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_sugg,
   6     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;
  21 use semver::Version;
  22
  23 declare_clippy_lint! {
  24     /// **What it does:** Checks for items annotated with `#[inline(always)]`,
  25     /// unless the annotated function is empty or simply panics.
  26     ///
  27     /// **Why is this bad?** While there are valid uses of this annotation (and once
  28     /// you know when to use it, by all means `allow` this lint), it's a common
  29     /// newbie-mistake to pepper one's code with it.
  30     ///
  31     /// As a rule of thumb, before slapping `#[inline(always)]` on a function,
  32     /// measure if that additional function call really affects your runtime profile
  33     /// sufficiently to make up for the increase in compile time.
  34     ///
  35     /// **Known problems:** False positives, big time. This lint is meant to be
  36     /// deactivated by everyone doing serious performance work. This means having
  37     /// done the measurement.
  38     ///
  39     /// **Example:**
  40     /// ```ignore
  41     /// #[inline(always)]
  42     /// fn not_quite_hot_code(..) { ... }
  43     /// ```
  44     pub INLINE_ALWAYS,
  45     pedantic,
  46     "use of `#[inline(always)]`"
  47 }
  48
  49 declare_clippy_lint! {
  50     /// **What it does:** Checks for `extern crate` and `use` items annotated with
  51     /// lint attributes.
  52     ///
  53     /// This lint whitelists `#[allow(unused_imports)]`, `#[allow(deprecated)]` and
  54     /// `#[allow(unreachable_pub)]` on `use` items and `#[allow(unused_imports)]` on
  55     /// `extern crate` items with a `#[macro_use]` attribute.
  56     ///
  57     /// **Why is this bad?** Lint attributes have no effect on crate imports. Most
  58     /// likely a `!` was forgotten.
  59     ///
  60     /// **Known problems:** None.
  61     ///
  62     /// **Example:**
  63     /// ```ignore
  64     /// // Bad
  65     /// #[deny(dead_code)]
  66     /// extern crate foo;
  67     /// #[forbid(dead_code)]
  68     /// use foo::bar;
  69     ///
  70     /// // Ok
  71     /// #[allow(unused_imports)]
  72     /// use foo::baz;
  73     /// #[allow(unused_imports)]
  74     /// #[macro_use]
  75     /// extern crate baz;
  76     /// ```
  77     pub USELESS_ATTRIBUTE,
  78     correctness,
  79     "use of lint attributes on `extern crate` items"
  80 }
  81
  82 declare_clippy_lint! {
  83     /// **What it does:** Checks for `#[deprecated]` annotations with a `since`
  84     /// field that is not a valid semantic version.
  85     ///
  86     /// **Why is this bad?** For checking the version of the deprecation, it must be
  87     /// a valid semver. Failing that, the contained information is useless.
  88     ///
  89     /// **Known problems:** None.
  90     ///
  91     /// **Example:**
  92     /// ```rust
  93     /// #[deprecated(since = "forever")]
  94     /// fn something_else() { /* ... */ }
  95     /// ```
  96     pub DEPRECATED_SEMVER,
  97     correctness,
  98     "use of `#[deprecated(since = \"x\")]` where x is not semver"
  99 }
 100
 101 declare_clippy_lint! {
 102     /// **What it does:** Checks for empty lines after outer attributes
 103     ///
 104     /// **Why is this bad?**
 105     /// Most likely the attribute was meant to be an inner attribute using a '!'.
 106     /// If it was meant to be an outer attribute, then the following item
 107     /// should not be separated by empty lines.
 108     ///
 109     /// **Known problems:** Can cause false positives.
 110     ///
 111     /// From the clippy side it's difficult to detect empty lines between an attributes and the
 112     /// following item because empty lines and comments are not part of the AST. The parsing
 113     /// currently works for basic cases but is not perfect.
