clippy_lints/src/misc_early.rs

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