clippy_lints/src/misc_early.rs

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