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::lint::in_external_macro;
   7 use rustc_ast::ast::{
   8     BindingMode, Block, Expr, ExprKind, GenericParamKind, Generics, Lit, LitFloatType, LitIntType, LitKind, Mutability,
   9     NodeId, Pat, PatKind, StmtKind, UnOp,
  10 };
  11 use rustc_ast::visit::{walk_expr, FnKind, Visitor};
  12 use rustc_data_structures::fx::FxHashMap;
  13 use rustc_errors::Applicability;
  14 use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
  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                 let mut normal = vec![];
 322
 323                 for field in pfields {
 324                     match field.pat.kind {
 325                         PatKind::Wild => {},
 326                         _ => {
 327                             if let Ok(n) = cx.sess().source_map().span_to_snippet(field.span) {
 328                                 normal.push(n);
 329                             }
 330                         },
 331                     }
 332                 }
 333                 for field in pfields {
 334                     if let PatKind::Wild = field.pat.kind {
 335                         wilds -= 1;
 336                         if wilds > 0 {
 337                             span_lint(
 338                                 cx,
 339                                 UNNEEDED_FIELD_PATTERN,
 340                                 field.span,
 341                                 "You matched a field with a wildcard pattern. Consider using `..` instead",
 342                             );
 343                         } else {
 344                             span_lint_and_help(
 345                                 cx,
 346                                 UNNEEDED_FIELD_PATTERN,
 347                                 field.span,
 348                                 "You matched a field with a wildcard pattern. Consider using `..` \
 349                                  instead",
 350                                 &format!("Try with `{} {{ {}, .. }}`", type_name, normal[..].join(", ")),
 351                             );
 352                         }
 353                     }
 354                 }
 355             }
 356         }
 357
 358         if let PatKind::Ident(left, ident, Some(ref right)) = pat.kind {
 359             let left_binding = match left {
 360                 BindingMode::ByRef(Mutability::Mut) => "ref mut ",
 361                 BindingMode::ByRef(Mutability::Not) => "ref ",
 362                 _ => "",
 363             };
 364
 365             if let PatKind::Wild = right.kind {
 366                 span_lint_and_sugg(
 367                     cx,
 368                     REDUNDANT_PATTERN,
 369                     pat.span,
 370                     &format!(
 371                         "the `{} @ _` pattern can be written as just `{}`",
 372                         ident.name, ident.name,
 373                     ),
 374                     "try",
 375                     format!("{}{}", left_binding, ident.name),
 376                     Applicability::MachineApplicable,
 377                 );
 378             }
 379         }
 380
 381         check_unneeded_wildcard_pattern(cx, pat);
 382     }
 383
 384     fn check_fn(&mut self, cx: &EarlyContext<'_>, fn_kind: FnKind<'_>, _: Span, _: NodeId) {
 385         let mut registered_names: FxHashMap<String, Span> = FxHashMap::default();
 386
 387         for arg in &fn_kind.decl().inputs {
 388             if let PatKind::Ident(_, ident, None) = arg.pat.kind {
 389                 let arg_name = ident.to_string();
 390
 391                 if arg_name.starts_with('_') {
 392                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 393                         span_lint(
 394                             cx,
 395                             DUPLICATE_UNDERSCORE_ARGUMENT,
 396                             *correspondence,
 397                             &format!(
 398                                 "`{}` already exists, having another argument having almost the same \
 399                                  name makes code comprehension and documentation more difficult",
 400                                 arg_name[1..].to_owned()
 401                             ),
 402                         );
 403                     }
 404                 } else {
 405                     registered_names.insert(arg_name, arg.pat.span);
 406                 }
 407             }
 408         }
 409     }
 410
 411     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 412         if in_external_macro(cx.sess(), expr.span) {
 413             return;
 414         }
 415         match expr.kind {
 416             ExprKind::Call(ref paren, _) => {
 417                 if let ExprKind::Paren(ref closure) = paren.kind {
 418                     if let ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.kind {
 419                         let mut visitor = ReturnVisitor::new();
