clippy_lints/src/misc_early.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 use crate::rustc::lint::{in_external_macro, EarlyContext, EarlyLintPass, LintArray, LintContext, LintPass};
  11 use crate::rustc::{declare_tool_lint, lint_array};
  12 use crate::rustc_data_structures::fx::FxHashMap;
  13 use crate::rustc_errors::Applicability;
  14 use crate::syntax::ast::*;
  15 use crate::syntax::source_map::Span;
  16 use crate::syntax::visit::{walk_expr, FnKind, Visitor};
  17 use crate::utils::{constants, snippet, snippet_opt, span_help_and_lint, span_lint, span_lint_and_then};
  18 use if_chain::if_chain;
  19 use std::char;
  20
  21 /// **What it does:** Checks for structure field patterns bound to wildcards.
  22 ///
  23 /// **Why is this bad?** Using `..` instead is shorter and leaves the focus on
  24 /// the fields that are actually bound.
  25 ///
  26 /// **Known problems:** None.
  27 ///
  28 /// **Example:**
  29 /// ```rust
  30 /// let { a: _, b: ref b, c: _ } = ..
  31 /// ```
  32 declare_clippy_lint! {
  33     pub UNNEEDED_FIELD_PATTERN,
  34     style,
  35     "struct fields bound to a wildcard instead of using `..`"
  36 }
  37
  38 /// **What it does:** Checks for function arguments having the similar names
  39 /// differing by an underscore.
  40 ///
  41 /// **Why is this bad?** It affects code readability.
  42 ///
  43 /// **Known problems:** None.
  44 ///
  45 /// **Example:**
  46 /// ```rust
  47 /// fn foo(a: i32, _a: i32) {}
  48 /// ```
  49 declare_clippy_lint! {
  50     pub DUPLICATE_UNDERSCORE_ARGUMENT,
  51     style,
  52     "function arguments having names which only differ by an underscore"
  53 }
  54
  55 /// **What it does:** Detects closures called in the same expression where they
  56 /// are defined.
  57 ///
  58 /// **Why is this bad?** It is unnecessarily adding to the expression's
  59 /// complexity.
  60 ///
  61 /// **Known problems:** None.
  62 ///
  63 /// **Example:**
  64 /// ```rust
  65 /// (|| 42)()
  66 /// ```
  67 declare_clippy_lint! {
  68     pub REDUNDANT_CLOSURE_CALL,
  69     complexity,
  70     "throwaway closures called in the expression they are defined"
  71 }
  72
  73 /// **What it does:** Detects expressions of the form `--x`.
  74 ///
  75 /// **Why is this bad?** It can mislead C/C++ programmers to think `x` was
  76 /// decremented.
  77 ///
  78 /// **Known problems:** None.
  79 ///
  80 /// **Example:**
  81 /// ```rust
  82 /// --x;
  83 /// ```
  84 declare_clippy_lint! {
  85     pub DOUBLE_NEG,
  86     style,
  87     "`--x`, which is a double negation of `x` and not a pre-decrement as in C/C++"
  88 }
  89
  90 /// **What it does:** Warns on hexadecimal literals with mixed-case letter
  91 /// digits.
  92 ///
  93 /// **Why is this bad?** It looks confusing.
  94 ///
  95 /// **Known problems:** None.
  96 ///
  97 /// **Example:**
  98 /// ```rust
  99 /// let y = 0x1a9BAcD;
 100 /// ```
 101 declare_clippy_lint! {
 102     pub MIXED_CASE_HEX_LITERALS,
 103     style,
 104     "hex literals whose letter digits are not consistently upper- or lowercased"
 105 }
 106
 107 /// **What it does:** Warns if literal suffixes are not separated by an
 108 /// underscore.
 109 ///
 110 /// **Why is this bad?** It is much less readable.
 111 ///
 112 /// **Known problems:** None.
 113 ///
 114 /// **Example:**
 115 /// ```rust
 116 /// let y = 123832i32;
 117 /// ```
 118 declare_clippy_lint! {
 119     pub UNSEPARATED_LITERAL_SUFFIX,
 120     pedantic,
 121     "literals whose suffix is not separated by an underscore"
 122 }
 123
 124 /// **What it does:** Warns if an integral constant literal starts with `0`.
