src/tools/clippy/clippy_lints/src/misc_early.rs

   1 use crate::utils::{
   2     constants, snippet_opt, snippet_with_applicability, span_lint, span_lint_and_help, span_lint_and_sugg,
   3     span_lint_and_then,
   4 };
   5 use if_chain::if_chain;
   6 use rustc_ast::ast::{
   7     BindingMode, Block, Expr, ExprKind, GenericParamKind, Generics, Lit, LitFloatType, LitIntType, LitKind, Mutability,
   8     NodeId, Pat, PatKind, StmtKind, UnOp,
   9 };
  10 use rustc_ast::visit::{walk_expr, FnKind, Visitor};
  11 use rustc_data_structures::fx::FxHashMap;
  12 use rustc_errors::Applicability;
  13 use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
  14 use rustc_middle::lint::in_external_macro;
  15 use rustc_session::{declare_lint_pass, declare_tool_lint};
  16 use rustc_span::source_map::Span;
  17
  18 declare_clippy_lint! {
  19     /// **What it does:** Checks for structure field patterns bound to wildcards.
  20     ///
  21     /// **Why is this bad?** Using `..` instead is shorter and leaves the focus on
  22     /// the fields that are actually bound.
  23     ///
  24     /// **Known problems:** None.
  25     ///
  26     /// **Example:**
  27     /// ```rust
  28     /// # struct Foo {
  29     /// #     a: i32,
  30     /// #     b: i32,
  31     /// #     c: i32,
  32     /// # }
  33     /// let f = Foo { a: 0, b: 0, c: 0 };
  34     ///
  35     /// // Bad
  36     /// match f {
  37     ///     Foo { a: _, b: 0, .. } => {},
  38     ///     Foo { a: _, b: _, c: _ } => {},
  39     /// }
  40     ///
  41     /// // Good
  42     /// match f {
  43     ///     Foo { b: 0, .. } => {},
  44     ///     Foo { .. } => {},
  45     /// }
  46     /// ```
  47     pub UNNEEDED_FIELD_PATTERN,
  48     restriction,
  49     "struct fields bound to a wildcard instead of using `..`"
  50 }
  51
  52 declare_clippy_lint! {
  53     /// **What it does:** Checks for function arguments having the similar names
  54     /// differing by an underscore.
  55     ///
  56     /// **Why is this bad?** It affects code readability.
  57     ///
  58     /// **Known problems:** None.
  59     ///
  60     /// **Example:**
  61     /// ```rust
  62     /// fn foo(a: i32, _a: i32) {}
  63     /// ```
  64     pub DUPLICATE_UNDERSCORE_ARGUMENT,
  65     style,
  66     "function arguments having names which only differ by an underscore"
  67 }
  68
  69 declare_clippy_lint! {
  70     /// **What it does:** Detects closures called in the same expression where they
  71     /// are defined.
  72     ///
  73     /// **Why is this bad?** It is unnecessarily adding to the expression's
  74     /// complexity.
  75     ///
  76     /// **Known problems:** None.
  77     ///
  78     /// **Example:**
  79     /// ```rust,ignore
  80     /// (|| 42)()
  81     /// ```
  82     pub REDUNDANT_CLOSURE_CALL,
  83     complexity,
  84     "throwaway closures called in the expression they are defined"
  85 }
  86
  87 declare_clippy_lint! {
  88     /// **What it does:** Detects expressions of the form `--x`.
  89     ///
  90     /// **Why is this bad?** It can mislead C/C++ programmers to think `x` was
  91     /// decremented.
  92     ///
  93     /// **Known problems:** None.
  94     ///
  95     /// **Example:**
  96     /// ```rust
  97     /// let mut x = 3;
  98     /// --x;
  99     /// ```
 100     pub DOUBLE_NEG,
 101     style,
 102     "`--x`, which is a double negation of `x` and not a pre-decrement as in C/C++"
 103 }
 104
 105 declare_clippy_lint! {
 106     /// **What it does:** Warns on hexadecimal literals with mixed-case letter
 107     /// digits.
