clippy_lints/src/attrs.rs

   1 //! checks for attributes
   2
   3 use crate::utils::{
   4     first_line_of_span, is_present_in_source, match_panic_def_id, 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::sym;
  20 use rustc_span::symbol::{Symbol, SymbolStr};
  21 use semver::Version;
  22
  23 static UNIX_SYSTEMS: &[&str] = &[
  24     "android",
  25     "dragonfly",
  26     "emscripten",
  27     "freebsd",
  28     "fuchsia",
  29     "haiku",
  30     "illumos",
  31     "ios",
  32     "l4re",
  33     "linux",
  34     "macos",
  35     "netbsd",
  36     "openbsd",
  37     "redox",
  38     "solaris",
  39     "vxworks",
  40 ];
  41
  42 // NOTE: windows is excluded from the list because it's also a valid target family.
  43 static NON_UNIX_SYSTEMS: &[&str] = &["hermit", "none", "wasi"];
  44
  45 declare_clippy_lint! {
  46     /// **What it does:** Checks for items annotated with `#[inline(always)]`,
  47     /// unless the annotated function is empty or simply panics.
  48     ///
  49     /// **Why is this bad?** While there are valid uses of this annotation (and once
  50     /// you know when to use it, by all means `allow` this lint), it's a common
  51     /// newbie-mistake to pepper one's code with it.
  52     ///
  53     /// As a rule of thumb, before slapping `#[inline(always)]` on a function,
  54     /// measure if that additional function call really affects your runtime profile
  55     /// sufficiently to make up for the increase in compile time.
  56     ///
  57     /// **Known problems:** False positives, big time. This lint is meant to be
  58     /// deactivated by everyone doing serious performance work. This means having
  59     /// done the measurement.
  60     ///
  61     /// **Example:**
  62     /// ```ignore
  63     /// #[inline(always)]
  64     /// fn not_quite_hot_code(..) { ... }
  65     /// ```
  66     pub INLINE_ALWAYS,
  67     pedantic,
  68     "use of `#[inline(always)]`"
  69 }
  70
  71 declare_clippy_lint! {
  72     /// **What it does:** Checks for `extern crate` and `use` items annotated with
  73     /// lint attributes.
  74     ///
  75     /// This lint permits `#[allow(unused_imports)]`, `#[allow(deprecated)]`,
  76     /// `#[allow(unreachable_pub)]`, `#[allow(clippy::wildcard_imports)]` and
  77     /// `#[allow(clippy::enum_glob_use)]` on `use` items and `#[allow(unused_imports)]` on
  78     /// `extern crate` items with a `#[macro_use]` attribute.
  79     ///
  80     /// **Why is this bad?** Lint attributes have no effect on crate imports. Most
  81     /// likely a `!` was forgotten.
  82     ///
  83     /// **Known problems:** None.
  84     ///
  85     /// **Example:**
  86     /// ```ignore
  87     /// // Bad
  88     /// #[deny(dead_code)]
  89     /// extern crate foo;
  90     /// #[forbid(dead_code)]
  91     /// use foo::bar;
  92     ///
  93     /// // Ok
  94     /// #[allow(unused_imports)]
  95     /// use foo::baz;
  96     /// #[allow(unused_imports)]
  97     /// #[macro_use]
  98     /// extern crate baz;
  99     /// ```
 100     pub USELESS_ATTRIBUTE,
 101     correctness,
 102     "use of lint attributes on `extern crate` items"
 103 }
 104
 105 declare_clippy_lint! {
 106     /// **What it does:** Checks for `#[deprecated]` annotations with a `since`
 107     /// field that is not a valid semantic version.
 108     ///
 109     /// **Why is this bad?** For checking the version of the deprecation, it must be
 110     /// a valid semver. Failing that, the contained information is useless.
 111     ///
 112     /// **Known problems:** None.
