clippy_lints/src/misc_early.rs

   1 use crate::utils::{constants, snippet, snippet_opt, span_help_and_lint, span_lint, span_lint_and_then};
   2 use if_chain::if_chain;
   3 use rustc::lint::{in_external_macro, EarlyContext, EarlyLintPass, LintArray, LintContext, LintPass};
   4 use rustc::{declare_tool_lint, lint_array};
   5 use rustc_data_structures::fx::FxHashMap;
   6 use rustc_errors::Applicability;
   7 use std::char;
   8 use syntax::ast::*;
   9 use syntax::source_map::Span;
  10 use syntax::visit::{walk_expr, FnKind, Visitor};
  11
  12 declare_clippy_lint! {
  13     /// **What it does:** Checks for structure field patterns bound to wildcards.
  14     ///
  15     /// **Why is this bad?** Using `..` instead is shorter and leaves the focus on
  16     /// the fields that are actually bound.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```rust
  22     /// let { a: _, b: ref b, c: _ } = ..
  23     /// ```
  24     pub UNNEEDED_FIELD_PATTERN,
  25     style,
  26     "struct fields bound to a wildcard instead of using `..`"
  27 }
  28
  29 declare_clippy_lint! {
  30     /// **What it does:** Checks for function arguments having the similar names
  31     /// differing by an underscore.
  32     ///
  33     /// **Why is this bad?** It affects code readability.
  34     ///
  35     /// **Known problems:** None.
  36     ///
  37     /// **Example:**
  38     /// ```rust
  39     /// fn foo(a: i32, _a: i32) {}
  40     /// ```
  41     pub DUPLICATE_UNDERSCORE_ARGUMENT,
  42     style,
  43     "function arguments having names which only differ by an underscore"
  44 }
  45
  46 declare_clippy_lint! {
  47     /// **What it does:** Detects closures called in the same expression where they
  48     /// are defined.
  49     ///
  50     /// **Why is this bad?** It is unnecessarily adding to the expression's
  51     /// complexity.
  52     ///
  53     /// **Known problems:** None.
  54     ///
  55     /// **Example:**
  56     /// ```rust
  57     /// (|| 42)()
  58     /// ```
  59     pub REDUNDANT_CLOSURE_CALL,
  60     complexity,
  61     "throwaway closures called in the expression they are defined"
  62 }
  63
  64 declare_clippy_lint! {
  65     /// **What it does:** Detects expressions of the form `--x`.
  66     ///
  67     /// **Why is this bad?** It can mislead C/C++ programmers to think `x` was
  68     /// decremented.
  69     ///
  70     /// **Known problems:** None.
  71     ///
  72     /// **Example:**
  73     /// ```rust
  74     /// --x;
  75     /// ```
  76     pub DOUBLE_NEG,
  77     style,
  78     "`--x`, which is a double negation of `x` and not a pre-decrement as in C/C++"
  79 }
  80
  81 declare_clippy_lint! {
  82     /// **What it does:** Warns on hexadecimal literals with mixed-case letter
  83     /// digits.
  84     ///
  85     /// **Why is this bad?** It looks confusing.
  86     ///
  87     /// **Known problems:** None.
  88     ///
  89     /// **Example:**
  90     /// ```rust
  91     /// let y = 0x1a9BAcD;
  92     /// ```
  93     pub MIXED_CASE_HEX_LITERALS,
  94     style,
  95     "hex literals whose letter digits are not consistently upper- or lowercased"
  96 }
  97
  98 declare_clippy_lint! {
  99     /// **What it does:** Warns if literal suffixes are not separated by an
 100     /// underscore.
 101     ///
 102     /// **Why is this bad?** It is much less readable.
 103     ///
 104     /// **Known problems:** None.
 105     ///
 106     /// **Example:**
 107     /// ```rust
 108     /// let y = 123832i32;
 109     /// ```
 110     pub UNSEPARATED_LITERAL_SUFFIX,
 111     pedantic,
 112     "literals whose suffix is not separated by an underscore"
 113 }
 114
 115 declare_clippy_lint! {
 116     /// **What it does:** Warns if an integral constant literal starts with `0`.