 108     ///
 109     /// **Why is this bad?** It looks confusing.
 110     ///
 111     /// **Known problems:** None.
 112     ///
 113     /// **Example:**
 114     /// ```rust
 115     /// let y = 0x1a9BAcD;
 116     /// ```
 117     pub MIXED_CASE_HEX_LITERALS,
 118     style,
 119     "hex literals whose letter digits are not consistently upper- or lowercased"
 120 }
 121
 122 declare_clippy_lint! {
 123     /// **What it does:** Warns if literal suffixes are not separated by an
 124     /// underscore.
 125     ///
 126     /// **Why is this bad?** It is much less readable.
 127     ///
 128     /// **Known problems:** None.
 129     ///
 130     /// **Example:**
 131     /// ```rust
 132     /// let y = 123832i32;
 133     /// ```
 134     pub UNSEPARATED_LITERAL_SUFFIX,
 135     pedantic,
 136     "literals whose suffix is not separated by an underscore"
 137 }
 138
 139 declare_clippy_lint! {
 140     /// **What it does:** Warns if an integral constant literal starts with `0`.
 141     ///
 142     /// **Why is this bad?** In some languages (including the infamous C language
 143     /// and most of its
 144     /// family), this marks an octal constant. In Rust however, this is a decimal
 145     /// constant. This could
 146     /// be confusing for both the writer and a reader of the constant.
 147     ///
 148     /// **Known problems:** None.
 149     ///
 150     /// **Example:**
 151     ///
 152     /// In Rust:
 153     /// ```rust
 154     /// fn main() {
 155     ///     let a = 0123;
 156     ///     println!("{}", a);
 157     /// }
 158     /// ```
 159     ///
 160     /// prints `123`, while in C:
 161     ///
 162     /// ```c
 163     /// #include <stdio.h>
 164     ///
 165     /// int main() {
 166     ///     int a = 0123;
 167     ///     printf("%d\n", a);
 168     /// }
 169     /// ```
 170     ///
 171     /// prints `83` (as `83 == 0o123` while `123 == 0o173`).
 172     pub ZERO_PREFIXED_LITERAL,
 173     complexity,
 174     "integer literals starting with `0`"
 175 }
 176
 177 declare_clippy_lint! {
 178     /// **What it does:** Warns if a generic shadows a built-in type.
 179     ///
 180     /// **Why is this bad?** This gives surprising type errors.
 181     ///
 182     /// **Known problems:** None.
 183     ///
 184     /// **Example:**
 185     ///
 186     /// ```ignore
 187     /// impl<u32> Foo<u32> {
 188     ///     fn impl_func(&self) -> u32 {
 189     ///         42
 190     ///     }
 191     /// }
 192     /// ```
 193     pub BUILTIN_TYPE_SHADOW,
 194     style,
 195     "shadowing a builtin type"
 196 }
 197
 198 declare_clippy_lint! {
 199     /// **What it does:** Checks for patterns in the form `name @ _`.
 200     ///
 201     /// **Why is this bad?** It's almost always more readable to just use direct
 202     /// bindings.
 203     ///
 204     /// **Known problems:** None.
 205     ///
 206     /// **Example:**
 207     /// ```rust
 208     /// # let v = Some("abc");
 209     ///
 210     /// match v {
 211     ///     Some(x) => (),
 212     ///     y @ _ => (), // easier written as `y`,
 213     /// }
 214     /// ```
 215     pub REDUNDANT_PATTERN,
 216     style,
 217     "using `name @ _` in a pattern"
 218 }
 219
 220 declare_clippy_lint! {
 221     /// **What it does:** Checks for tuple patterns with a wildcard
 222     /// pattern (`_`) is next to a rest pattern (`..`).
 223     ///
 224     /// _NOTE_: While `_, ..` means there is at least one element left, `..`
 225     /// means there are 0 or more elements left. This can make a difference
 226     /// when refactoring, but shouldn't result in errors in the refactored code,
 227     /// since the wildcard pattern isn't used anyway.
