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