 125 ///
 126 /// **Why is this bad?** In some languages (including the infamous C language
 127 /// and most of its
 128 /// family), this marks an octal constant. In Rust however, this is a decimal
 129 /// constant. This could
 130 /// be confusing for both the writer and a reader of the constant.
 131 ///
 132 /// **Known problems:** None.
 133 ///
 134 /// **Example:**
 135 ///
 136 /// In Rust:
 137 /// ```rust
 138 /// fn main() {
 139 ///     let a = 0123;
 140 ///     println!("{}", a);
 141 /// }
 142 /// ```
 143 ///
 144 /// prints `123`, while in C:
 145 ///
 146 /// ```c
 147 /// #include <stdio.h>
 148 ///
 149 /// int main() {
 150 ///     int a = 0123;
 151 ///     printf("%d\n", a);
 152 /// }
 153 /// ```
 154 ///
 155 /// prints `83` (as `83 == 0o123` while `123 == 0o173`).
 156 declare_clippy_lint! {
 157     pub ZERO_PREFIXED_LITERAL,
 158     complexity,
 159     "integer literals starting with `0`"
 160 }
 161
 162 /// **What it does:** Warns if a generic shadows a built-in type.
 163 ///
 164 /// **Why is this bad?** This gives surprising type errors.
 165 ///
 166 /// **Known problems:** None.
 167 ///
 168 /// **Example:**
 169 ///
 170 /// ```rust
 171 /// impl<u32> Foo<u32> {
 172 ///     fn impl_func(&self) -> u32 {
 173 ///         42
 174 ///     }
 175 /// }
 176 /// ```
 177 declare_clippy_lint! {
 178     pub BUILTIN_TYPE_SHADOW,
 179     style,
 180     "shadowing a builtin type"
 181 }
 182
 183 #[derive(Copy, Clone)]
 184 pub struct MiscEarly;
 185
 186 impl LintPass for MiscEarly {
 187     fn get_lints(&self) -> LintArray {
 188         lint_array!(
 189             UNNEEDED_FIELD_PATTERN,
 190             DUPLICATE_UNDERSCORE_ARGUMENT,
 191             REDUNDANT_CLOSURE_CALL,
 192             DOUBLE_NEG,
 193             MIXED_CASE_HEX_LITERALS,
 194             UNSEPARATED_LITERAL_SUFFIX,
 195             ZERO_PREFIXED_LITERAL,
 196             BUILTIN_TYPE_SHADOW
 197         )
 198     }
 199 }
 200
 201 // Used to find `return` statements or equivalents e.g. `?`
 202 struct ReturnVisitor {
 203     found_return: bool,
 204 }
 205
 206 impl ReturnVisitor {
 207     fn new() -> Self {
 208         Self { found_return: false }
 209     }
 210 }
 211
 212 impl<'ast> Visitor<'ast> for ReturnVisitor {
 213     fn visit_expr(&mut self, ex: &'ast Expr) {
 214         if let ExprKind::Ret(_) = ex.node {
 215             self.found_return = true;
 216         } else if let ExprKind::Try(_) = ex.node {
 217             self.found_return = true;
 218         }
 219
 220         walk_expr(self, ex)
 221     }
 222 }
 223
 224 impl EarlyLintPass for MiscEarly {
 225     fn check_generics(&mut self, cx: &EarlyContext<'_>, gen: &Generics) {
 226         for param in &gen.params {
 227             if let GenericParamKind::Type { .. } = param.kind {
 228                 let name = param.ident.as_str();
 229                 if constants::BUILTIN_TYPES.contains(&&*name) {
 230                     span_lint(
 231                         cx,
 232                         BUILTIN_TYPE_SHADOW,
 233                         param.ident.span,
 234                         &format!("This generic shadows the built-in type `{}`", name),
 235                     );
 236                 }
 237             }
 238         }
 239     }
 240
 241     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &Pat, _: &mut bool) {
 242         if let PatKind::Struct(ref npat, ref pfields, _) = pat.node {
 243             let mut wilds = 0;
 244             let type_name = npat
 245                 .segments
 246                 .last()
 247                 .expect("A path must have at least one segment")
 248                 .ident
 249                 .name;
 250
 251             for field in pfields {
 252                 if let PatKind::Wild = field.node.pat.node {
 253                     wilds += 1;
 254                 }
 255             }
 256             if !pfields.is_empty() && wilds == pfields.len() {
 257                 span_help_and_lint(
 258                     cx,
 259                     UNNEEDED_FIELD_PATTERN,
 260                     pat.span,
 261                     "All the struct fields are matched to a wildcard pattern, consider using `..`.",
 262                     &format!("Try with `{} {{ .. }}` instead", type_name),
 263                 );
 264                 return;
 265             }
 266             if wilds > 0 {
 267                 let mut normal = vec![];
 268
 269                 for field in pfields {
 270                     match field.node.pat.node {
 271                         PatKind::Wild => {},
 272                         _ => {
 273                             if let Ok(n) = cx.sess().source_map().span_to_snippet(field.span) {
 274                                 normal.push(n);
 275                             }
 276                         },
 277                     }
 278                 }
