clippy_lints/src/misc_early.rs

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