 228     /// **Why is this bad?** The wildcard pattern is unneeded as the rest pattern
 229     /// can match that element as well.
 230     ///
 231     /// **Known problems:** None.
 232     ///
 233     /// **Example:**
 234     /// ```rust
 235     /// # struct TupleStruct(u32, u32, u32);
 236     /// # let t = TupleStruct(1, 2, 3);
 237     ///
 238     /// match t {
 239     ///     TupleStruct(0, .., _) => (),
 240     ///     _ => (),
 241     /// }
 242     /// ```
 243     /// can be written as
 244     /// ```rust
 245     /// # struct TupleStruct(u32, u32, u32);
 246     /// # let t = TupleStruct(1, 2, 3);
 247     ///
 248     /// match t {
 249     ///     TupleStruct(0, ..) => (),
 250     ///     _ => (),
 251     /// }
 252     /// ```
 253     pub UNNEEDED_WILDCARD_PATTERN,
 254     complexity,
 255     "tuple patterns with a wildcard pattern (`_`) is next to a rest pattern (`..`)"
 256 }
 257
 258 declare_lint_pass!(MiscEarlyLints => [
 259     UNNEEDED_FIELD_PATTERN,
 260     DUPLICATE_UNDERSCORE_ARGUMENT,
 261     REDUNDANT_CLOSURE_CALL,
 262     DOUBLE_NEG,
 263     MIXED_CASE_HEX_LITERALS,
 264     UNSEPARATED_LITERAL_SUFFIX,
 265     ZERO_PREFIXED_LITERAL,
 266     BUILTIN_TYPE_SHADOW,
 267     REDUNDANT_PATTERN,
 268     UNNEEDED_WILDCARD_PATTERN,
 269 ]);
 270
 271 // Used to find `return` statements or equivalents e.g., `?`
 272 struct ReturnVisitor {
 273     found_return: bool,
 274 }
 275
 276 impl ReturnVisitor {
 277     #[must_use]
 278     fn new() -> Self {
 279         Self { found_return: false }
 280     }
 281 }
 282
 283 impl<'ast> Visitor<'ast> for ReturnVisitor {
 284     fn visit_expr(&mut self, ex: &'ast Expr) {
 285         if let ExprKind::Ret(_) = ex.kind {
 286             self.found_return = true;
 287         } else if let ExprKind::Try(_) = ex.kind {
 288             self.found_return = true;
 289         }
 290
 291         walk_expr(self, ex)
 292     }
 293 }
 294
 295 impl EarlyLintPass for MiscEarlyLints {
 296     fn check_generics(&mut self, cx: &EarlyContext<'_>, gen: &Generics) {
 297         for param in &gen.params {
 298             if let GenericParamKind::Type { .. } = param.kind {
 299                 let name = param.ident.as_str();
 300                 if constants::BUILTIN_TYPES.contains(&&*name) {
 301                     span_lint(
 302                         cx,
 303                         BUILTIN_TYPE_SHADOW,
 304                         param.ident.span,
 305                         &format!("This generic shadows the built-in type `{}`", name),
 306                     );
 307                 }
 308             }
 309         }
 310     }
 311
 312     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &Pat) {
 313         if let PatKind::Struct(ref npat, ref pfields, _) = pat.kind {
 314             let mut wilds = 0;
 315             let type_name = npat
 316                 .segments
 317                 .last()
 318                 .expect("A path must have at least one segment")
 319                 .ident
 320                 .name;
 321
 322             for field in pfields {
 323                 if let PatKind::Wild = field.pat.kind {
 324                     wilds += 1;
 325                 }
 326             }
 327             if !pfields.is_empty() && wilds == pfields.len() {
 328                 span_lint_and_help(
 329                     cx,
 330                     UNNEEDED_FIELD_PATTERN,
 331                     pat.span,
 332                     "All the struct fields are matched to a wildcard pattern, consider using `..`.",
 333                     None,
 334                     &format!("Try with `{} {{ .. }}` instead", type_name),
 335                 );
 336                 return;
 337             }
 338             if wilds > 0 {
 339                 for field in pfields {
 340                     if let PatKind::Wild = field.pat.kind {
 341                         wilds -= 1;
 342                         if wilds > 0 {
 343                             span_lint(
 344                                 cx,
 345                                 UNNEEDED_FIELD_PATTERN,
 346                                 field.span,
 347                                 "You matched a field with a wildcard pattern. Consider using `..` instead",
 348                             );
 349                         } else {
 350                             let mut normal = vec![];
 351
 352                             for field in pfields {
