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     /// // Bad
  63     /// fn foo(a: i32, _a: i32) {}
  64     ///
  65     /// // Good
  66     /// fn bar(a: i32, _b: i32) {}
  67     /// ```
  68     pub DUPLICATE_UNDERSCORE_ARGUMENT,
  69     style,
  70     "function arguments having names which only differ by an underscore"
  71 }
  72
  73 declare_clippy_lint! {
  74     /// **What it does:** Detects closures called in the same expression where they
  75     /// are defined.
  76     ///
  77     /// **Why is this bad?** It is unnecessarily adding to the expression's
  78     /// complexity.
  79     ///
  80     /// **Known problems:** None.
  81     ///
  82     /// **Example:**
  83     /// ```rust,ignore
  84     /// // Bad
  85     /// let a = (|| 42)()
  86     ///
  87     /// // Good
  88     /// let a = 42
  89     /// ```
  90     pub REDUNDANT_CLOSURE_CALL,
  91     complexity,
  92     "throwaway closures called in the expression they are defined"
  93 }
  94
  95 declare_clippy_lint! {
  96     /// **What it does:** Detects expressions of the form `--x`.
  97     ///
  98     /// **Why is this bad?** It can mislead C/C++ programmers to think `x` was
  99     /// decremented.
 100     ///
 101     /// **Known problems:** None.
 102     ///
 103     /// **Example:**
 104     /// ```rust
 105     /// let mut x = 3;
 106     /// --x;
 107     /// ```
 108     pub DOUBLE_NEG,
 109     style,
 110     "`--x`, which is a double negation of `x` and not a pre-decrement as in C/C++"
 111 }
 112
 113 declare_clippy_lint! {
 114     /// **What it does:** Warns on hexadecimal literals with mixed-case letter
 115     /// digits.
 116     ///
 117     /// **Why is this bad?** It looks confusing.
 118     ///
 119     /// **Known problems:** None.
 120     ///
 121     /// **Example:**
 122     /// ```rust
 123     /// // Bad
 124     /// let y = 0x1a9BAcD;
 125     ///
 126     /// // Good
 127     /// let y = 0x1A9BACD;
 128     /// ```
 129     pub MIXED_CASE_HEX_LITERALS,
 130     style,
 131     "hex literals whose letter digits are not consistently upper- or lowercased"
 132 }
 133
 134 declare_clippy_lint! {
 135     /// **What it does:** Warns if literal suffixes are not separated by an
 136     /// underscore.
 137     ///
 138     /// **Why is this bad?** It is much less readable.
 139     ///
 140     /// **Known problems:** None.
 141     ///
 142     /// **Example:**
 143     /// ```rust
 144     /// // Bad
 145     /// let y = 123832i32;
 146     ///
 147     /// // Good
 148     /// let y = 123832_i32;
 149     /// ```
 150     pub UNSEPARATED_LITERAL_SUFFIX,
 151     pedantic,
 152     "literals whose suffix is not separated by an underscore"
 153 }
 154
 155 declare_clippy_lint! {
 156     /// **What it does:** Warns if an integral constant literal starts with `0`.
 157     ///
 158     /// **Why is this bad?** In some languages (including the infamous C language
 159     /// and most of its
 160     /// family), this marks an octal constant. In Rust however, this is a decimal
 161     /// constant. This could
 162     /// be confusing for both the writer and a reader of the constant.
 163     ///
 164     /// **Known problems:** None.
 165     ///
 166     /// **Example:**
 167     ///
 168     /// In Rust:
 169     /// ```rust
 170     /// fn main() {
 171     ///     let a = 0123;
 172     ///     println!("{}", a);
 173     /// }
 174     /// ```
 175     ///
 176     /// prints `123`, while in C:
 177     ///
 178     /// ```c
 179     /// #include <stdio.h>
 180     ///
 181     /// int main() {
 182     ///     int a = 0123;
 183     ///     printf("%d\n", a);
 184     /// }
 185     /// ```
 186     ///
 187     /// prints `83` (as `83 == 0o123` while `123 == 0o173`).
 188     pub ZERO_PREFIXED_LITERAL,
 189     complexity,
 190     "integer literals starting with `0`"
 191 }
 192
 193 declare_clippy_lint! {
 194     /// **What it does:** Warns if a generic shadows a built-in type.
 195     ///
 196     /// **Why is this bad?** This gives surprising type errors.