 279                 for field in pfields {
 280                     if let PatKind::Wild = field.node.pat.node {
 281                         wilds -= 1;
 282                         if wilds > 0 {
 283                             span_lint(
 284                                 cx,
 285                                 UNNEEDED_FIELD_PATTERN,
 286                                 field.span,
 287                                 "You matched a field with a wildcard pattern. Consider using `..` instead",
 288                             );
 289                         } else {
 290                             span_help_and_lint(
 291                                 cx,
 292                                 UNNEEDED_FIELD_PATTERN,
 293                                 field.span,
 294                                 "You matched a field with a wildcard pattern. Consider using `..` \
 295                                  instead",
 296                                 &format!("Try with `{} {{ {}, .. }}`", type_name, normal[..].join(", ")),
 297                             );
 298                         }
 299                     }
 300                 }
 301             }
 302         }
 303     }
 304
 305     fn check_fn(&mut self, cx: &EarlyContext<'_>, _: FnKind<'_>, decl: &FnDecl, _: Span, _: NodeId) {
 306         let mut registered_names: FxHashMap<String, Span> = FxHashMap::default();
 307
 308         for arg in &decl.inputs {
 309             if let PatKind::Ident(_, ident, None) = arg.pat.node {
 310                 let arg_name = ident.to_string();
 311
 312                 if arg_name.starts_with('_') {
 313                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 314                         span_lint(
 315                             cx,
 316                             DUPLICATE_UNDERSCORE_ARGUMENT,
 317                             *correspondence,
 318                             &format!(
 319                                 "`{}` already exists, having another argument having almost the same \
 320                                  name makes code comprehension and documentation more difficult",
 321                                 arg_name[1..].to_owned()
 322                             ),
 323                         );;
 324                     }
 325                 } else {
 326                     registered_names.insert(arg_name, arg.pat.span);
 327                 }
 328             }
 329         }
 330     }
 331
 332     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 333         if in_external_macro(cx.sess(), expr.span) {
 334             return;
 335         }
 336         match expr.node {
 337             ExprKind::Call(ref paren, _) => {
 338                 if let ExprKind::Paren(ref closure) = paren.node {
 339                     if let ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.node {
 340                         let mut visitor = ReturnVisitor::new();
 341                         visitor.visit_expr(block);
 342                         if !visitor.found_return {
 343                             span_lint_and_then(
 344                                 cx,
 345                                 REDUNDANT_CLOSURE_CALL,
 346                                 expr.span,
 347                                 "Try not to call a closure in the expression where it is declared.",
 348                                 |db| {
 349                                     if decl.inputs.is_empty() {
 350                                         let hint = snippet(cx, block.span, "..").into_owned();
 351                                         db.span_suggestion_with_applicability(
 352                                             expr.span,
 353                                             "Try doing something like: ",
 354                                             hint,
 355                                             Applicability::MachineApplicable, // snippet
 356                                         );
 357                                     }
 358                                 },
 359                             );
 360                         }
 361                     }
 362                 }
 363             },
 364             ExprKind::Unary(UnOp::Neg, ref inner) => {
 365                 if let ExprKind::Unary(UnOp::Neg, _) = inner.node {
 366                     span_lint(
 367                         cx,
 368                         DOUBLE_NEG,
 369                         expr.span,
 370                         "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 371                     );
 372                 }
 373             },
 374             ExprKind::Lit(ref lit) => self.check_lit(cx, lit),
 375             _ => (),
 376         }
 377     }
 378
 379     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 380         for w in block.stmts.windows(2) {
 381             if_chain! {
