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

   1 //! checks for attributes
   2
   3 use crate::reexport::Name;
   4 use crate::utils::{
   5     first_line_of_span, is_present_in_source, match_def_path, paths, snippet_opt, span_lint, span_lint_and_help,
   6     span_lint_and_sugg, span_lint_and_then, without_block_comments,
   7 };
   8 use if_chain::if_chain;
   9 use rustc_ast::ast::{AttrKind, AttrStyle, Attribute, Lit, LitKind, MetaItemKind, NestedMetaItem};
  10 use rustc_ast::util::lev_distance::find_best_match_for_name;
  11 use rustc_errors::Applicability;
  12 use rustc_hir::{
  13     Block, Expr, ExprKind, ImplItem, ImplItemKind, Item, ItemKind, StmtKind, TraitFn, TraitItem, TraitItemKind,
  14 };
  15 use rustc_lint::{CheckLintNameResult, EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
  16 use rustc_middle::lint::in_external_macro;
  17 use rustc_middle::ty;
  18 use rustc_session::{declare_lint_pass, declare_tool_lint};
  19 use rustc_span::source_map::Span;
  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] = &["cloudabi", "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)]` and
  76     /// `#[allow(unreachable_pub)]` 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     /// #![inline(always)]
 141     ///
 142     /// fn this_is_fine() { }
 143     ///
 144     /// // Bad
 145     /// #[inline(always)]
 146     ///
 147     /// fn not_quite_good_code() { }
 148     ///
 149     /// // Good (as outer attribute)
 150     /// #[inline(always)]
 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.check_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.check_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.check_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` and `unreachable_pub` for `use` items
 323                                     // and `unused_imports` for `extern crate` items with `macro_use`
 324                                     for lint in lint_list {
 325                                         match item.kind {
 326                                             ItemKind::Use(..) => {
 327                                                 if is_word(lint, sym!(unused_imports))
 328                                                     || is_word(lint, sym!(deprecated))
 329                                                     || is_word(lint, sym!(unreachable_pub))
 330                                                     || is_word(lint, sym!(unused))
 331                                                 {
 332                                                     return;
 333                                                 }
 334                                             },
 335                                             ItemKind::ExternCrate(..) => {
 336                                                 if is_word(lint, sym!(unused_imports)) && skip_unused_imports {
 337                                                     return;
 338                                                 }
 339                                                 if is_word(lint, sym!(unused_extern_crates)) {
 340                                                     return;
 341                                                 }
 342                                             },
 343                                             _ => {},
 344                                         }
 345                                     }
 346                                     let line_span = first_line_of_span(cx, attr.span);
 347
 348                                     if let Some(mut sugg) = snippet_opt(cx, line_span) {
 349                                         if sugg.contains("#[") {
 350                                             span_lint_and_then(
 351                                                 cx,
 352                                                 USELESS_ATTRIBUTE,
 353                                                 line_span,
 354                                                 "useless lint attribute",
 355                                                 |diag| {
 356                                                     sugg = sugg.replacen("#[", "#![", 1);
 357                                                     diag.span_suggestion(
 358                                                         line_span,
 359                                                         "if you just forgot a `!`, use",
 360                                                         sugg,
 361                                                         Applicability::MaybeIncorrect,
 362                                                     );
