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