 197     ///
 198     /// **Known problems:** None.
 199     ///
 200     /// **Example:**
 201     ///
 202     /// ```ignore
 203     /// impl<u32> Foo<u32> {
 204     ///     fn impl_func(&self) -> u32 {
 205     ///         42
 206     ///     }
 207     /// }
 208     /// ```
 209     pub BUILTIN_TYPE_SHADOW,
 210     style,
 211     "shadowing a builtin type"
 212 }
 213
 214 declare_clippy_lint! {
 215     /// **What it does:** Checks for patterns in the form `name @ _`.
 216     ///
 217     /// **Why is this bad?** It's almost always more readable to just use direct
 218     /// bindings.
 219     ///
 220     /// **Known problems:** None.
 221     ///
 222     /// **Example:**
 223     /// ```rust
 224     /// # let v = Some("abc");
 225     ///
 226     /// // Bad
 227     /// match v {
 228     ///     Some(x) => (),
 229     ///     y @ _ => (),
 230     /// }
 231     ///
 232     /// // Good
 233     /// match v {
 234     ///     Some(x) => (),
 235     ///     y => (),
 236     /// }
 237     /// ```
 238     pub REDUNDANT_PATTERN,
 239     style,
 240     "using `name @ _` in a pattern"
 241 }
 242
 243 declare_clippy_lint! {
 244     /// **What it does:** Checks for tuple patterns with a wildcard
 245     /// pattern (`_`) is next to a rest pattern (`..`).
 246     ///
 247     /// _NOTE_: While `_, ..` means there is at least one element left, `..`
 248     /// means there are 0 or more elements left. This can make a difference
 249     /// when refactoring, but shouldn't result in errors in the refactored code,
 250     /// since the wildcard pattern isn't used anyway.
 251     /// **Why is this bad?** The wildcard pattern is unneeded as the rest pattern
 252     /// can match that element as well.
 253     ///
 254     /// **Known problems:** None.
 255     ///
 256     /// **Example:**
 257     /// ```rust
 258     /// # struct TupleStruct(u32, u32, u32);
 259     /// # let t = TupleStruct(1, 2, 3);
 260     ///
 261     /// // Bad
 262     /// match t {
 263     ///     TupleStruct(0, .., _) => (),
 264     ///     _ => (),
 265     /// }
 266     ///
 267     /// // Good
 268     /// match t {
 269     ///     TupleStruct(0, ..) => (),
 270     ///     _ => (),
 271     /// }
 272     /// ```
 273     pub UNNEEDED_WILDCARD_PATTERN,
 274     complexity,
 275     "tuple patterns with a wildcard pattern (`_`) is next to a rest pattern (`..`)"
 276 }
 277
 278 declare_lint_pass!(MiscEarlyLints => [
 279     UNNEEDED_FIELD_PATTERN,
 280     DUPLICATE_UNDERSCORE_ARGUMENT,
 281     REDUNDANT_CLOSURE_CALL,
 282     DOUBLE_NEG,
 283     MIXED_CASE_HEX_LITERALS,
 284     UNSEPARATED_LITERAL_SUFFIX,
 285     ZERO_PREFIXED_LITERAL,
 286     BUILTIN_TYPE_SHADOW,
 287     REDUNDANT_PATTERN,
 288     UNNEEDED_WILDCARD_PATTERN,
 289 ]);
 290
 291 // Used to find `return` statements or equivalents e.g., `?`
 292 struct ReturnVisitor {
 293     found_return: bool,
 294 }
 295
 296 impl ReturnVisitor {
 297     #[must_use]
 298     fn new() -> Self {
 299         Self { found_return: false }
 300     }
 301 }
 302
 303 impl<'ast> Visitor<'ast> for ReturnVisitor {
 304     fn visit_expr(&mut self, ex: &'ast Expr) {
 305         if let ExprKind::Ret(_) = ex.kind {
 306             self.found_return = true;
 307         } else if let ExprKind::Try(_) = ex.kind {
 308             self.found_return = true;
 309         }
 310
 311         walk_expr(self, ex)
 312     }
 313 }
 314
 315 impl EarlyLintPass for MiscEarlyLints {
 316     fn check_generics(&mut self, cx: &EarlyContext<'_>, gen: &Generics) {
 317         for param in &gen.params {
 318             if let GenericParamKind::Type { .. } = param.kind {
 319                 let name = param.ident.as_str();
 320                 if constants::BUILTIN_TYPES.contains(&&*name) {
 321                     span_lint(
 322                         cx,
 323                         BUILTIN_TYPE_SHADOW,
 324                         param.ident.span,
 325                         &format!("This generic shadows the built-in type `{}`", name),
 326                     );
 327                 }
 328             }
 329         }
 330     }
 331
 332     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &Pat) {
 333         if let PatKind::Struct(ref npat, ref pfields, _) = pat.kind {
 334             let mut wilds = 0;
 335             let type_name = npat
 336                 .segments
 337                 .last()
 338                 .expect("A path must have at least one segment")
 339                 .ident
 340                 .name;
 341
 342             for field in pfields {
 343                 if let PatKind::Wild = field.pat.kind {
 344                     wilds += 1;
 345                 }
 346             }
 347             if !pfields.is_empty() && wilds == pfields.len() {
 348                 span_lint_and_help(
 349                     cx,
 350                     UNNEEDED_FIELD_PATTERN,
 351                     pat.span,