 363                                                 },
 364                                             );
 365                                         }
 366                                     }
 367                                 },
 368                                 _ => {},
 369                             }
 370                         }
 371                     }
 372                 }
 373             },
 374             _ => {},
 375         }
 376     }
 377
 378     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
 379         if is_relevant_impl(cx, item) {
 380             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 381         }
 382     }
 383
 384     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
 385         if is_relevant_trait(cx, item) {
 386             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 387         }
 388     }
 389 }
 390
 391 fn check_clippy_lint_names(cx: &LateContext<'_>, ident: &str, items: &[NestedMetaItem]) {
 392     fn extract_name(lint: &NestedMetaItem) -> Option<SymbolStr> {
 393         if_chain! {
 394             if let Some(meta_item) = lint.meta_item();
 395             if meta_item.path.segments.len() > 1;
 396             if let tool_name = meta_item.path.segments[0].ident;
 397             if tool_name.as_str() == "clippy";
 398             let lint_name = meta_item.path.segments.last().unwrap().ident.name;
 399             then {
 400                 return Some(lint_name.as_str());
 401             }
 402         }
 403         None
 404     }
 405
 406     let lint_store = cx.lints();
 407     for lint in items {
 408         if let Some(lint_name) = extract_name(lint) {
 409             if let CheckLintNameResult::Tool(Err((None, _))) =
 410                 lint_store.check_lint_name(&lint_name, Some(sym!(clippy)))
 411             {
 412                 span_lint_and_then(
 413                     cx,
 414                     UNKNOWN_CLIPPY_LINTS,
 415                     lint.span(),
 416                     &format!("unknown clippy lint: clippy::{}", lint_name),
 417                     |diag| {
 418                         let name_lower = lint_name.to_lowercase();
 419                         let symbols = lint_store
 420                             .get_lints()
 421                             .iter()
 422                             .map(|l| Symbol::intern(&l.name_lower()))
 423                             .collect::<Vec<_>>();
 424                         let sugg = find_best_match_for_name(symbols.iter(), &format!("clippy::{}", name_lower), None);
 425                         if lint_name.chars().any(char::is_uppercase)
 426                             && lint_store.find_lints(&format!("clippy::{}", name_lower)).is_ok()
 427                         {
 428                             diag.span_suggestion(
 429                                 lint.span(),
 430                                 "lowercase the lint name",
 431                                 format!("clippy::{}", name_lower),
 432                                 Applicability::MachineApplicable,
 433                             );
 434                         } else if let Some(sugg) = sugg {
 435                             diag.span_suggestion(
 436                                 lint.span(),
 437                                 "did you mean",
 438                                 sugg.to_string(),
 439                                 Applicability::MachineApplicable,
 440                             );
 441                         }
 442                     },
 443                 );
 444             } else if lint_name == "restriction" && ident != "allow" {
 445                 span_lint_and_help(
 446                     cx,
 447                     BLANKET_CLIPPY_RESTRICTION_LINTS,
 448                     lint.span(),
 449                     "restriction lints are not meant to be all enabled",
 450                     None,
 451                     "try enabling only the lints you really need",
 452                 );
 453             }
 454         }
 455     }
 456 }
 457
 458 fn is_relevant_item(cx: &LateContext<'_>, item: &Item<'_>) -> bool {
 459     if let ItemKind::Fn(_, _, eid) = item.kind {
 460         is_relevant_expr(cx, cx.tcx.body_tables(eid), &cx.tcx.hir().body(eid).value)
 461     } else {
 462         true
 463     }
 464 }
 465
 466 fn is_relevant_impl(cx: &LateContext<'_>, item: &ImplItem<'_>) -> bool {
 467     match item.kind {
 468         ImplItemKind::Fn(_, eid) => is_relevant_expr(cx, cx.tcx.body_tables(eid), &cx.tcx.hir().body(eid).value),
