clippy_lints/src/misc_early.rs

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