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