 352                     "All the struct fields are matched to a wildcard pattern, consider using `..`.",
 353                     None,
 354                     &format!("Try with `{} {{ .. }}` instead", type_name),
 355                 );
 356                 return;
 357             }
 358             if wilds > 0 {
 359                 for field in pfields {
 360                     if let PatKind::Wild = field.pat.kind {
 361                         wilds -= 1;
 362                         if wilds > 0 {
 363                             span_lint(
 364                                 cx,
 365                                 UNNEEDED_FIELD_PATTERN,
 366                                 field.span,
 367                                 "You matched a field with a wildcard pattern. Consider using `..` instead",
 368                             );
 369                         } else {
 370                             let mut normal = vec![];
 371
 372                             for field in pfields {
 373                                 match field.pat.kind {
 374                                     PatKind::Wild => {},
 375                                     _ => {
 376                                         if let Ok(n) = cx.sess().source_map().span_to_snippet(field.span) {
 377                                             normal.push(n);
 378                                         }
 379                                     },
 380                                 }
 381                             }
 382
 383                             span_lint_and_help(
 384                                 cx,
 385                                 UNNEEDED_FIELD_PATTERN,
 386                                 field.span,
 387                                 "You matched a field with a wildcard pattern. Consider using `..` \
 388                                  instead",
 389                                 None,
 390                                 &format!("Try with `{} {{ {}, .. }}`", type_name, normal[..].join(", ")),
 391                             );
 392                         }
 393                     }
 394                 }
 395             }
 396         }
 397
 398         if let PatKind::Ident(left, ident, Some(ref right)) = pat.kind {
 399             let left_binding = match left {
 400                 BindingMode::ByRef(Mutability::Mut) => "ref mut ",
 401                 BindingMode::ByRef(Mutability::Not) => "ref ",
 402                 BindingMode::ByValue(..) => "",
 403             };
 404
 405             if let PatKind::Wild = right.kind {
 406                 span_lint_and_sugg(
 407                     cx,
 408                     REDUNDANT_PATTERN,
 409                     pat.span,
 410                     &format!(
 411                         "the `{} @ _` pattern can be written as just `{}`",
 412                         ident.name, ident.name,
 413                     ),
 414                     "try",
 415                     format!("{}{}", left_binding, ident.name),
 416                     Applicability::MachineApplicable,
 417                 );
 418             }
 419         }
 420
 421         check_unneeded_wildcard_pattern(cx, pat);
 422     }
 423
 424     fn check_fn(&mut self, cx: &EarlyContext<'_>, fn_kind: FnKind<'_>, _: Span, _: NodeId) {
 425         let mut registered_names: FxHashMap<String, Span> = FxHashMap::default();
 426
 427         for arg in &fn_kind.decl().inputs {
 428             if let PatKind::Ident(_, ident, None) = arg.pat.kind {
 429                 let arg_name = ident.to_string();
 430
 431                 if arg_name.starts_with('_') {
 432                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 433                         span_lint(
 434                             cx,
 435                             DUPLICATE_UNDERSCORE_ARGUMENT,
 436                             *correspondence,
 437                             &format!(
 438                                 "`{}` already exists, having another argument having almost the same \
 439                                  name makes code comprehension and documentation more difficult",
 440                                 arg_name[1..].to_owned()
 441                             ),
 442                         );
 443                     }
 444                 } else {
 445                     registered_names.insert(arg_name, arg.pat.span);
 446                 }
 447             }
 448         }
 449     }
 450
 451     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 452         if in_external_macro(cx.sess(), expr.span) {
 453             return;
 454         }
 455         match expr.kind {
 456             ExprKind::Call(ref paren, _) => {
 457                 if let ExprKind::Paren(ref closure) = paren.kind {
 458                     if let ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.kind {
 459                         let mut visitor = ReturnVisitor::new();