 420                         visitor.visit_expr(block);
 421                         if !visitor.found_return {
 422                             span_lint_and_then(
 423                                 cx,
 424                                 REDUNDANT_CLOSURE_CALL,
 425                                 expr.span,
 426                                 "Try not to call a closure in the expression where it is declared.",
 427                                 |db| {
 428                                     if decl.inputs.is_empty() {
 429                                         let mut app = Applicability::MachineApplicable;
 430                                         let hint =
 431                                             snippet_with_applicability(cx, block.span, "..", &mut app).into_owned();
 432                                         db.span_suggestion(expr.span, "Try doing something like: ", hint, app);
 433                                     }
 434                                 },
 435                             );
 436                         }
 437                     }
 438                 }
 439             },
 440             ExprKind::Unary(UnOp::Neg, ref inner) => {
 441                 if let ExprKind::Unary(UnOp::Neg, _) = inner.kind {
 442                     span_lint(
 443                         cx,
 444                         DOUBLE_NEG,
 445                         expr.span,
 446                         "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 447                     );
 448                 }
 449             },
 450             ExprKind::Lit(ref lit) => Self::check_lit(cx, lit),
 451             _ => (),
 452         }
 453     }
 454
 455     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 456         for w in block.stmts.windows(2) {
 457             if_chain! {
 458                 if let StmtKind::Local(ref local) = w[0].kind;
 459                 if let Option::Some(ref t) = local.init;
 460                 if let ExprKind::Closure(..) = t.kind;
 461                 if let PatKind::Ident(_, ident, _) = local.pat.kind;
 462                 if let StmtKind::Semi(ref second) = w[1].kind;
 463                 if let ExprKind::Assign(_, ref call, _) = second.kind;
 464                 if let ExprKind::Call(ref closure, _) = call.kind;
 465                 if let ExprKind::Path(_, ref path) = closure.kind;
 466                 then {
 467                     if ident == path.segments[0].ident {
 468                         span_lint(
 469                             cx,
 470                             REDUNDANT_CLOSURE_CALL,
 471                             second.span,
 472                             "Closure called just once immediately after it was declared",
 473                         );
 474                     }
 475                 }
 476             }
 477         }
 478     }
 479 }
 480
 481 impl MiscEarlyLints {
 482     fn check_lit(cx: &EarlyContext<'_>, lit: &Lit) {
 483         // We test if first character in snippet is a number, because the snippet could be an expansion
 484         // from a built-in macro like `line!()` or a proc-macro like `#[wasm_bindgen]`.
 485         // Note that this check also covers special case that `line!()` is eagerly expanded by compiler.
 486         // See <https://github.com/rust-lang/rust-clippy/issues/4507> for a regression.
 487         // FIXME: Find a better way to detect those cases.
 488         let lit_snip = match snippet_opt(cx, lit.span) {
 489             Some(snip) if snip.chars().next().map_or(false, |c| c.is_digit(10)) => snip,
 490             _ => return,
 491         };
 492
 493         if let LitKind::Int(value, lit_int_type) = lit.kind {
 494             let suffix = match lit_int_type {
 495                 LitIntType::Signed(ty) => ty.name_str(),
 496                 LitIntType::Unsigned(ty) => ty.name_str(),
 497                 LitIntType::Unsuffixed => "",
 498             };
 499
 500             let maybe_last_sep_idx = if let Some(val) = lit_snip.len().checked_sub(suffix.len() + 1) {
 501                 val
 502             } else {
 503                 return; // It's useless so shouldn't lint.
 504             };
 505             // Do not lint when literal is unsuffixed.
 506             if !suffix.is_empty() && lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 507                 span_lint_and_sugg(
 508                     cx,
 509                     UNSEPARATED_LITERAL_SUFFIX,
 510                     lit.span,
 511                     "integer type suffix should be separated by an underscore",
 512                     "add an underscore",
 513                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 514                     Applicability::MachineApplicable,
 515                 );
 516             }
 517
 518             if lit_snip.starts_with("0x") {
 519                 if maybe_last_sep_idx <= 2 {
 520                     // It's meaningless or causes range error.