 469         _ => false,
 470     }
 471 }
 472
 473 fn is_relevant_trait(cx: &LateContext<'_>, item: &TraitItem<'_>) -> bool {
 474     match item.kind {
 475         TraitItemKind::Fn(_, TraitFn::Required(_)) => true,
 476         TraitItemKind::Fn(_, TraitFn::Provided(eid)) => {
 477             is_relevant_expr(cx, cx.tcx.body_tables(eid), &cx.tcx.hir().body(eid).value)
 478         },
 479         _ => false,
 480     }
 481 }
 482
 483 fn is_relevant_block(cx: &LateContext<'_>, tables: &ty::TypeckTables<'_>, block: &Block<'_>) -> bool {
 484     block.stmts.first().map_or(
 485         block.expr.as_ref().map_or(false, |e| is_relevant_expr(cx, tables, e)),
 486         |stmt| match &stmt.kind {
 487             StmtKind::Local(_) => true,
 488             StmtKind::Expr(expr) | StmtKind::Semi(expr) => is_relevant_expr(cx, tables, expr),
 489             _ => false,
 490         },
 491     )
 492 }
 493
 494 fn is_relevant_expr(cx: &LateContext<'_>, tables: &ty::TypeckTables<'_>, expr: &Expr<'_>) -> bool {
 495     match &expr.kind {
 496         ExprKind::Block(block, _) => is_relevant_block(cx, tables, block),
 497         ExprKind::Ret(Some(e)) => is_relevant_expr(cx, tables, e),
 498         ExprKind::Ret(None) | ExprKind::Break(_, None) => false,
 499         ExprKind::Call(path_expr, _) => {
 500             if let ExprKind::Path(qpath) = &path_expr.kind {
 501                 tables
 502                     .qpath_res(qpath, path_expr.hir_id)
 503                     .opt_def_id()
 504                     .map_or(true, |fun_id| !match_def_path(cx, fun_id, &paths::BEGIN_PANIC))
 505             } else {
 506                 true
 507             }
 508         },
 509         _ => true,
 510     }
 511 }
 512
 513 fn check_attrs(cx: &LateContext<'_>, span: Span, name: Name, attrs: &[Attribute]) {
 514     if span.from_expansion() {
 515         return;
 516     }
 517
 518     for attr in attrs {
 519         if let Some(values) = attr.meta_item_list() {
 520             if values.len() != 1 || !attr.check_name(sym!(inline)) {
 521                 continue;
 522             }
 523             if is_word(&values[0], sym!(always)) {
 524                 span_lint(
 525                     cx,
 526                     INLINE_ALWAYS,
 527                     attr.span,
 528                     &format!(
 529                         "you have declared `#[inline(always)]` on `{}`. This is usually a bad idea",
 530                         name
 531                     ),
 532                 );
 533             }
 534         }
 535     }
 536 }
 537
 538 fn check_semver(cx: &LateContext<'_>, span: Span, lit: &Lit) {
 539     if let LitKind::Str(is, _) = lit.kind {
 540         if Version::parse(&is.as_str()).is_ok() {
 541             return;
 542         }
 543     }
 544     span_lint(
 545         cx,
 546         DEPRECATED_SEMVER,
 547         span,
 548         "the since field must contain a semver-compliant version",
 549     );
 550 }
 551
 552 fn is_word(nmi: &NestedMetaItem, expected: Symbol) -> bool {
 553     if let NestedMetaItem::MetaItem(mi) = &nmi {
 554         mi.is_word() && mi.check_name(expected)
 555     } else {
 556         false
 557     }
 558 }
 559
 560 declare_lint_pass!(EarlyAttributes => [
 561     DEPRECATED_CFG_ATTR,
 562     MISMATCHED_TARGET_OS,
 563     EMPTY_LINE_AFTER_OUTER_ATTR,
 564 ]);
 565
 566 impl EarlyLintPass for EarlyAttributes {
 567     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &rustc_ast::ast::Item) {
 568         check_empty_line_after_outer_attr(cx, item);
 569     }
 570
 571     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &Attribute) {
 572         check_deprecated_cfg_attr(cx, attr);
 573         check_mismatched_target_os(cx, attr);
 574     }
 575 }
 576
 577 fn check_empty_line_after_outer_attr(cx: &EarlyContext<'_>, item: &rustc_ast::ast::Item) {
 578     for attr in &item.attrs {
 579         let attr_item = if let AttrKind::Normal(ref attr) = attr.kind {
 580             attr
 581         } else {
 582             return;
 583         };
 584
 585         if attr.style == AttrStyle::Outer {
 586             if attr_item.args.inner_tokens().is_empty() || !is_present_in_source(cx, attr.span) {
 587                 return;
 588             }
 589
 590             let begin_of_attr_to_item = Span::new(attr.span.lo(), item.span.lo(), item.span.ctxt());
 591             let end_of_attr_to_item = Span::new(attr.span.hi(), item.span.lo(), item.span.ctxt());
 592
 593             if let Some(snippet) = snippet_opt(cx, end_of_attr_to_item) {