 353                                 match field.pat.kind {
 354                                     PatKind::Wild => {},
 355                                     _ => {
 356                                         if let Ok(n) = cx.sess().source_map().span_to_snippet(field.span) {
 357                                             normal.push(n);
 358                                         }
 359                                     },
 360                                 }
 361                             }
 362
 363                             span_lint_and_help(
 364                                 cx,
 365                                 UNNEEDED_FIELD_PATTERN,
 366                                 field.span,
 367                                 "You matched a field with a wildcard pattern. Consider using `..` \
 368                                  instead",
 369                                 None,
 370                                 &format!("Try with `{} {{ {}, .. }}`", type_name, normal[..].join(", ")),
 371                             );
 372                         }
 373                     }
 374                 }
 375             }
 376         }
 377
 378         if let PatKind::Ident(left, ident, Some(ref right)) = pat.kind {
 379             let left_binding = match left {
 380                 BindingMode::ByRef(Mutability::Mut) => "ref mut ",
 381                 BindingMode::ByRef(Mutability::Not) => "ref ",
 382                 _ => "",
 383             };
 384
 385             if let PatKind::Wild = right.kind {
 386                 span_lint_and_sugg(
 387                     cx,
 388                     REDUNDANT_PATTERN,
 389                     pat.span,
 390                     &format!(
 391                         "the `{} @ _` pattern can be written as just `{}`",
 392                         ident.name, ident.name,
 393                     ),
 394                     "try",
 395                     format!("{}{}", left_binding, ident.name),
 396                     Applicability::MachineApplicable,
 397                 );
 398             }
 399         }
 400
 401         check_unneeded_wildcard_pattern(cx, pat);
 402     }
 403
 404     fn check_fn(&mut self, cx: &EarlyContext<'_>, fn_kind: FnKind<'_>, _: Span, _: NodeId) {
 405         let mut registered_names: FxHashMap<String, Span> = FxHashMap::default();
 406
 407         for arg in &fn_kind.decl().inputs {
 408             if let PatKind::Ident(_, ident, None) = arg.pat.kind {
 409                 let arg_name = ident.to_string();
 410
 411                 if arg_name.starts_with('_') {
 412                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 413                         span_lint(
 414                             cx,
 415                             DUPLICATE_UNDERSCORE_ARGUMENT,
 416                             *correspondence,
 417                             &format!(
 418                                 "`{}` already exists, having another argument having almost the same \
 419                                  name makes code comprehension and documentation more difficult",
 420                                 arg_name[1..].to_owned()
 421                             ),
 422                         );
 423                     }
 424                 } else {
 425                     registered_names.insert(arg_name, arg.pat.span);
 426                 }
 427             }
 428         }
 429     }
 430
 431     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 432         if in_external_macro(cx.sess(), expr.span) {
 433             return;
 434         }
 435         match expr.kind {
 436             ExprKind::Call(ref paren, _) => {
 437                 if let ExprKind::Paren(ref closure) = paren.kind {
 438                     if let ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.kind {
 439                         let mut visitor = ReturnVisitor::new();
 440                         visitor.visit_expr(block);
 441                         if !visitor.found_return {
 442                             span_lint_and_then(
 443                                 cx,
 444                                 REDUNDANT_CLOSURE_CALL,
 445                                 expr.span,
 446                                 "Try not to call a closure in the expression where it is declared.",
 447                                 |diag| {
 448                                     if decl.inputs.is_empty() {