 460                         visitor.visit_expr(block);
 461                         if !visitor.found_return {
 462                             span_lint_and_then(
 463                                 cx,
 464                                 REDUNDANT_CLOSURE_CALL,
 465                                 expr.span,
 466                                 "Try not to call a closure in the expression where it is declared.",
 467                                 |diag| {
 468                                     if decl.inputs.is_empty() {
 469                                         let mut app = Applicability::MachineApplicable;
 470                                         let hint =
 471                                             snippet_with_applicability(cx, block.span, "..", &mut app).into_owned();
 472                                         diag.span_suggestion(expr.span, "Try doing something like: ", hint, app);
 473                                     }
 474                                 },
 475                             );
 476                         }
 477                     }
 478                 }
 479             },
 480             ExprKind::Unary(UnOp::Neg, ref inner) => {
 481                 if let ExprKind::Unary(UnOp::Neg, _) = inner.kind {
 482                     span_lint(
 483                         cx,
 484                         DOUBLE_NEG,
 485                         expr.span,
 486                         "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 487                     );
 488                 }
 489             },
 490             ExprKind::Lit(ref lit) => Self::check_lit(cx, lit),
 491             _ => (),
 492         }
 493     }
 494
 495     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 496         for w in block.stmts.windows(2) {
 497             if_chain! {
 498                 if let StmtKind::Local(ref local) = w[0].kind;
 499                 if let Option::Some(ref t) = local.init;
 500                 if let ExprKind::Closure(..) = t.kind;
 501                 if let PatKind::Ident(_, ident, _) = local.pat.kind;
 502                 if let StmtKind::Semi(ref second) = w[1].kind;
 503                 if let ExprKind::Assign(_, ref call, _) = second.kind;
 504                 if let ExprKind::Call(ref closure, _) = call.kind;
 505                 if let ExprKind::Path(_, ref path) = closure.kind;
 506                 then {
 507                     if ident == path.segments[0].ident {
 508                         span_lint(
 509                             cx,
 510                             REDUNDANT_CLOSURE_CALL,
 511                             second.span,
 512                             "Closure called just once immediately after it was declared",
 513                         );
 514                     }
 515                 }
 516             }
 517         }
 518     }
 519 }
 520
 521 impl MiscEarlyLints {
 522     fn check_lit(cx: &EarlyContext<'_>, lit: &Lit) {
 523         // We test if first character in snippet is a number, because the snippet could be an expansion
 524         // from a built-in macro like `line!()` or a proc-macro like `#[wasm_bindgen]`.
 525         // Note that this check also covers special case that `line!()` is eagerly expanded by compiler.
 526         // See <https://github.com/rust-lang/rust-clippy/issues/4507> for a regression.
 527         // FIXME: Find a better way to detect those cases.
 528         let lit_snip = match snippet_opt(cx, lit.span) {
 529             Some(snip) if snip.chars().next().map_or(false, |c| c.is_digit(10)) => snip,
 530             _ => return,
 531         };
 532
 533         if let LitKind::Int(value, lit_int_type) = lit.kind {
 534             let suffix = match lit_int_type {
 535                 LitIntType::Signed(ty) => ty.name_str(),
 536                 LitIntType::Unsigned(ty) => ty.name_str(),
 537                 LitIntType::Unsuffixed => "",
 538             };
 539
 540             let maybe_last_sep_idx = if let Some(val) = lit_snip.len().checked_sub(suffix.len() + 1) {
 541                 val
 542             } else {
 543                 return; // It's useless so shouldn't lint.
 544             };
 545             // Do not lint when literal is unsuffixed.
 546             if !suffix.is_empty() && lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 547                 span_lint_and_sugg(
 548                     cx,
 549                     UNSEPARATED_LITERAL_SUFFIX,
 550                     lit.span,
 551                     "integer type suffix should be separated by an underscore",
 552                     "add an underscore",
 553                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 554                     Applicability::MachineApplicable,
 555                 );
 556             }
 557
 558             if lit_snip.starts_with("0x") {
 559                 if maybe_last_sep_idx <= 2 {
 560                     // It's meaningless or causes range error.