 113     ///
 114     /// **Example:**
 115     /// ```rust
 116     /// #[deprecated(since = "forever")]
 117     /// fn something_else() { /* ... */ }
 118     /// ```
 119     pub DEPRECATED_SEMVER,
 120     correctness,
 121     "use of `#[deprecated(since = \"x\")]` where x is not semver"
 122 }
 123
 124 declare_clippy_lint! {
 125     /// **What it does:** Checks for empty lines after outer attributes
 126     ///
 127     /// **Why is this bad?**
 128     /// Most likely the attribute was meant to be an inner attribute using a '!'.
 129     /// If it was meant to be an outer attribute, then the following item
 130     /// should not be separated by empty lines.
 131     ///
 132     /// **Known problems:** Can cause false positives.
 133     ///
 134     /// From the clippy side it's difficult to detect empty lines between an attributes and the
 135     /// following item because empty lines and comments are not part of the AST. The parsing
 136     /// currently works for basic cases but is not perfect.
 137     ///
 138     /// **Example:**
 139     /// ```rust
 140     /// // Good (as inner attribute)
 141     /// #![allow(dead_code)]
 142     ///
 143     /// fn this_is_fine() { }
 144     ///
 145     /// // Bad
 146     /// #[allow(dead_code)]
 147     ///
 148     /// fn not_quite_good_code() { }
 149     ///
 150     /// // Good (as outer attribute)
 151     /// #[allow(dead_code)]
 152     /// fn this_is_fine_too() { }
 153     /// ```
 154     pub EMPTY_LINE_AFTER_OUTER_ATTR,
 155     nursery,
 156     "empty line after outer attribute"
 157 }
 158
 159 declare_clippy_lint! {
 160     /// **What it does:** Checks for `allow`/`warn`/`deny`/`forbid` attributes with scoped clippy
 161     /// lints and if those lints exist in clippy. If there is an uppercase letter in the lint name
 162     /// (not the tool name) and a lowercase version of this lint exists, it will suggest to lowercase
 163     /// the lint name.
 164     ///
 165     /// **Why is this bad?** A lint attribute with a mistyped lint name won't have an effect.
 166     ///
 167     /// **Known problems:** None.
 168     ///
 169     /// **Example:**
 170     /// Bad:
 171     /// ```rust
 172     /// #![warn(if_not_els)]
 173     /// #![deny(clippy::All)]
 174     /// ```
 175     ///
 176     /// Good:
 177     /// ```rust
 178     /// #![warn(if_not_else)]
 179     /// #![deny(clippy::all)]
 180     /// ```
 181     pub UNKNOWN_CLIPPY_LINTS,
 182     style,
 183     "unknown_lints for scoped Clippy lints"
 184 }
 185
 186 declare_clippy_lint! {
 187     /// **What it does:** Checks for `warn`/`deny`/`forbid` attributes targeting the whole clippy::restriction category.
 188     ///
 189     /// **Why is this bad?** Restriction lints sometimes are in contrast with other lints or even go against idiomatic rust.
 190     /// These lints should only be enabled on a lint-by-lint basis and with careful consideration.
 191     ///
 192     /// **Known problems:** None.
 193     ///
 194     /// **Example:**
 195     /// Bad:
 196     /// ```rust
 197     /// #![deny(clippy::restriction)]
 198     /// ```
 199     ///
 200     /// Good:
 201     /// ```rust
 202     /// #![deny(clippy::as_conversions)]
 203     /// ```
 204     pub BLANKET_CLIPPY_RESTRICTION_LINTS,
 205     style,
 206     "enabling the complete restriction group"
 207 }
 208
 209 declare_clippy_lint! {
 210     /// **What it does:** Checks for `#[cfg_attr(rustfmt, rustfmt_skip)]` and suggests to replace it
 211     /// with `#[rustfmt::skip]`.