 594                 let lines = snippet.split('\n').collect::<Vec<_>>();
 595                 let lines = without_block_comments(lines);
 596
 597                 if lines.iter().filter(|l| l.trim().is_empty()).count() > 2 {
 598                     span_lint(
 599                         cx,
 600                         EMPTY_LINE_AFTER_OUTER_ATTR,
 601                         begin_of_attr_to_item,
 602                         "Found an empty line after an outer attribute. \
 603                         Perhaps you forgot to add a `!` to make it an inner attribute?",
 604                     );
 605                 }
 606             }
 607         }
 608     }
 609 }
 610
 611 fn check_deprecated_cfg_attr(cx: &EarlyContext<'_>, attr: &Attribute) {
 612     if_chain! {
 613         // check cfg_attr
 614         if attr.check_name(sym!(cfg_attr));
 615         if let Some(items) = attr.meta_item_list();
 616         if items.len() == 2;
 617         // check for `rustfmt`
 618         if let Some(feature_item) = items[0].meta_item();
 619         if feature_item.check_name(sym!(rustfmt));
 620         // check for `rustfmt_skip` and `rustfmt::skip`
 621         if let Some(skip_item) = &items[1].meta_item();
 622         if skip_item.check_name(sym!(rustfmt_skip)) ||
 623             skip_item.path.segments.last().expect("empty path in attribute").ident.name == sym!(skip);
 624         // Only lint outer attributes, because custom inner attributes are unstable
 625         // Tracking issue: https://github.com/rust-lang/rust/issues/54726
 626         if let AttrStyle::Outer = attr.style;
 627         then {
 628             span_lint_and_sugg(
 629                 cx,
 630                 DEPRECATED_CFG_ATTR,
 631                 attr.span,
 632                 "`cfg_attr` is deprecated for rustfmt and got replaced by tool attributes",
 633                 "use",
 634                 "#[rustfmt::skip]".to_string(),
 635                 Applicability::MachineApplicable,
 636             );
 637         }
 638     }
 639 }
 640
 641 fn check_mismatched_target_os(cx: &EarlyContext<'_>, attr: &Attribute) {
 642     fn find_os(name: &str) -> Option<&'static str> {
 643         UNIX_SYSTEMS
 644             .iter()
 645             .chain(NON_UNIX_SYSTEMS.iter())
 646             .find(|&&os| os == name)
 647             .copied()
 648     }
 649
 650     fn is_unix(name: &str) -> bool {
 651         UNIX_SYSTEMS.iter().any(|&os| os == name)
 652     }
 653
 654     fn find_mismatched_target_os(items: &[NestedMetaItem]) -> Vec<(&str, Span)> {
 655         let mut mismatched = Vec::new();
 656
 657         for item in items {
 658             if let NestedMetaItem::MetaItem(meta) = item {
 659                 match &meta.kind {
 660                     MetaItemKind::List(list) => {
 661                         mismatched.extend(find_mismatched_target_os(&list));
 662                     },
 663                     MetaItemKind::Word => {
 664                         if_chain! {
 665                             if let Some(ident) = meta.ident();
 666                             if let Some(os) = find_os(&*ident.name.as_str());
 667                             then {
 668                                 mismatched.push((os, ident.span));
 669                             }
 670                         }
 671                     },
 672                     _ => {},
 673                 }
 674             }
 675         }
 676
 677         mismatched
 678     }
 679
 680     if_chain! {
 681         if attr.check_name(sym!(cfg));
 682         if let Some(list) = attr.meta_item_list();
 683         let mismatched = find_mismatched_target_os(&list);
 684         if !mismatched.is_empty();
 685         then {
 686             let mess = "operating system used in target family position";
 687
 688             span_lint_and_then(cx, MISMATCHED_TARGET_OS, attr.span, &mess, |diag| {
 689                 // Avoid showing the unix suggestion multiple times in case
 690                 // we have more than one mismatch for unix-like systems
 691                 let mut unix_suggested = false;
 692
 693                 for (os, span) in mismatched {
 694                     let sugg = format!("target_os = \"{}\"", os);
 695                     diag.span_suggestion(span, "try", sugg, Applicability::MaybeIncorrect);
 696
 697                     if !unix_suggested && is_unix(os) {
 698                         diag.help("Did you mean `unix`?");
 699                         unix_suggested = true;
 700                     }
 701                 }
 702             });
 703         }
 704     }
 705 }