 114     ///
 115     /// **Example:**
 116     /// ```rust
 117     /// // Good (as inner attribute)
 118     /// #![inline(always)]
 119     ///
 120     /// fn this_is_fine() { }
 121     ///
 122     /// // Bad
 123     /// #[inline(always)]
 124     ///
 125     /// fn not_quite_good_code() { }
 126     ///
 127     /// // Good (as outer attribute)
 128     /// #[inline(always)]
 129     /// fn this_is_fine_too() { }
 130     /// ```
 131     pub EMPTY_LINE_AFTER_OUTER_ATTR,
 132     nursery,
 133     "empty line after outer attribute"
 134 }
 135
 136 declare_clippy_lint! {
 137     /// **What it does:** Checks for `allow`/`warn`/`deny`/`forbid` attributes with scoped clippy
 138     /// lints and if those lints exist in clippy. If there is an uppercase letter in the lint name
 139     /// (not the tool name) and a lowercase version of this lint exists, it will suggest to lowercase
 140     /// the lint name.
 141     ///
 142     /// **Why is this bad?** A lint attribute with a mistyped lint name won't have an effect.
 143     ///
 144     /// **Known problems:** None.
 145     ///
 146     /// **Example:**
 147     /// Bad:
 148     /// ```rust
 149     /// #![warn(if_not_els)]
 150     /// #![deny(clippy::All)]
 151     /// ```
 152     ///
 153     /// Good:
 154     /// ```rust
 155     /// #![warn(if_not_else)]
 156     /// #![deny(clippy::all)]
 157     /// ```
 158     pub UNKNOWN_CLIPPY_LINTS,
 159     style,
 160     "unknown_lints for scoped Clippy lints"
 161 }
 162
 163 declare_clippy_lint! {
 164     /// **What it does:** Checks for `#[cfg_attr(rustfmt, rustfmt_skip)]` and suggests to replace it
 165     /// with `#[rustfmt::skip]`.
 166     ///
 167     /// **Why is this bad?** Since tool_attributes ([rust-lang/rust#44690](https://github.com/rust-lang/rust/issues/44690))
 168     /// are stable now, they should be used instead of the old `cfg_attr(rustfmt)` attributes.
 169     ///
 170     /// **Known problems:** This lint doesn't detect crate level inner attributes, because they get
 171     /// processed before the PreExpansionPass lints get executed. See
 172     /// [#3123](https://github.com/rust-lang/rust-clippy/pull/3123#issuecomment-422321765)
 173     ///
 174     /// **Example:**
 175     ///
 176     /// Bad:
 177     /// ```rust
 178     /// #[cfg_attr(rustfmt, rustfmt_skip)]
 179     /// fn main() { }
 180     /// ```
 181     ///
 182     /// Good:
 183     /// ```rust
 184     /// #[rustfmt::skip]
 185     /// fn main() { }
 186     /// ```
 187     pub DEPRECATED_CFG_ATTR,
 188     complexity,
 189     "usage of `cfg_attr(rustfmt)` instead of tool attributes"
 190 }
 191
 192 declare_lint_pass!(Attributes => [
 193     INLINE_ALWAYS,
 194     DEPRECATED_SEMVER,
 195     USELESS_ATTRIBUTE,
 196     EMPTY_LINE_AFTER_OUTER_ATTR,
 197     UNKNOWN_CLIPPY_LINTS,
 198 ]);
 199
 200 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Attributes {
 201     fn check_attribute(&mut self, cx: &LateContext<'a, 'tcx>, attr: &'tcx Attribute) {
 202         if let Some(items) = &attr.meta_item_list() {
 203             if let Some(ident) = attr.ident() {
 204                 match &*ident.as_str() {
 205                     "allow" | "warn" | "deny" | "forbid" => {
 206                         check_clippy_lint_names(cx, items);
 207                     },
 208                     _ => {},
 209                 }
 210                 if items.is_empty() || !attr.check_name(sym!(deprecated)) {
 211                     return;
 212                 }
 213                 for item in items {
 214                     if_chain! {
 215                         if let NestedMetaItem::MetaItem(mi) = &item;
 216                         if let MetaItemKind::NameValue(lit) = &mi.kind;
 217                         if mi.check_name(sym!(since));
 218                         then {
 219                             check_semver(cx, item.span(), lit);
 220                         }
 221                     }
 222                 }
 223             }
 224         }
 225     }
 226
 227     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item<'_>) {
 228         if is_relevant_item(cx, item) {
 229             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 230         }
 231         match item.kind {
 232             ItemKind::ExternCrate(..) | ItemKind::Use(..) => {
 233                 let skip_unused_imports = item.attrs.iter().any(|attr| attr.check_name(sym!(macro_use)));
 234
 235                 for attr in item.attrs {
