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