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