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, in_external_macro, snippet, snippet_opt, span_help_and_lint, span_lint, span_lint_and_then};
   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 param in &gen.params {
 192             if let GenericParam::Type(ref ty) = *param {
 193                 let name = ty.ident.name.as_str();
 194                 if constants::BUILTIN_TYPES.contains(&&*name) {
 195                     span_lint(
 196                         cx,
 197                         BUILTIN_TYPE_SHADOW,
 198                         ty.span,
 199                         &format!("This generic shadows the built-in type `{}`", name),
 200                     );
 201                 }
 202             }
 203         }
 204     }
 205
 206     fn check_pat(&mut self, cx: &EarlyContext, pat: &Pat) {
 207         if let PatKind::Struct(ref npat, ref pfields, _) = pat.node {
 208             let mut wilds = 0;
 209             let type_name = npat.segments
 210                 .last()
 211                 .expect("A path must have at least one segment")
 212                 .identifier
 213                 .name;
 214
 215             for field in pfields {
 216                 if field.node.pat.node == PatKind::Wild {
 217                     wilds += 1;
 218                 }
 219             }
 220             if !pfields.is_empty() && wilds == pfields.len() {
 221                 span_help_and_lint(
 222                     cx,
 223                     UNNEEDED_FIELD_PATTERN,
 224                     pat.span,
 225                     "All the struct fields are matched to a wildcard pattern, consider using `..`.",
 226                     &format!("Try with `{} {{ .. }}` instead", type_name),
 227                 );
 228                 return;
 229             }
 230             if wilds > 0 {
 231                 let mut normal = vec![];
 232
 233                 for field in pfields {
 234                     if field.node.pat.node != PatKind::Wild {
 235                         if let Ok(n) = cx.sess().codemap().span_to_snippet(field.span) {
 236                             normal.push(n);
 237                         }
 238                     }
 239                 }
 240                 for field in pfields {
 241                     if field.node.pat.node == PatKind::Wild {
 242                         wilds -= 1;
 243                         if wilds > 0 {
 244                             span_lint(
 245                                 cx,
 246                                 UNNEEDED_FIELD_PATTERN,
 247                                 field.span,
 248                                 "You matched a field with a wildcard pattern. Consider using `..` instead",
 249                             );
 250                         } else {
 251                             span_help_and_lint(
 252                                 cx,
 253                                 UNNEEDED_FIELD_PATTERN,
 254                                 field.span,
 255                                 "You matched a field with a wildcard pattern. Consider using `..` \
 256                                  instead",
 257                                 &format!("Try with `{} {{ {}, .. }}`", type_name, normal[..].join(", ")),
 258                             );
 259                         }
 260                     }
 261                 }
 262             }
 263         }
 264     }
 265
 266     fn check_fn(&mut self, cx: &EarlyContext, _: FnKind, decl: &FnDecl, _: Span, _: NodeId) {
 267         let mut registered_names: HashMap<String, Span> = HashMap::new();
 268
 269         for arg in &decl.inputs {
 270             if let PatKind::Ident(_, sp_ident, None) = arg.pat.node {
 271                 let arg_name = sp_ident.node.to_string();
 272
 273                 if arg_name.starts_with('_') {
 274                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 275                         span_lint(
 276                             cx,
 277                             DUPLICATE_UNDERSCORE_ARGUMENT,
 278                             *correspondence,
 279                             &format!(
 280                                 "`{}` already exists, having another argument having almost the same \
 281                                  name makes code comprehension and documentation more difficult",
 282                                 arg_name[1..].to_owned()
 283                             ),
 284                         );;
 285                     }
 286                 } else {
 287                     registered_names.insert(arg_name, arg.pat.span);
 288                 }
 289             }
 290         }
 291     }
 292
 293     fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
 294         if in_external_macro(cx, expr.span) {
 295             return;
 296         }
 297         match expr.node {
 298             ExprKind::Call(ref paren, _) => if let ExprKind::Paren(ref closure) = paren.node {
 299                 if let ExprKind::Closure(_, _, ref decl, ref block, _) = closure.node {
 300                     span_lint_and_then(
 301                         cx,
 302                         REDUNDANT_CLOSURE_CALL,