 236                     if in_external_macro(cx.sess(), attr.span) {
 237                         return;
 238                     }
 239                     if let Some(lint_list) = &attr.meta_item_list() {
 240                         if let Some(ident) = attr.ident() {
 241                             match &*ident.as_str() {
 242                                 "allow" | "warn" | "deny" | "forbid" => {
 243                                     // whitelist `unused_imports`, `deprecated` and `unreachable_pub` for `use` items
 244                                     // and `unused_imports` for `extern crate` items with `macro_use`
 245                                     for lint in lint_list {
 246                                         match item.kind {
 247                                             ItemKind::Use(..) => {
 248                                                 if is_word(lint, sym!(unused_imports))
 249                                                     || is_word(lint, sym!(deprecated))
 250                                                     || is_word(lint, sym!(unreachable_pub))
 251                                                     || is_word(lint, sym!(unused))
 252                                                 {
 253                                                     return;
 254                                                 }
 255                                             },
 256                                             ItemKind::ExternCrate(..) => {
 257                                                 if is_word(lint, sym!(unused_imports)) && skip_unused_imports {
 258                                                     return;
 259                                                 }
 260                                                 if is_word(lint, sym!(unused_extern_crates)) {
 261                                                     return;
 262                                                 }
 263                                             },
 264                                             _ => {},
 265                                         }
 266                                     }
 267                                     let line_span = first_line_of_span(cx, attr.span);
 268
 269                                     if let Some(mut sugg) = snippet_opt(cx, line_span) {
 270                                         if sugg.contains("#[") {
 271                                             span_lint_and_then(
 272                                                 cx,
 273                                                 USELESS_ATTRIBUTE,
 274                                                 line_span,
 275                                                 "useless lint attribute",
 276                                                 |db| {
 277                                                     sugg = sugg.replacen("#[", "#![", 1);
 278                                                     db.span_suggestion(
 279                                                         line_span,
 280                                                         "if you just forgot a `!`, use",
 281                                                         sugg,
 282                                                         Applicability::MaybeIncorrect,
 283                                                     );
 284                                                 },
 285                                             );
 286                                         }
 287                                     }
 288                                 },
 289                                 _ => {},
 290                             }
 291                         }
 292                     }
 293                 }
 294             },
 295             _ => {},
 296         }
 297     }
 298
 299     fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem<'_>) {
 300         if is_relevant_impl(cx, item) {
 301             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 302         }
 303     }
 304
 305     fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem<'_>) {
 306         if is_relevant_trait(cx, item) {
 307             check_attrs(cx, item.span, item.ident.name, &item.attrs)
 308         }
 309     }
 310 }
 311
 312 #[allow(clippy::single_match_else)]
 313 fn check_clippy_lint_names(cx: &LateContext<'_, '_>, items: &[NestedMetaItem]) {
 314     let lint_store = cx.lints();
 315     for lint in items {
 316         if_chain! {
 317             if let Some(meta_item) = lint.meta_item();