 449                                         let mut app = Applicability::MachineApplicable;
 450                                         let hint =
 451                                             snippet_with_applicability(cx, block.span, "..", &mut app).into_owned();
 452                                         diag.span_suggestion(expr.span, "Try doing something like: ", hint, app);
 453                                     }
 454                                 },
 455                             );
 456                         }
 457                     }
 458                 }
 459             },
 460             ExprKind::Unary(UnOp::Neg, ref inner) => {
 461                 if let ExprKind::Unary(UnOp::Neg, _) = inner.kind {
 462                     span_lint(
 463                         cx,
 464                         DOUBLE_NEG,
 465                         expr.span,
 466                         "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 467                     );
 468                 }
 469             },
 470             ExprKind::Lit(ref lit) => Self::check_lit(cx, lit),
 471             _ => (),
 472         }
 473     }
 474
 475     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 476         for w in block.stmts.windows(2) {
 477             if_chain! {
 478                 if let StmtKind::Local(ref local) = w[0].kind;
 479                 if let Option::Some(ref t) = local.init;
 480                 if let ExprKind::Closure(..) = t.kind;
 481                 if let PatKind::Ident(_, ident, _) = local.pat.kind;
 482                 if let StmtKind::Semi(ref second) = w[1].kind;
 483                 if let ExprKind::Assign(_, ref call, _) = second.kind;
 484                 if let ExprKind::Call(ref closure, _) = call.kind;
 485                 if let ExprKind::Path(_, ref path) = closure.kind;
 486                 then {
 487                     if ident == path.segments[0].ident {
 488                         span_lint(
 489                             cx,
 490                             REDUNDANT_CLOSURE_CALL,
 491                             second.span,
 492                             "Closure called just once immediately after it was declared",
 493                         );
 494                     }
 495                 }
 496             }
 497         }
 498     }
 499 }
 500
 501 impl MiscEarlyLints {
 502     fn check_lit(cx: &EarlyContext<'_>, lit: &Lit) {
 503         // We test if first character in snippet is a number, because the snippet could be an expansion
 504         // from a built-in macro like `line!()` or a proc-macro like `#[wasm_bindgen]`.
 505         // Note that this check also covers special case that `line!()` is eagerly expanded by compiler.
 506         // See <https://github.com/rust-lang/rust-clippy/issues/4507> for a regression.
 507         // FIXME: Find a better way to detect those cases.
 508         let lit_snip = match snippet_opt(cx, lit.span) {
 509             Some(snip) if snip.chars().next().map_or(false, |c| c.is_digit(10)) => snip,
 510             _ => return,
 511         };
 512
 513         if let LitKind::Int(value, lit_int_type) = lit.kind {
 514             let suffix = match lit_int_type {
 515                 LitIntType::Signed(ty) => ty.name_str(),
 516                 LitIntType::Unsigned(ty) => ty.name_str(),
 517                 LitIntType::Unsuffixed => "",
 518             };
 519
 520             let maybe_last_sep_idx = if let Some(val) = lit_snip.len().checked_sub(suffix.len() + 1) {
 521                 val
 522             } else {
 523                 return; // It's useless so shouldn't lint.
 524             };
 525             // Do not lint when literal is unsuffixed.
 526             if !suffix.is_empty() && lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 527                 span_lint_and_sugg(
 528                     cx,
 529                     UNSEPARATED_LITERAL_SUFFIX,
 530                     lit.span,
 531                     "integer type suffix should be separated by an underscore",
 532                     "add an underscore",
 533                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 534                     Applicability::MachineApplicable,
 535                 );
 536             }
 537
 538             if lit_snip.starts_with("0x") {
 539                 if maybe_last_sep_idx <= 2 {
 540                     // It's meaningless or causes range error.