 303                         expr.span,
 304                         "Try not to call a closure in the expression where it is declared.",
 305                         |db| if decl.inputs.is_empty() {
 306                             let hint = snippet(cx, block.span, "..").into_owned();
 307                             db.span_suggestion(expr.span, "Try doing something like: ", hint);
 308                         },
 309                     );
 310                 }
 311             },
 312             ExprKind::Unary(UnOp::Neg, ref inner) => if let ExprKind::Unary(UnOp::Neg, _) = inner.node {
 313                 span_lint(
 314                     cx,
 315                     DOUBLE_NEG,
 316                     expr.span,
 317                     "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 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_chain! {
 328                 if let StmtKind::Local(ref local) = w[0].node;
 329                 if let Option::Some(ref t) = local.init;
 330                 if let ExprKind::Closure(_, _, _, _, _) = t.node;
 331                 if let PatKind::Ident(_, sp_ident, _) = local.pat.node;
 332                 if let StmtKind::Semi(ref second) = w[1].node;
 333                 if let ExprKind::Assign(_, ref call) = second.node;
 334                 if let ExprKind::Call(ref closure, _) = call.node;
 335                 if let ExprKind::Path(_, ref path) = closure.node;
 336                 then {
 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
 351 impl MiscEarly {
 352     fn check_lit(&self, cx: &EarlyContext, lit: &Lit) {
 353         if_chain! {
 354             if let LitKind::Int(value, ..) = lit.node;
 355             if let Some(src) = snippet_opt(cx, lit.span);
 356             if let Some(firstch) = src.chars().next();
 357             if char::to_digit(firstch, 10).is_some();
 358             then {
 359                 let mut prev = '\0';
 360                 for ch in src.chars() {
 361                     if ch == 'i' || ch == 'u' {
 362                         if prev != '_' {
 363                             span_lint(cx, UNSEPARATED_LITERAL_SUFFIX, lit.span,
 364                                         "integer type suffix should be separated by an underscore");
 365                         }
 366                         break;
 367                     }
 368                     prev = ch;
 369                 }
 370                 if src.starts_with("0x") {
 371                     let mut seen = (false, false);
 372                     for ch in src.chars() {
 373                         match ch {
 374                             'a' ... 'f' => seen.0 = true,
 375                             'A' ... 'F' => seen.1 = true,
 376                             'i' | 'u'   => break,   // start of suffix already
 377                             _ => ()
 378                         }
 379                     }
 380                     if seen.0 && seen.1 {
 381                         span_lint(cx, MIXED_CASE_HEX_LITERALS, lit.span,
 382                                     "inconsistent casing in hexadecimal literal");
 383                     }
 384                 } else if src.starts_with("0b") || src.starts_with("0o") {
 385                     /* nothing to do */
 386                 } else if value != 0 && src.starts_with('0') {
 387                     span_lint_and_then(cx,
 388                                         ZERO_PREFIXED_LITERAL,
 389                                         lit.span,
 390                                         "this is a decimal constant",
 391                                         |db| {
 392                         db.span_suggestion(
 393                             lit.span,
 394                             "if you mean to use a decimal constant, remove the `0` to remove confusion",
 395                             src.trim_left_matches(|c| c == '_' || c == '0').to_string(),
 396                         );
 397                         db.span_suggestion(
 398                             lit.span,
 399                             "if you mean to use an octal constant, use `0o`",
 400                             format!("0o{}", src.trim_left_matches(|c| c == '_' || c == '0')),
 401                         );
 402                     });
 403                 }
 404             }
 405         }
 406         if_chain! {
 407             if let LitKind::Float(..) = lit.node;
 408             if let Some(src) = snippet_opt(cx, lit.span);
 409             if let Some(firstch) = src.chars().next();
 410             if char::to_digit(firstch, 10).is_some();
 411             then {
 412                 let mut prev = '\0';
 413                 for ch in src.chars() {
 414                     if ch == 'f' {
 415                         if prev != '_' {
 416                             span_lint(cx, UNSEPARATED_LITERAL_SUFFIX, lit.span,
 417                                         "float type suffix should be separated by an underscore");
 418                         }
 419                         break;
 420                     }
 421                     prev = ch;
 422                 }
 423             }
 424         }
 425     }
 426 }