 212     ///
 213     /// **Why is this bad?** Since tool_attributes ([rust-lang/rust#44690](https://github.com/rust-lang/rust/issues/44690))
 214     /// are stable now, they should be used instead of the old `cfg_attr(rustfmt)` attributes.
 215     ///
 216     /// **Known problems:** This lint doesn't detect crate level inner attributes, because they get
 217     /// processed before the PreExpansionPass lints get executed. See
 218     /// [#3123](https://github.com/rust-lang/rust-clippy/pull/3123#issuecomment-422321765)
 219     ///
 220     /// **Example:**
 221     ///
 222     /// Bad:
 223     /// ```rust
 224     /// #[cfg_attr(rustfmt, rustfmt_skip)]
 225     /// fn main() { }
 226     /// ```
 227     ///
 228     /// Good:
 229     /// ```rust
 230     /// #[rustfmt::skip]
 231     /// fn main() { }
 232     /// ```
 233     pub DEPRECATED_CFG_ATTR,
 234     complexity,
 235     "usage of `cfg_attr(rustfmt)` instead of tool attributes"
 236 }
 237
 238 declare_clippy_lint! {
 239     /// **What it does:** Checks for cfg attributes having operating systems used in target family position.
 240     ///
 241     /// **Why is this bad?** The configuration option will not be recognised and the related item will not be included
 242     /// by the conditional compilation engine.
 243     ///
 244     /// **Known problems:** None.
 245     ///
 246     /// **Example:**
 247     ///
 248     /// Bad:
 249     /// ```rust
 250     /// #[cfg(linux)]
 251     /// fn conditional() { }
 252     /// ```
 253     ///
 254     /// Good:
 255     /// ```rust
 256     /// #[cfg(target_os = "linux")]
 257     /// fn conditional() { }
 258     /// ```
 259     ///
 260     /// Or:
 261     /// ```rust
 262     /// #[cfg(unix)]
 263     /// fn conditional() { }
 264     /// ```
 265     /// Check the [Rust Reference](https://doc.rust-lang.org/reference/conditional-compilation.html#target_os) for more details.
 266     pub MISMATCHED_TARGET_OS,
 267     correctness,
 268     "usage of `cfg(operating_system)` instead of `cfg(target_os = \"operating_system\")`"
 269 }
 270
 271 declare_lint_pass!(Attributes => [
 272     INLINE_ALWAYS,
 273     DEPRECATED_SEMVER,
 274     USELESS_ATTRIBUTE,
 275     UNKNOWN_CLIPPY_LINTS,
 276     BLANKET_CLIPPY_RESTRICTION_LINTS,
 277 ]);
 278
 279 impl<'tcx> LateLintPass<'tcx> for Attributes {
 280     fn check_attribute(&mut self, cx: &LateContext<'tcx>, attr: &'tcx Attribute) {
 281         if let Some(items) = &attr.meta_item_list() {
 282             if let Some(ident) = attr.ident() {
 283                 let ident = &*ident.as_str();
 284                 match ident {
 285                     "allow" | "warn" | "deny" | "forbid" => {
 286                         check_clippy_lint_names(cx, ident, items);
 287                     },
 288                     _ => {},
 289                 }
 290                 if items.is_empty() || !attr.has_name(sym::deprecated) {
 291                     return;
 292                 }
 293                 for item in items {
 294                     if_chain! {
 295                         if let NestedMetaItem::MetaItem(mi) = &item;
 296                         if let MetaItemKind::NameValue(lit) = &mi.kind;
 297                         if mi.has_name(sym::since);
 298                         then {
 299                             check_semver(cx, item.span(), lit);
 300                         }
 301                     }
 302                 }
 303             }
 304         }
 305     }
 306
 307     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 308         if is_relevant_item(cx, item) {
 309             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 310         }
 311         match item.kind {
 312             ItemKind::ExternCrate(..) | ItemKind::Use(..) => {
 313                 let skip_unused_imports = item.attrs.iter().any(|attr| attr.has_name(sym::macro_use));
 314
 315                 for attr in item.attrs {
 316                     if in_external_macro(cx.sess(), attr.span) {
 317                         return;
 318                     }
 319                     if let Some(lint_list) = &attr.meta_item_list() {
 320                         if let Some(ident) = attr.ident() {
 321                             match &*ident.as_str() {
 322                                 "allow" | "warn" | "deny" | "forbid" => {
 323                                     // permit `unused_imports`, `deprecated`, `unreachable_pub`,
 324                                     // `clippy::wildcard_imports`, and `clippy::enum_glob_use` for `use` items
 325                                     // and `unused_imports` for `extern crate` items with `macro_use`
 326                                     for lint in lint_list {
 327                                         match item.kind {