 541                     return;
 542                 }
 543                 let mut seen = (false, false);
 544                 for ch in lit_snip.as_bytes()[2..=maybe_last_sep_idx].iter() {
 545                     match ch {
 546                         b'a'..=b'f' => seen.0 = true,
 547                         b'A'..=b'F' => seen.1 = true,
 548                         _ => {},
 549                     }
 550                     if seen.0 && seen.1 {
 551                         span_lint(
 552                             cx,
 553                             MIXED_CASE_HEX_LITERALS,
 554                             lit.span,
 555                             "inconsistent casing in hexadecimal literal",
 556                         );
 557                         break;
 558                     }
 559                 }
 560             } else if lit_snip.starts_with("0b") || lit_snip.starts_with("0o") {
 561                 /* nothing to do */
 562             } else if value != 0 && lit_snip.starts_with('0') {
 563                 span_lint_and_then(
 564                     cx,
 565                     ZERO_PREFIXED_LITERAL,
 566                     lit.span,
 567                     "this is a decimal constant",
 568                     |diag| {
 569                         diag.span_suggestion(
 570                             lit.span,
 571                             "if you mean to use a decimal constant, remove the `0` to avoid confusion",
 572                             lit_snip.trim_start_matches(|c| c == '_' || c == '0').to_string(),
 573                             Applicability::MaybeIncorrect,
 574                         );
 575                         diag.span_suggestion(
 576                             lit.span,
 577                             "if you mean to use an octal constant, use `0o`",
 578                             format!("0o{}", lit_snip.trim_start_matches(|c| c == '_' || c == '0')),
 579                             Applicability::MaybeIncorrect,
 580                         );
 581                     },
 582                 );
 583             }
 584         } else if let LitKind::Float(_, LitFloatType::Suffixed(float_ty)) = lit.kind {
 585             let suffix = float_ty.name_str();
 586             let maybe_last_sep_idx = if let Some(val) = lit_snip.len().checked_sub(suffix.len() + 1) {
 587                 val
 588             } else {
 589                 return; // It's useless so shouldn't lint.
 590             };
 591             if lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 592                 span_lint_and_sugg(
 593                     cx,
 594                     UNSEPARATED_LITERAL_SUFFIX,
 595                     lit.span,
 596                     "float type suffix should be separated by an underscore",
 597                     "add an underscore",
 598                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 599                     Applicability::MachineApplicable,
 600                 );
 601             }
 602         }
 603     }
 604 }
 605
 606 fn check_unneeded_wildcard_pattern(cx: &EarlyContext<'_>, pat: &Pat) {
 607     if let PatKind::TupleStruct(_, ref patterns) | PatKind::Tuple(ref patterns) = pat.kind {
 608         fn span_lint(cx: &EarlyContext<'_>, span: Span, only_one: bool) {
 609             span_lint_and_sugg(
 610                 cx,
 611                 UNNEEDED_WILDCARD_PATTERN,
 612                 span,
 613                 if only_one {
 614                     "this pattern is unneeded as the `..` pattern can match that element"
 615                 } else {
 616                     "these patterns are unneeded as the `..` pattern can match those elements"
 617                 },
 618                 if only_one { "remove it" } else { "remove them" },
 619                 "".to_string(),
 620                 Applicability::MachineApplicable,
 621             );
 622         }
 623
 624         #[allow(clippy::trivially_copy_pass_by_ref)]
 625         fn is_wild<P: std::ops::Deref<Target = Pat>>(pat: &&P) -> bool {
 626             if let PatKind::Wild = pat.kind {
 627                 true
 628             } else {
 629                 false
 630             }
 631         }
 632
 633         if let Some(rest_index) = patterns.iter().position(|pat| pat.is_rest()) {
 634             if let Some((left_index, left_pat)) = patterns[..rest_index]
 635                 .iter()
 636                 .rev()
 637                 .take_while(is_wild)
 638                 .enumerate()
 639                 .last()
 640             {
 641                 span_lint(cx, left_pat.span.until(patterns[rest_index].span), left_index == 0);
 642             }
 643
 644             if let Some((right_index, right_pat)) =
 645                 patterns[rest_index + 1..].iter().take_while(is_wild).enumerate().last()
 646             {
 647                 span_lint(
 648                     cx,
 649                     patterns[rest_index].span.shrink_to_hi().to(right_pat.span),
 650                     right_index == 0,
 651                 );
 652             }
 653         }
 654     }
 655 }