 117     ///
 118     /// **Why is this bad?** In some languages (including the infamous C language
 119     /// and most of its
 120     /// family), this marks an octal constant. In Rust however, this is a decimal
 121     /// constant. This could
 122     /// be confusing for both the writer and a reader of the constant.
 123     ///
 124     /// **Known problems:** None.
 125     ///
 126     /// **Example:**
 127     ///
 128     /// In Rust:
 129     /// ```rust
 130     /// fn main() {
 131     ///     let a = 0123;
 132     ///     println!("{}", a);
 133     /// }
 134     /// ```
 135     ///
 136     /// prints `123`, while in C:
 137     ///
 138     /// ```c
 139     /// #include <stdio.h>
 140     ///
 141     /// int main() {
 142     ///     int a = 0123;
 143     ///     printf("%d\n", a);
 144     /// }
 145     /// ```
 146     ///
 147     /// prints `83` (as `83 == 0o123` while `123 == 0o173`).
 148     pub ZERO_PREFIXED_LITERAL,
 149     complexity,
 150     "integer literals starting with `0`"
 151 }
 152
 153 declare_clippy_lint! {
 154     /// **What it does:** Warns if a generic shadows a built-in type.
 155     ///
 156     /// **Why is this bad?** This gives surprising type errors.
 157     ///
 158     /// **Known problems:** None.
 159     ///
 160     /// **Example:**
 161     ///
 162     /// ```rust
 163     /// impl<u32> Foo<u32> {
 164     ///     fn impl_func(&self) -> u32 {
 165     ///         42
 166     ///     }
 167     /// }
 168     /// ```
 169     pub BUILTIN_TYPE_SHADOW,
 170     style,
 171     "shadowing a builtin type"
 172 }
 173
 174 #[derive(Copy, Clone)]
 175 pub struct MiscEarly;
 176
 177 impl LintPass for MiscEarly {
 178     fn get_lints(&self) -> LintArray {
 179         lint_array!(
 180             UNNEEDED_FIELD_PATTERN,
 181             DUPLICATE_UNDERSCORE_ARGUMENT,
 182             REDUNDANT_CLOSURE_CALL,
 183             DOUBLE_NEG,
 184             MIXED_CASE_HEX_LITERALS,
 185             UNSEPARATED_LITERAL_SUFFIX,
 186             ZERO_PREFIXED_LITERAL,
 187             BUILTIN_TYPE_SHADOW
 188         )
 189     }
 190
 191     fn name(&self) -> &'static str {
 192         "MiscEarlyLints"
 193     }
 194 }
 195
 196 // Used to find `return` statements or equivalents e.g. `?`
 197 struct ReturnVisitor {
 198     found_return: bool,
 199 }
 200
 201 impl ReturnVisitor {
 202     fn new() -> Self {
 203         Self { found_return: false }
 204     }
 205 }
 206
 207 impl<'ast> Visitor<'ast> for ReturnVisitor {
 208     fn visit_expr(&mut self, ex: &'ast Expr) {
 209         if let ExprKind::Ret(_) = ex.node {
 210             self.found_return = true;
 211         } else if let ExprKind::Try(_) = ex.node {
 212             self.found_return = true;
 213         }
 214
 215         walk_expr(self, ex)
 216     }
 217 }
 218
 219 impl EarlyLintPass for MiscEarly {
 220     fn check_generics(&mut self, cx: &EarlyContext<'_>, gen: &Generics) {
 221         for param in &gen.params {
 222             if let GenericParamKind::Type { .. } = param.kind {
 223                 let name = param.ident.as_str();
 224                 if constants::BUILTIN_TYPES.contains(&&*name) {
 225                     span_lint(
 226                         cx,
 227                         BUILTIN_TYPE_SHADOW,
 228                         param.ident.span,
 229                         &format!("This generic shadows the built-in type `{}`", name),
 230                     );
 231                 }
 232             }
 233         }
 234     }
 235
 236     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &Pat, _: &mut bool) {
 237         if let PatKind::Struct(ref npat, ref pfields, _) = pat.node {
 238             let mut wilds = 0;
 239             let type_name = npat
 240                 .segments
 241                 .last()
 242                 .expect("A path must have at least one segment")
 243                 .ident
 244                 .name;
 245
 246             for field in pfields {
 247                 if let PatKind::Wild = field.node.pat.node {
 248                     wilds += 1;
 249                 }
 250             }
 251             if !pfields.is_empty() && wilds == pfields.len() {
 252                 span_help_and_lint(
 253                     cx,
 254                     UNNEEDED_FIELD_PATTERN,
 255                     pat.span,
 256                     "All the struct fields are matched to a wildcard pattern, consider using `..`.",
 257                     &format!("Try with `{} {{ .. }}` instead", type_name),
 258                 );
 259                 return;
 260             }
 261             if wilds > 0 {
 262                 let mut normal = vec![];
 263
 264                 for field in pfields {
 265                     match field.node.pat.node {
 266                         PatKind::Wild => {},
 267                         _ => {
 268                             if let Ok(n) = cx.sess().source_map().span_to_snippet(field.span) {
