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_lint_pass!(MiscEarlyLints => [
 199     UNNEEDED_FIELD_PATTERN,
 200     DUPLICATE_UNDERSCORE_ARGUMENT,
 201     REDUNDANT_CLOSURE_CALL,
 202     DOUBLE_NEG,
 203     MIXED_CASE_HEX_LITERALS,
 204     UNSEPARATED_LITERAL_SUFFIX,
 205     ZERO_PREFIXED_LITERAL,
 206     BUILTIN_TYPE_SHADOW,
 207     REDUNDANT_PATTERN
 208 ]);
 209
 210 // Used to find `return` statements or equivalents e.g., `?`
 211 struct ReturnVisitor {
 212     found_return: bool,
 213 }
 214
 215 impl ReturnVisitor {
 216     fn new() -> Self {
 217         Self { found_return: false }
 218     }
 219 }
 220
 221 impl<'ast> Visitor<'ast> for ReturnVisitor {
 222     fn visit_expr(&mut self, ex: &'ast Expr) {
 223         if let ExprKind::Ret(_) = ex.node {
 224             self.found_return = true;
 225         } else if let ExprKind::Try(_) = ex.node {
 226             self.found_return = true;
 227         }
 228
 229         walk_expr(self, ex)
 230     }
 231 }
 232
 233 impl EarlyLintPass for MiscEarlyLints {
 234     fn check_generics(&mut self, cx: &EarlyContext<'_>, gen: &Generics) {
 235         for param in &gen.params {
 236             if let GenericParamKind::Type { .. } = param.kind {
 237                 let name = param.ident.as_str();
 238                 if constants::BUILTIN_TYPES.contains(&&*name) {
 239                     span_lint(
 240                         cx,
 241                         BUILTIN_TYPE_SHADOW,
 242                         param.ident.span,
 243                         &format!("This generic shadows the built-in type `{}`", name),
 244                     );
 245                 }
 246             }
 247         }
 248     }
 249
 250     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &Pat) {
 251         if let PatKind::Struct(ref npat, ref pfields, _) = pat.node {
 252             let mut wilds = 0;
 253             let type_name = npat
 254                 .segments
 255                 .last()
 256                 .expect("A path must have at least one segment")
 257                 .ident
 258                 .name;
 259
 260             for field in pfields {
 261                 if let PatKind::Wild = field.pat.node {
 262                     wilds += 1;
 263                 }
 264             }
 265             if !pfields.is_empty() && wilds == pfields.len() {
 266                 span_help_and_lint(
 267                     cx,
 268                     UNNEEDED_FIELD_PATTERN,
 269                     pat.span,
 270                     "All the struct fields are matched to a wildcard pattern, consider using `..`.",
 271                     &format!("Try with `{} {{ .. }}` instead", type_name),
 272                 );
 273                 return;
 274             }
 275             if wilds > 0 {
 276                 let mut normal = vec![];
 277
 278                 for field in pfields {
 279                     match field.pat.node {
 280                         PatKind::Wild => {},
 281                         _ => {
 282                             if let Ok(n) = cx.sess().source_map().span_to_snippet(field.span) {
 283                                 normal.push(n);
 284                             }
 285                         },
 286                     }
 287                 }
 288                 for field in pfields {
 289                     if let PatKind::Wild = field.pat.node {
 290                         wilds -= 1;
 291                         if wilds > 0 {
 292                             span_lint(
 293                                 cx,
 294                                 UNNEEDED_FIELD_PATTERN,
 295                                 field.span,
 296                                 "You matched a field with a wildcard pattern. Consider using `..` instead",
 297                             );
 298                         } else {
 299                             span_help_and_lint(
 300                                 cx,
 301                                 UNNEEDED_FIELD_PATTERN,
 302                                 field.span,
 303                                 "You matched a field with a wildcard pattern. Consider using `..` \
 304                                  instead",
 305                                 &format!("Try with `{} {{ {}, .. }}`", type_name, normal[..].join(", ")),
 306                             );
 307                         }
 308                     }
 309                 }
 310             }
 311         }
 312
 313         if let PatKind::Ident(_, ident, Some(ref right)) = pat.node {
 314             if let PatKind::Wild = right.node {
 315                 span_lint_and_sugg(
 316                     cx,
 317                     REDUNDANT_PATTERN,
 318                     pat.span,
 319                     &format!(
 320                         "the `{} @ _` pattern can be written as just `{}`",
 321                         ident.name, ident.name,
 322                     ),
 323                     "try",
 324                     format!("{}", ident.name),
 325                     Applicability::MachineApplicable,
