clippy_lints/src/misc_early.rs

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