 561                     return;
 562                 }
 563                 let mut seen = (false, false);
 564                 for ch in lit_snip.as_bytes()[2..=maybe_last_sep_idx].iter() {
 565                     match ch {
 566                         b'a'..=b'f' => seen.0 = true,
 567                         b'A'..=b'F' => seen.1 = true,
 568                         _ => {},
 569                     }
 570                     if seen.0 && seen.1 {
 571                         span_lint(
 572                             cx,
 573                             MIXED_CASE_HEX_LITERALS,
 574                             lit.span,
 575                             "inconsistent casing in hexadecimal literal",
 576                         );
 577                         break;
 578                     }
 579                 }
 580             } else if lit_snip.starts_with("0b") || lit_snip.starts_with("0o") {
 581                 /* nothing to do */
 582             } else if value != 0 && lit_snip.starts_with('0') {
 583                 span_lint_and_then(
 584                     cx,
 585                     ZERO_PREFIXED_LITERAL,
 586                     lit.span,
 587                     "this is a decimal constant",
 588                     |diag| {
 589                         diag.span_suggestion(
 590                             lit.span,
 591                             "if you mean to use a decimal constant, remove the `0` to avoid confusion",
 592                             lit_snip.trim_start_matches(|c| c == '_' || c == '0').to_string(),
 593                             Applicability::MaybeIncorrect,
 594                         );
 595                         diag.span_suggestion(
 596                             lit.span,
 597                             "if you mean to use an octal constant, use `0o`",
 598                             format!("0o{}", lit_snip.trim_start_matches(|c| c == '_' || c == '0')),
 599                             Applicability::MaybeIncorrect,
 600                         );
 601                     },
 602                 );
 603             }
 604         } else if let LitKind::Float(_, LitFloatType::Suffixed(float_ty)) = lit.kind {
 605             let suffix = float_ty.name_str();
 606             let maybe_last_sep_idx = if let Some(val) = lit_snip.len().checked_sub(suffix.len() + 1) {
 607                 val
 608             } else {
 609                 return; // It's useless so shouldn't lint.
 610             };
 611             if lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 612                 span_lint_and_sugg(
 613                     cx,
 614                     UNSEPARATED_LITERAL_SUFFIX,
 615                     lit.span,
 616                     "float type suffix should be separated by an underscore",
 617                     "add an underscore",
 618                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 619                     Applicability::MachineApplicable,
 620                 );
 621             }
 622         }
 623     }
 624 }
 625
 626 fn check_unneeded_wildcard_pattern(cx: &EarlyContext<'_>, pat: &Pat) {
 627     if let PatKind::TupleStruct(_, ref patterns) | PatKind::Tuple(ref patterns) = pat.kind {
 628         fn span_lint(cx: &EarlyContext<'_>, span: Span, only_one: bool) {
 629             span_lint_and_sugg(
 630                 cx,
 631                 UNNEEDED_WILDCARD_PATTERN,
 632                 span,
 633                 if only_one {
 634                     "this pattern is unneeded as the `..` pattern can match that element"
 635                 } else {
 636                     "these patterns are unneeded as the `..` pattern can match those elements"
 637                 },
 638                 if only_one { "remove it" } else { "remove them" },
 639                 "".to_string(),
 640                 Applicability::MachineApplicable,
 641             );
 642         }
 643
 644         if let Some(rest_index) = patterns.iter().position(|pat| pat.is_rest()) {
 645             if let Some((left_index, left_pat)) = patterns[..rest_index]
 646                 .iter()
 647                 .rev()
 648                 .take_while(|pat| matches!(pat.kind, PatKind::Wild))
 649                 .enumerate()
 650                 .last()
 651             {
 652                 span_lint(cx, left_pat.span.until(patterns[rest_index].span), left_index == 0);
 653             }
 654
 655             if let Some((right_index, right_pat)) = patterns[rest_index + 1..]
 656                 .iter()
 657                 .take_while(|pat| matches!(pat.kind, PatKind::Wild))
 658                 .enumerate()
 659                 .last()
 660             {
 661                 span_lint(
 662                     cx,
 663                     patterns[rest_index].span.shrink_to_hi().to(right_pat.span),
 664                     right_index == 0,
 665                 );
 666             }
 667         }
 668     }
 669 }