 326                 );
 327             }
 328         }
 329     }
 330
 331     fn check_fn(&mut self, cx: &EarlyContext<'_>, _: FnKind<'_>, decl: &FnDecl, _: Span, _: NodeId) {
 332         let mut registered_names: FxHashMap<String, Span> = FxHashMap::default();
 333
 334         for arg in &decl.inputs {
 335             if let PatKind::Ident(_, ident, None) = arg.pat.node {
 336                 let arg_name = ident.to_string();
 337
 338                 if arg_name.starts_with('_') {
 339                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 340                         span_lint(
 341                             cx,
 342                             DUPLICATE_UNDERSCORE_ARGUMENT,
 343                             *correspondence,
 344                             &format!(
 345                                 "`{}` already exists, having another argument having almost the same \
 346                                  name makes code comprehension and documentation more difficult",
 347                                 arg_name[1..].to_owned()
 348                             ),
 349                         );
 350                     }
 351                 } else {
 352                     registered_names.insert(arg_name, arg.pat.span);
 353                 }
 354             }
 355         }
 356     }
 357
 358     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 359         if in_external_macro(cx.sess(), expr.span) {
 360             return;
 361         }
 362         match expr.node {
 363             ExprKind::Call(ref paren, _) => {
 364                 if let ExprKind::Paren(ref closure) = paren.node {
 365                     if let ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.node {
 366                         let mut visitor = ReturnVisitor::new();
 367                         visitor.visit_expr(block);
 368                         if !visitor.found_return {
 369                             span_lint_and_then(
 370                                 cx,
 371                                 REDUNDANT_CLOSURE_CALL,
 372                                 expr.span,
 373                                 "Try not to call a closure in the expression where it is declared.",
 374                                 |db| {
 375                                     if decl.inputs.is_empty() {
 376                                         let hint = snippet(cx, block.span, "..").into_owned();
 377                                         db.span_suggestion(
 378                                             expr.span,
 379                                             "Try doing something like: ",
 380                                             hint,
 381                                             Applicability::MachineApplicable, // snippet
 382                                         );
 383                                     }
 384                                 },
 385                             );
 386                         }
 387                     }
 388                 }
 389             },
 390             ExprKind::Unary(UnOp::Neg, ref inner) => {
 391                 if let ExprKind::Unary(UnOp::Neg, _) = inner.node {
 392                     span_lint(
 393                         cx,
 394                         DOUBLE_NEG,
 395                         expr.span,
 396                         "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 397                     );
 398                 }
 399             },
 400             ExprKind::Lit(ref lit) => self.check_lit(cx, lit),
 401             _ => (),
 402         }
 403     }
 404
 405     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 406         for w in block.stmts.windows(2) {
 407             if_chain! {
 408                 if let StmtKind::Local(ref local) = w[0].node;
 409                 if let Option::Some(ref t) = local.init;
 410                 if let ExprKind::Closure(..) = t.node;
 411                 if let PatKind::Ident(_, ident, _) = local.pat.node;
 412                 if let StmtKind::Semi(ref second) = w[1].node;
 413                 if let ExprKind::Assign(_, ref call) = second.node;
 414                 if let ExprKind::Call(ref closure, _) = call.node;
 415                 if let ExprKind::Path(_, ref path) = closure.node;
 416                 then {
 417                     if ident == path.segments[0].ident {
 418                         span_lint(
 419                             cx,
 420                             REDUNDANT_CLOSURE_CALL,
 421                             second.span,
 422                             "Closure called just once immediately after it was declared",
 423                         );
 424                     }
 425                 }
 426             }
 427         }
 428     }
 429 }
 430
 431 impl MiscEarlyLints {
 432     fn check_lit(self, cx: &EarlyContext<'_>, lit: &Lit) {
 433         // We test if first character in snippet is a number, because the snippet could be an expansion
 434         // from a built-in macro like `line!()` or a proc-macro like `#[wasm_bindgen]`.