 318             if meta_item.path.segments.len() > 1;
 319             if let tool_name = meta_item.path.segments[0].ident;
 320             if tool_name.as_str() == "clippy";
 321             let name = meta_item.path.segments.last().unwrap().ident.name;
 322             if let CheckLintNameResult::Tool(Err((None, _))) = lint_store.check_lint_name(
 323                 &name.as_str(),
 324                 Some(tool_name.name),
 325             );
 326             then {
 327                 span_lint_and_then(
 328                     cx,
 329                     UNKNOWN_CLIPPY_LINTS,
 330                     lint.span(),
 331                     &format!("unknown clippy lint: clippy::{}", name),
 332                     |db| {
 333                         let name_lower = name.as_str().to_lowercase();
 334                         let symbols = lint_store.get_lints().iter().map(
 335                             |l| Symbol::intern(&l.name_lower())
 336                         ).collect::<Vec<_>>();
 337                         let sugg = find_best_match_for_name(
 338                             symbols.iter(),
 339                             &format!("clippy::{}", name_lower),
 340                             None,
 341                         );
 342                         if name.as_str().chars().any(char::is_uppercase)
 343                             && lint_store.find_lints(&format!("clippy::{}", name_lower)).is_ok() {
 344                             db.span_suggestion(
 345                                 lint.span(),
 346                                 "lowercase the lint name",
 347                                 format!("clippy::{}", name_lower),
 348                                 Applicability::MachineApplicable,
 349                             );
 350                         } else if let Some(sugg) = sugg {
 351                             db.span_suggestion(
 352                                 lint.span(),
 353                                 "did you mean",
 354                                 sugg.to_string(),
 355                                 Applicability::MachineApplicable,
 356                             );
 357                         }
 358                     }
 359                 );
 360             }
 361         };
 362     }
 363 }
 364
 365 fn is_relevant_item(cx: &LateContext<'_, '_>, item: &Item<'_>) -> bool {
 366     if let ItemKind::Fn(_, _, eid) = item.kind {
 367         is_relevant_expr(cx, cx.tcx.body_tables(eid), &cx.tcx.hir().body(eid).value)
 368     } else {
 369         true
 370     }
 371 }
 372
 373 fn is_relevant_impl(cx: &LateContext<'_, '_>, item: &ImplItem<'_>) -> bool {
 374     match item.kind {
 375         ImplItemKind::Fn(_, eid) => is_relevant_expr(cx, cx.tcx.body_tables(eid), &cx.tcx.hir().body(eid).value),
 376         _ => false,
 377     }
 378 }
 379
 380 fn is_relevant_trait(cx: &LateContext<'_, '_>, item: &TraitItem<'_>) -> bool {
 381     match item.kind {
 382         TraitItemKind::Fn(_, TraitFn::Required(_)) => true,
 383         TraitItemKind::Fn(_, TraitFn::Provided(eid)) => {
 384             is_relevant_expr(cx, cx.tcx.body_tables(eid), &cx.tcx.hir().body(eid).value)
 385         },
 386         _ => false,
 387     }
 388 }
 389
 390 fn is_relevant_block(cx: &LateContext<'_, '_>, tables: &ty::TypeckTables<'_>, block: &Block<'_>) -> bool {
 391     if let Some(stmt) = block.stmts.first() {
 392         match &stmt.kind {
 393             StmtKind::Local(_) => true,
 394             StmtKind::Expr(expr) | StmtKind::Semi(expr) => is_relevant_expr(cx, tables, expr),
 395             _ => false,
 396         }
 397     } else {
 398         block.expr.as_ref().map_or(false, |e| is_relevant_expr(cx, tables, e))
 399     }
 400 }
 401
 402 fn is_relevant_expr(cx: &LateContext<'_, '_>, tables: &ty::TypeckTables<'_>, expr: &Expr<'_>) -> bool {
 403     match &expr.kind {
 404         ExprKind::Block(block, _) => is_relevant_block(cx, tables, block),
 405         ExprKind::Ret(Some(e)) => is_relevant_expr(cx, tables, e),
 406         ExprKind::Ret(None) | ExprKind::Break(_, None) => false,
 407         ExprKind::Call(path_expr, _) => {
 408             if let ExprKind::Path(qpath) = &path_expr.kind {
 409                 if let Some(fun_id) = tables.qpath_res(qpath, path_expr.hir_id).opt_def_id() {
 410                     !match_def_path(cx, fun_id, &paths::BEGIN_PANIC)
 411                 } else {
 412                     true
 413                 }
 414             } else {