 382                 if let StmtKind::Local(ref local) = w[0].node;
 383                 if let Option::Some(ref t) = local.init;
 384                 if let ExprKind::Closure(..) = t.node;
 385                 if let PatKind::Ident(_, ident, _) = local.pat.node;
 386                 if let StmtKind::Semi(ref second) = w[1].node;
 387                 if let ExprKind::Assign(_, ref call) = second.node;
 388                 if let ExprKind::Call(ref closure, _) = call.node;
 389                 if let ExprKind::Path(_, ref path) = closure.node;
 390                 then {
 391                     if ident == path.segments[0].ident {
 392                         span_lint(
 393                             cx,
 394                             REDUNDANT_CLOSURE_CALL,
 395                             second.span,
 396                             "Closure called just once immediately after it was declared",
 397                         );
 398                     }
 399                 }
 400             }
 401         }
 402     }
 403 }
 404
 405 impl MiscEarly {
 406     fn check_lit(self, cx: &EarlyContext<'_>, lit: &Lit) {
 407         if_chain! {
 408             if let LitKind::Int(value, ..) = lit.node;
 409             if let Some(src) = snippet_opt(cx, lit.span);
 410             if let Some(firstch) = src.chars().next();
 411             if char::to_digit(firstch, 10).is_some();
 412             then {
 413                 let mut prev = '\0';
 414                 for ch in src.chars() {
 415                     if ch == 'i' || ch == 'u' {
 416                         if prev != '_' {
 417                             span_lint(cx, UNSEPARATED_LITERAL_SUFFIX, lit.span,
 418                                         "integer type suffix should be separated by an underscore");
 419                         }
 420                         break;
 421                     }
 422                     prev = ch;
 423                 }
 424                 if src.starts_with("0x") {
 425                     let mut seen = (false, false);
 426                     for ch in src.chars() {
 427                         match ch {
 428                             'a' ..= 'f' => seen.0 = true,
 429                             'A' ..= 'F' => seen.1 = true,
 430                             'i' | 'u'   => break,   // start of suffix already
 431                             _ => ()
 432                         }
 433                     }
 434                     if seen.0 && seen.1 {
 435                         span_lint(cx, MIXED_CASE_HEX_LITERALS, lit.span,
 436                                     "inconsistent casing in hexadecimal literal");
 437                     }
 438                 } else if src.starts_with("0b") || src.starts_with("0o") {
 439                     /* nothing to do */
 440                 } else if value != 0 && src.starts_with('0') {
 441                     span_lint_and_then(cx,
 442                                         ZERO_PREFIXED_LITERAL,
 443                                         lit.span,
 444                                         "this is a decimal constant",
 445                                         |db| {
 446                         db.span_suggestion_with_applicability(
 447                             lit.span,
 448                             "if you mean to use a decimal constant, remove the `0` to remove confusion",
 449                             src.trim_left_matches(|c| c == '_' || c == '0').to_string(),
 450                             Applicability::MaybeIncorrect,
 451                         );
 452                         db.span_suggestion_with_applicability(
 453                             lit.span,
 454                             "if you mean to use an octal constant, use `0o`",
 455                             format!("0o{}", src.trim_left_matches(|c| c == '_' || c == '0')),
 456                             Applicability::MaybeIncorrect,
 457                         );
 458                     });
 459                 }
 460             }
 461         }
 462         if_chain! {
 463             if let LitKind::Float(..) = lit.node;
 464             if let Some(src) = snippet_opt(cx, lit.span);
 465             if let Some(firstch) = src.chars().next();
 466             if char::to_digit(firstch, 10).is_some();
 467             then {
 468                 let mut prev = '\0';
 469                 for ch in src.chars() {
 470                     if ch == 'f' {
 471                         if prev != '_' {
 472                             span_lint(cx, UNSEPARATED_LITERAL_SUFFIX, lit.span,
 473                                         "float type suffix should be separated by an underscore");
 474                         }
 475                         break;
 476                     }
 477                     prev = ch;
 478                 }
 479             }
 480         }
 481     }
 482 }