 435         // Note that this check also covers special case that `line!()` is eagerly expanded by compiler.
 436         // See <https://github.com/rust-lang/rust-clippy/issues/4507> for a regression.
 437         // FIXME: Find a better way to detect those cases.
 438         let lit_snip = match snippet_opt(cx, lit.span) {
 439             Some(snip) if snip.chars().next().map_or(false, |c| c.is_digit(10)) => snip,
 440             _ => return,
 441         };
 442
 443         if let LitKind::Int(value, lit_int_type) = lit.node {
 444             let suffix = match lit_int_type {
 445                 LitIntType::Signed(ty) => ty.ty_to_string(),
 446                 LitIntType::Unsigned(ty) => ty.ty_to_string(),
 447                 LitIntType::Unsuffixed => "",
 448             };
 449
 450             let maybe_last_sep_idx = lit_snip.len() - suffix.len() - 1;
 451             // Do not lint when literal is unsuffixed.
 452             if !suffix.is_empty() && lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 453                 span_lint_and_sugg(
 454                     cx,
 455                     UNSEPARATED_LITERAL_SUFFIX,
 456                     lit.span,
 457                     "integer type suffix should be separated by an underscore",
 458                     "add an underscore",
 459                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 460                     Applicability::MachineApplicable,
 461                 );
 462             }
 463
 464             if lit_snip.starts_with("0x") {
 465                 let mut seen = (false, false);
 466                 for ch in lit_snip.as_bytes()[2..=maybe_last_sep_idx].iter() {
 467                     match ch {
 468                         b'a'..=b'f' => seen.0 = true,
 469                         b'A'..=b'F' => seen.1 = true,
 470                         _ => {},
 471                     }
 472                     if seen.0 && seen.1 {
 473                         span_lint(
 474                             cx,
 475                             MIXED_CASE_HEX_LITERALS,
 476                             lit.span,
 477                             "inconsistent casing in hexadecimal literal",
 478                         );
 479                         break;
 480                     }
 481                 }
 482             } else if lit_snip.starts_with("0b") || lit_snip.starts_with("0o") {
 483                 /* nothing to do */
 484             } else if value != 0 && lit_snip.starts_with('0') {
 485                 span_lint_and_then(
 486                     cx,
 487                     ZERO_PREFIXED_LITERAL,
 488                     lit.span,
 489                     "this is a decimal constant",
 490                     |db| {
 491                         db.span_suggestion(
 492                             lit.span,
 493                             "if you mean to use a decimal constant, remove the `0` to avoid confusion",
 494                             lit_snip.trim_start_matches(|c| c == '_' || c == '0').to_string(),
 495                             Applicability::MaybeIncorrect,
 496                         );
 497                         db.span_suggestion(
 498                             lit.span,
 499                             "if you mean to use an octal constant, use `0o`",
 500                             format!("0o{}", lit_snip.trim_start_matches(|c| c == '_' || c == '0')),
 501                             Applicability::MaybeIncorrect,
 502                         );
 503                     },
 504                 );
 505             }
 506         } else if let LitKind::Float(_, float_ty) = lit.node {
 507             let suffix = float_ty.ty_to_string();
 508             let maybe_last_sep_idx = lit_snip.len() - suffix.len() - 1;
 509             if lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 510                 span_lint_and_sugg(
 511                     cx,
 512                     UNSEPARATED_LITERAL_SUFFIX,
 513                     lit.span,
 514                     "float type suffix should be separated by an underscore",
 515                     "add an underscore",
 516                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 517                     Applicability::MachineApplicable,
 518                 );
 519             }
 520         }
 521     }
 522 }