 269                                 normal.push(n);
 270                             }
 271                         },
 272                     }
 273                 }
 274                 for field in pfields {
 275                     if let PatKind::Wild = field.node.pat.node {
 276                         wilds -= 1;
 277                         if wilds > 0 {
 278                             span_lint(
 279                                 cx,
 280                                 UNNEEDED_FIELD_PATTERN,
 281                                 field.span,
 282                                 "You matched a field with a wildcard pattern. Consider using `..` instead",
 283                             );
 284                         } else {
 285                             span_help_and_lint(
 286                                 cx,
 287                                 UNNEEDED_FIELD_PATTERN,
 288                                 field.span,
 289                                 "You matched a field with a wildcard pattern. Consider using `..` \
 290                                  instead",
 291                                 &format!("Try with `{} {{ {}, .. }}`", type_name, normal[..].join(", ")),
 292                             );
 293                         }
 294                     }
 295                 }
 296             }
 297         }
 298     }
 299
 300     fn check_fn(&mut self, cx: &EarlyContext<'_>, _: FnKind<'_>, decl: &FnDecl, _: Span, _: NodeId) {
 301         let mut registered_names: FxHashMap<String, Span> = FxHashMap::default();
 302
 303         for arg in &decl.inputs {
 304             if let PatKind::Ident(_, ident, None) = arg.pat.node {
 305                 let arg_name = ident.to_string();
 306
 307                 if arg_name.starts_with('_') {
 308                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 309                         span_lint(
 310                             cx,
 311                             DUPLICATE_UNDERSCORE_ARGUMENT,
 312                             *correspondence,
 313                             &format!(
 314                                 "`{}` already exists, having another argument having almost the same \
 315                                  name makes code comprehension and documentation more difficult",
 316                                 arg_name[1..].to_owned()
 317                             ),
 318                         );;
 319                     }
 320                 } else {
 321                     registered_names.insert(arg_name, arg.pat.span);
 322                 }
 323             }
 324         }
 325     }
 326
 327     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 328         if in_external_macro(cx.sess(), expr.span) {
 329             return;
 330         }
 331         match expr.node {
 332             ExprKind::Call(ref paren, _) => {
 333                 if let ExprKind::Paren(ref closure) = paren.node {
 334                     if let ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.node {
 335                         let mut visitor = ReturnVisitor::new();
 336                         visitor.visit_expr(block);
 337                         if !visitor.found_return {
 338                             span_lint_and_then(
 339                                 cx,
 340                                 REDUNDANT_CLOSURE_CALL,
 341                                 expr.span,
 342                                 "Try not to call a closure in the expression where it is declared.",
 343                                 |db| {
 344                                     if decl.inputs.is_empty() {
 345                                         let hint = snippet(cx, block.span, "..").into_owned();
 346                                         db.span_suggestion(
 347                                             expr.span,
 348                                             "Try doing something like: ",
 349                                             hint,
 350                                             Applicability::MachineApplicable, // snippet
 351                                         );
 352                                     }
 353                                 },
 354                             );
 355                         }
 356                     }
 357                 }
 358             },
 359             ExprKind::Unary(UnOp::Neg, ref inner) => {
 360                 if let ExprKind::Unary(UnOp::Neg, _) = inner.node {
 361                     span_lint(
 362                         cx,
 363                         DOUBLE_NEG,
 364                         expr.span,
 365                         "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 366                     );
 367                 }
 368             },
 369             ExprKind::Lit(ref lit) => self.check_lit(cx, lit),
 370             _ => (),
 371         }
 372     }
 373