 521                     return;
 522                 }
 523                 let mut seen = (false, false);
 524                 for ch in lit_snip.as_bytes()[2..=maybe_last_sep_idx].iter() {
 525                     match ch {
 526                         b'a'..=b'f' => seen.0 = true,
 527                         b'A'..=b'F' => seen.1 = true,
 528                         _ => {},
 529                     }
 530                     if seen.0 && seen.1 {
 531                         span_lint(
 532                             cx,
 533                             MIXED_CASE_HEX_LITERALS,
 534                             lit.span,
 535                             "inconsistent casing in hexadecimal literal",
 536                         );
 537                         break;
 538                     }
 539                 }
 540             } else if lit_snip.starts_with("0b") || lit_snip.starts_with("0o") {
 541                 /* nothing to do */
 542             } else if value != 0 && lit_snip.starts_with('0') {
 543                 span_lint_and_then(
 544                     cx,
 545                     ZERO_PREFIXED_LITERAL,
 546                     lit.span,
 547                     "this is a decimal constant",
 548                     |db| {
 549                         db.span_suggestion(
 550                             lit.span,
 551                             "if you mean to use a decimal constant, remove the `0` to avoid confusion",
 552                             lit_snip.trim_start_matches(|c| c == '_' || c == '0').to_string(),
 553                             Applicability::MaybeIncorrect,
 554                         );
 555                         db.span_suggestion(
 556                             lit.span,
 557                             "if you mean to use an octal constant, use `0o`",
 558                             format!("0o{}", lit_snip.trim_start_matches(|c| c == '_' || c == '0')),
 559                             Applicability::MaybeIncorrect,
 560                         );
 561                     },
 562                 );
 563             }
 564         } else if let LitKind::Float(_, LitFloatType::Suffixed(float_ty)) = lit.kind {
 565             let suffix = float_ty.name_str();
 566             let maybe_last_sep_idx = if let Some(val) = lit_snip.len().checked_sub(suffix.len() + 1) {
 567                 val
 568             } else {
 569                 return; // It's useless so shouldn't lint.
 570             };
 571             if lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 572                 span_lint_and_sugg(
 573                     cx,
 574                     UNSEPARATED_LITERAL_SUFFIX,
 575                     lit.span,
 576                     "float type suffix should be separated by an underscore",
 577                     "add an underscore",
 578                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 579                     Applicability::MachineApplicable,
 580                 );
 581             }
 582         }
 583     }
 584 }
 585
 586 fn check_unneeded_wildcard_pattern(cx: &EarlyContext<'_>, pat: &Pat) {
 587     if let PatKind::TupleStruct(_, ref patterns) | PatKind::Tuple(ref patterns) = pat.kind {
 588         fn span_lint(cx: &EarlyContext<'_>, span: Span, only_one: bool) {
 589             span_lint_and_sugg(
 590                 cx,
 591                 UNNEEDED_WILDCARD_PATTERN,
 592                 span,
 593                 if only_one {
 594                     "this pattern is unneeded as the `..` pattern can match that element"
 595                 } else {
 596                     "these patterns are unneeded as the `..` pattern can match those elements"
 597                 },
 598                 if only_one { "remove it" } else { "remove them" },
 599                 "".to_string(),
 600                 Applicability::MachineApplicable,
 601             );
 602         }
 603
 604         #[allow(clippy::trivially_copy_pass_by_ref)]
 605         fn is_wild<P: std::ops::Deref<Target = Pat>>(pat: &&P) -> bool {
 606             if let PatKind::Wild = pat.kind {
 607                 true
 608             } else {
 609                 false
 610             }
 611         }
 612
 613         if let Some(rest_index) = patterns.iter().position(|pat| pat.is_rest()) {
 614             if let Some((left_index, left_pat)) = patterns[..rest_index]
 615                 .iter()
 616                 .rev()
 617                 .take_while(is_wild)
 618                 .enumerate()
 619                 .last()
 620             {
 621                 span_lint(cx, left_pat.span.until(patterns[rest_index].span), left_index == 0);
 622             }
 623
 624             if let Some((right_index, right_pat)) =
 625                 patterns[rest_index + 1..].iter().take_while(is_wild).enumerate().last()
 626             {
 627                 span_lint(
 628                     cx,
 629                     patterns[rest_index].span.shrink_to_hi().to(right_pat.span),
 630                     right_index == 0,
 631                 );
 632             }
 633         }
 634     }
 635 }