 415                 true
 416             }
 417         },
 418         _ => true,
 419     }
 420 }
 421
 422 fn check_attrs(cx: &LateContext<'_, '_>, span: Span, name: Name, attrs: &[Attribute]) {
 423     if span.from_expansion() {
 424         return;
 425     }
 426
 427     for attr in attrs {
 428         let attr_item = if let AttrKind::Normal(ref attr) = attr.kind {
 429             attr
 430         } else {
 431             continue;
 432         };
 433
 434         if attr.style == AttrStyle::Outer {
 435             if attr_item.args.inner_tokens().is_empty() || !is_present_in_source(cx, attr.span) {
 436                 return;
 437             }
 438
 439             let begin_of_attr_to_item = Span::new(attr.span.lo(), span.lo(), span.ctxt());
 440             let end_of_attr_to_item = Span::new(attr.span.hi(), span.lo(), span.ctxt());
 441
 442             if let Some(snippet) = snippet_opt(cx, end_of_attr_to_item) {
 443                 let lines = snippet.split('\n').collect::<Vec<_>>();
 444                 let lines = without_block_comments(lines);
 445
 446                 if lines.iter().filter(|l| l.trim().is_empty()).count() > 2 {
 447                     span_lint(
 448                         cx,
 449                         EMPTY_LINE_AFTER_OUTER_ATTR,
 450                         begin_of_attr_to_item,
 451                         "Found an empty line after an outer attribute. \
 452                          Perhaps you forgot to add a `!` to make it an inner attribute?",
 453                     );
 454                 }
 455             }
 456         }
 457
 458         if let Some(values) = attr.meta_item_list() {
 459             if values.len() != 1 || !attr.check_name(sym!(inline)) {
 460                 continue;
 461             }
 462             if is_word(&values[0], sym!(always)) {
 463                 span_lint(
 464                     cx,
 465                     INLINE_ALWAYS,
 466                     attr.span,
 467                     &format!(
 468                         "you have declared `#[inline(always)]` on `{}`. This is usually a bad idea",
 469                         name
 470                     ),
 471                 );
 472             }
 473         }
 474     }
 475 }
 476
 477 fn check_semver(cx: &LateContext<'_, '_>, span: Span, lit: &Lit) {
 478     if let LitKind::Str(is, _) = lit.kind {
 479         if Version::parse(&is.as_str()).is_ok() {
 480             return;
 481         }
 482     }
 483     span_lint(
 484         cx,
 485         DEPRECATED_SEMVER,
 486         span,
 487         "the since field must contain a semver-compliant version",
 488     );
 489 }
 490
 491 fn is_word(nmi: &NestedMetaItem, expected: Symbol) -> bool {
 492     if let NestedMetaItem::MetaItem(mi) = &nmi {
 493         mi.is_word() && mi.check_name(expected)
 494     } else {
 495         false
 496     }
 497 }
 498
 499 declare_lint_pass!(DeprecatedCfgAttribute => [DEPRECATED_CFG_ATTR]);
 500
 501 impl EarlyLintPass for DeprecatedCfgAttribute {
 502     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &Attribute) {
 503         if_chain! {
 504             // check cfg_attr
 505             if attr.check_name(sym!(cfg_attr));
 506             if let Some(items) = attr.meta_item_list();
 507             if items.len() == 2;
 508             // check for `rustfmt`
 509             if let Some(feature_item) = items[0].meta_item();
 510             if feature_item.check_name(sym!(rustfmt));
 511             // check for `rustfmt_skip` and `rustfmt::skip`
 512             if let Some(skip_item) = &items[1].meta_item();
 513             if skip_item.check_name(sym!(rustfmt_skip)) ||
 514                 skip_item.path.segments.last().expect("empty path in attribute").ident.name == sym!(skip);
 515             // Only lint outer attributes, because custom inner attributes are unstable
 516             // Tracking issue: https://github.com/rust-lang/rust/issues/54726
 517             if let AttrStyle::Outer = attr.style;
 518             then {
 519                 span_lint_and_sugg(
 520                     cx,
 521                     DEPRECATED_CFG_ATTR,
 522                     attr.span,
 523                     "`cfg_attr` is deprecated for rustfmt and got replaced by tool attributes",
 524                     "use",
 525                     "#[rustfmt::skip]".to_string(),
 526                     Applicability::MachineApplicable,
 527                 );
 528             }
 529         }
 530     }
 531 }