 374     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 375         for w in block.stmts.windows(2) {
 376             if_chain! {
 377                 if let StmtKind::Local(ref local) = w[0].node;
 378                 if let Option::Some(ref t) = local.init;
 379                 if let ExprKind::Closure(..) = t.node;
 380                 if let PatKind::Ident(_, ident, _) = local.pat.node;
 381                 if let StmtKind::Semi(ref second) = w[1].node;
 382                 if let ExprKind::Assign(_, ref call) = second.node;
 383                 if let ExprKind::Call(ref closure, _) = call.node;
 384                 if let ExprKind::Path(_, ref path) = closure.node;
 385                 then {
 386                     if ident == path.segments[0].ident {
 387                         span_lint(
 388                             cx,
 389                             REDUNDANT_CLOSURE_CALL,
 390                             second.span,
 391                             "Closure called just once immediately after it was declared",
 392                         );
 393                     }
 394                 }
 395             }
 396         }
 397     }
 398 }
 399
 400 impl MiscEarly {
 401     fn check_lit(self, cx: &EarlyContext<'_>, lit: &Lit) {
 402         if_chain! {
 403             if let LitKind::Int(value, ..) = lit.node;
 404             if let Some(src) = snippet_opt(cx, lit.span);
 405             if let Some(firstch) = src.chars().next();
 406             if char::to_digit(firstch, 10).is_some();
 407             then {
 408                 let mut prev = '\0';
 409                 for ch in src.chars() {
 410                     if ch == 'i' || ch == 'u' {
 411                         if prev != '_' {
 412                             span_lint(cx, UNSEPARATED_LITERAL_SUFFIX, lit.span,
 413                                         "integer type suffix should be separated by an underscore");
 414                         }
 415                         break;
 416                     }
 417                     prev = ch;
 418                 }
 419                 if src.starts_with("0x") {
 420                     let mut seen = (false, false);
 421                     for ch in src.chars() {
 422                         match ch {
 423                             'a' ..= 'f' => seen.0 = true,
 424                             'A' ..= 'F' => seen.1 = true,
 425                             'i' | 'u'   => break,   // start of suffix already
 426                             _ => ()
 427                         }
 428                     }
 429                     if seen.0 && seen.1 {
 430                         span_lint(cx, MIXED_CASE_HEX_LITERALS, lit.span,
 431                                     "inconsistent casing in hexadecimal literal");
 432                     }
 433                 } else if src.starts_with("0b") || src.starts_with("0o") {
 434                     /* nothing to do */
 435                 } else if value != 0 && src.starts_with('0') {
 436                     span_lint_and_then(cx,
 437                                         ZERO_PREFIXED_LITERAL,
 438                                         lit.span,
 439                                         "this is a decimal constant",
 440                                         |db| {
 441                         db.span_suggestion(
 442                             lit.span,
 443                             "if you mean to use a decimal constant, remove the `0` to remove confusion",
 444                             src.trim_start_matches(|c| c == '_' || c == '0').to_string(),
 445                             Applicability::MaybeIncorrect,
 446                         );
 447                         db.span_suggestion(
 448                             lit.span,
 449                             "if you mean to use an octal constant, use `0o`",
 450                             format!("0o{}", src.trim_start_matches(|c| c == '_' || c == '0')),
 451                             Applicability::MaybeIncorrect,
 452                         );
 453                     });
 454                 }
 455             }
 456         }
 457         if_chain! {
 458             if let LitKind::Float(..) = lit.node;
 459             if let Some(src) = snippet_opt(cx, lit.span);
 460             if let Some(firstch) = src.chars().next();
 461             if char::to_digit(firstch, 10).is_some();
 462             then {
 463                 let mut prev = '\0';
 464                 for ch in src.chars() {
 465                     if ch == 'f' {
 466                         if prev != '_' {
 467                             span_lint(cx, UNSEPARATED_LITERAL_SUFFIX, lit.span,
 468                                         "float type suffix should be separated by an underscore");
 469                         }
 470                         break;
 471                     }
 472                     prev = ch;
 473                 }
 474             }
 475         }
 476     }
 477 }