 328                                             ItemKind::Use(..) => {
 329                                                 if is_word(lint, sym!(unused_imports))
 330                                                     || is_word(lint, sym::deprecated)
 331                                                     || is_word(lint, sym!(unreachable_pub))
 332                                                     || is_word(lint, sym!(unused))
 333                                                     || extract_clippy_lint(lint)
 334                                                         .map_or(false, |s| s == "wildcard_imports")
 335                                                     || extract_clippy_lint(lint).map_or(false, |s| s == "enum_glob_use")
 336                                                 {
 337                                                     return;
 338                                                 }
 339                                             },
 340                                             ItemKind::ExternCrate(..) => {
 341                                                 if is_word(lint, sym!(unused_imports)) && skip_unused_imports {
 342                                                     return;
 343                                                 }
 344                                                 if is_word(lint, sym!(unused_extern_crates)) {
 345                                                     return;
 346                                                 }
 347                                             },
 348                                             _ => {},
 349                                         }
 350                                     }
 351                                     let line_span = first_line_of_span(cx, attr.span);
 352
 353                                     if let Some(mut sugg) = snippet_opt(cx, line_span) {
 354                                         if sugg.contains("#[") {
 355                                             span_lint_and_then(
 356                                                 cx,
 357                                                 USELESS_ATTRIBUTE,
 358                                                 line_span,
 359                                                 "useless lint attribute",
 360                                                 |diag| {
 361                                                     sugg = sugg.replacen("#[", "#![", 1);
 362                                                     diag.span_suggestion(
 363                                                         line_span,
 364                                                         "if you just forgot a `!`, use",
 365                                                         sugg,
 366                                                         Applicability::MaybeIncorrect,
 367                                                     );
 368                                                 },
 369                                             );
 370                                         }
 371                                     }
 372                                 },
 373                                 _ => {},
 374                             }
 375                         }
 376                     }
 377                 }
 378             },
 379             _ => {},
 380         }
 381     }
 382
 383     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
 384         if is_relevant_impl(cx, item) {
 385             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 386         }
 387     }
 388
 389     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
 390         if is_relevant_trait(cx, item) {
 391             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 392         }
 393     }
 394 }
 395
 396 /// Returns the lint name if it is clippy lint.
 397 fn extract_clippy_lint(lint: &NestedMetaItem) -> Option<SymbolStr> {
 398     if_chain! {
 399         if let Some(meta_item) = lint.meta_item();
 400         if meta_item.path.segments.len() > 1;
 401         if let tool_name = meta_item.path.segments[0].ident;
 402         if tool_name.as_str() == "clippy";
 403         let lint_name = meta_item.path.segments.last().unwrap().ident.name;
 404         then {
 405             return Some(lint_name.as_str());
 406         }
 407     }
 408     None
 409 }
 410
 411 fn check_clippy_lint_names(cx: &LateContext<'_>, ident: &str, items: &[NestedMetaItem]) {
 412     let lint_store = cx.lints();
 413     for lint in items {
 414         if let Some(lint_name) = extract_clippy_lint(lint) {
 415             if let CheckLintNameResult::Tool(Err((None, _))) = 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_panic_def_id(cx, fun_id))
 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 }