let Some(os) = find_os(&*ident.name.as_str());
 679                             then {
 680                                 mismatched.push((os, ident.span));
 681                             }
 682                         }
 683                     },
 684                     _ => {},
 685                 }
 686             }
 687         }
 688
 689         mismatched
 690     }
 691
 692     if_chain! {
 693         if attr.has_name(sym!(cfg));
 694         if let Some(list) = attr.meta_item_list();
 695         let mismatched = find_mismatched_target_os(&list);
 696         if !mismatched.is_empty();
 697         then {
 698             let mess = "operating system used in target family position";
 699
 700             span_lint_and_then(cx, MISMATCHED_TARGET_OS, attr.span, &mess, |diag| {
 701                 // Avoid showing the unix suggestion multiple times in case
 702                 // we have more than one mismatch for unix-like systems
 703                 let mut unix_suggested = false;
 704
 705                 for (os, span) in mismatched {
 706                     let sugg = format!("target_os = \"{}\"", os);
 707                     diag.span_suggestion(span, "try", sugg, Applicability::MaybeIncorrect);
 708
 709                     if !unix_suggested && is_unix(os) {
 710                         diag.help("Did you mean `unix`?");
 711                         unix_suggested = true;
 712                     }
 713                 }
 714             });
 715         }
 716     }
 717 }