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(
 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                 );
 324             }
 325         }
 326     }
 327
 328     fn check_fn(&mut self, cx: &EarlyContext<'_>, _: FnKind<'_>, decl: &FnDecl, _: Span, _: NodeId) {
 329         let mut registered_names: FxHashMap<String, Span> = FxHashMap::default();
 330
 331         for arg in &decl.inputs {
 332             if let PatKind::Ident(_, ident, None) = arg.pat.node {
 333                 let arg_name = ident.to_string();
 334
 335                 if arg_name.starts_with('_') {
 336                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 337                         span_lint(
 338                             cx,
 339                             DUPLICATE_UNDERSCORE_ARGUMENT,
 340                             *correspondence,
 341                             &format!(
 342                                 "`{}` already exists, having another argument having almost the same \
 343                                  name makes code comprehension and documentation more difficult",
 344                                 arg_name[1..].to_owned()
 345                             ),
 346                         );
 347                     }
 348                 } else {
 349                     registered_names.insert(arg_name, arg.pat.span);
 350                 }
 351             }
 352         }
 353     }
 354
 355     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 356         if in_external_macro(cx.sess(), expr.span) {
 357             return;
 358         }
 359         match expr.node {
 360             ExprKind::Call(ref paren, _) => {
 361                 if let ExprKind::Paren(ref closure) = paren.node {
 362                     if let ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.node {
 363                         let mut visitor = ReturnVisitor::new();
 364                         visitor.visit_expr(block);
 365                         if !visitor.found_return {
 366                             span_lint_and_then(
 367                                 cx,
 368                                 REDUNDANT_CLOSURE_CALL,
 369                                 expr.span,
 370                                 "Try not to call a closure in the expression where it is declared.",
 371                                 |db| {
 372                                     if decl.inputs.is_empty() {
 373                                         let hint = snippet(cx, block.span, "..").into_owned();
 374                                         db.span_suggestion(
 375                                             expr.span,
 376                                             "Try doing something like: ",
 377                                             hint,
 378                                             Applicability::MachineApplicable, // snippet
 379                                         );
 380                                     }
 381                                 },
 382                             );
 383                         }
 384                     }
 385                 }
 386             },
 387             ExprKind::Unary(UnOp::Neg, ref inner) => {
 388                 if let ExprKind::Unary(UnOp::Neg, _) = inner.node {
 389                     span_lint(
 390                         cx,
 391                         DOUBLE_NEG,
 392                         expr.span,
 393                         "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 394                     );
 395                 }
 396             },
 397             ExprKind::Lit(ref lit) => self.check_lit(cx, lit),
 398             _ => (),
 399         }
 400     }
 401
 402     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 403         for w in block.stmts.windows(2) {
 404             if_chain! {
 405                 if let StmtKind::Local(ref local) = w[0].node;
 406                 if let Option::Some(ref t) = local.init;
 407                 if let ExprKind::Closure(..) = t.node;
 408                 if let PatKind::Ident(_, ident, _) = local.pat.node;
 409                 if let StmtKind::Semi(ref second) = w[1].node;
 410                 if let ExprKind::Assign(_, ref call) = second.node;
 411                 if let ExprKind::Call(ref closure, _) = call.node;
 412                 if let ExprKind::Path(_, ref path) = closure.node;
 413                 then {
 414                     if ident == path.segments[0].ident {
 415                         span_lint(
 416                             cx,
 417                             REDUNDANT_CLOSURE_CALL,
 418                             second.span,
 419                             "Closure called just once immediately after it was declared",
 420                         );
 421                     }
 422                 }
 423             }
 424         }
 425     }
 426 }
 427
 428 impl MiscEarlyLints {
 429     fn check_lit(self, cx: &EarlyContext<'_>, lit: &Lit) {
 430         // The `line!()` macro is compiler built-in and a special case for these lints.
 431         let lit_snip = match snippet_opt(cx, lit.span) {
 432             Some(snip) => {
 433                 // The snip could be empty in case of expand from procedure macro
 434                 if snip.is_empty() || snip.contains('!') {
 435                     return;
 436                 }
 437                 snip
 438             },
 439             _ => return,
 440         };
 441
 442         if let LitKind::Int(value, lit_int_type) = lit.node {
 443             let suffix = match lit_int_type {
 444                 LitIntType::Signed(ty) => ty.ty_to_string(),
 445                 LitIntType::Unsigned(ty) => ty.ty_to_string(),
 446                 LitIntType::Unsuffixed => "",
 447             };
 448
 449             let maybe_last_sep_idx = lit_snip.len() - suffix.len() - 1;
 450             // Do not lint when literal is unsuffixed.
 451             if !suffix.is_empty() && lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 452                 span_lint_and_sugg(
 453                     cx,
 454                     UNSEPARATED_LITERAL_SUFFIX,
 455                     lit.span,
 456                     "integer type suffix should be separated by an underscore",
 457                     "add an underscore",
 458                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 459                     Applicability::MachineApplicable,
 460                 );
 461             }
 462
 463             if lit_snip.starts_with("0x") {
 464                 let mut seen = (false, false);
 465                 for ch in lit_snip.as_bytes()[2..=maybe_last_sep_idx].iter() {
 466                     match ch {
 467                         b'a'..=b'f' => seen.0 = true,
 468                         b'A'..=b'F' => seen.1 = true,
 469                         _ => {},
 470                     }
 471                     if seen.0 && seen.1 {
 472                         span_lint(
 473                             cx,
 474                             MIXED_CASE_HEX_LITERALS,
 475                             lit.span,
 476                             "inconsistent casing in hexadecimal literal",
 477                         );
 478                         break;
 479                     }
 480                 }
 481             } else if lit_snip.starts_with("0b") || lit_snip.starts_with("0o") {
 482                 /* nothing to do */
 483             } else if value != 0 && lit_snip.starts_with('0') {
 484                 span_lint_and_then(
 485                     cx,
 486                     ZERO_PREFIXED_LITERAL,
 487                     lit.span,
 488                     "this is a decimal constant",
 489                     |db| {
 490                         db.span_suggestion(
 491                             lit.span,
 492                             "if you mean to use a decimal constant, remove the `0` to avoid confusion",
 493                             lit_snip.trim_start_matches(|c| c == '_' || c == '0').to_string(),
 494                             Applicability::MaybeIncorrect,
 495                         );
 496                         db.span_suggestion(
 497                             lit.span,
 498                             "if you mean to use an octal constant, use `0o`",
 499                             format!("0o{}", lit_snip.trim_start_matches(|c| c == '_' || c == '0')),
 500                             Applicability::MaybeIncorrect,
 501                         );
 502                     },
 503                 );
 504             }
 505         } else if let LitKind::Float(_, float_ty) = lit.node {
 506             let suffix = float_ty.ty_to_string();
 507             let maybe_last_sep_idx = lit_snip.len() - suffix.len() - 1;
 508             if lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 509                 span_lint_and_sugg(
 510                     cx,
 511                     UNSEPARATED_LITERAL_SUFFIX,
 512                     lit.span,
 513                     "float type suffix should be separated by an underscore",
 514                     "add an underscore",
 515                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 516                     Applicability::MachineApplicable,
 517                 );
 518             }
 519         }
 520     }
 521 }