clippy_lints/src/non_expressive_names.rs

   1 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
   2 use rustc_ast::ast::{
   3     Arm, AssocItem, AssocItemKind, Attribute, Block, FnDecl, FnKind, Item, ItemKind, Local, Pat, PatKind,
   4 };
   5 use rustc_ast::visit::{walk_block, walk_expr, walk_pat, Visitor};
   6 use rustc_lint::{EarlyContext, EarlyLintPass};
   7 use rustc_middle::lint::in_external_macro;
   8 use rustc_session::{declare_tool_lint, impl_lint_pass};
   9 use rustc_span::source_map::Span;
  10 use rustc_span::sym;
  11 use rustc_span::symbol::{Ident, Symbol};
  12 use std::cmp::Ordering;
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for names that are very similar and thus confusing.
  16     ///
  17     /// **Why is this bad?** It's hard to distinguish between names that differ only
  18     /// by a single character.
  19     ///
  20     /// **Known problems:** None?
  21     ///
  22     /// **Example:**
  23     /// ```ignore
  24     /// let checked_exp = something;
  25     /// let checked_expr = something_else;
  26     /// ```
  27     pub SIMILAR_NAMES,
  28     pedantic,
  29     "similarly named items and bindings"
  30 }
  31
  32 declare_clippy_lint! {
  33     /// **What it does:** Checks for too many variables whose name consists of a
  34     /// single character.
  35     ///
  36     /// **Why is this bad?** It's hard to memorize what a variable means without a
  37     /// descriptive name.
  38     ///
  39     /// **Known problems:** None?
  40     ///
  41     /// **Example:**
  42     /// ```ignore
  43     /// let (a, b, c, d, e, f, g) = (...);
  44     /// ```
  45     pub MANY_SINGLE_CHAR_NAMES,
  46     style,
  47     "too many single character bindings"
  48 }
  49
  50 declare_clippy_lint! {
  51     /// **What it does:** Checks if you have variables whose name consists of just
  52     /// underscores and digits.
  53     ///
  54     /// **Why is this bad?** It's hard to memorize what a variable means without a
  55     /// descriptive name.
  56     ///
  57     /// **Known problems:** None?
  58     ///
  59     /// **Example:**
  60     /// ```rust
  61     /// let _1 = 1;
  62     /// let ___1 = 1;
  63     /// let __1___2 = 11;
  64     /// ```
  65     pub JUST_UNDERSCORES_AND_DIGITS,
  66     style,
  67     "unclear name"
  68 }
  69
  70 #[derive(Copy, Clone)]
  71 pub struct NonExpressiveNames {
  72     pub single_char_binding_names_threshold: u64,
  73 }
  74
  75 impl_lint_pass!(NonExpressiveNames => [SIMILAR_NAMES, MANY_SINGLE_CHAR_NAMES, JUST_UNDERSCORES_AND_DIGITS]);
  76
  77 struct ExistingName {
  78     interned: Symbol,
  79     span: Span,
  80     len: usize,
  81     exemptions: &'static [&'static str],
  82 }
  83
  84 struct SimilarNamesLocalVisitor<'a, 'tcx> {
  85     names: Vec<ExistingName>,
  86     cx: &'a EarlyContext<'tcx>,
  87     lint: &'a NonExpressiveNames,
  88
  89     /// A stack of scopes containing the single-character bindings in each scope.
  90     single_char_names: Vec<Vec<Ident>>,
  91 }
  92
  93 impl<'a, 'tcx> SimilarNamesLocalVisitor<'a, 'tcx> {
  94     fn check_single_char_names(&self) {
  95         let num_single_char_names = self.single_char_names.iter().flatten().count();
  96         let threshold = self.lint.single_char_binding_names_threshold;
  97         if num_single_char_names as u64 > threshold {
  98             let span = self
  99                 .single_char_names
 100                 .iter()
 101                 .flatten()
 102                 .map(|ident| ident.span)
 103                 .collect::<Vec<_>>();
 104             span_lint(
 105                 self.cx,
 106                 MANY_SINGLE_CHAR_NAMES,
 107                 span,
 108                 &format!(
 109                     "{} bindings with single-character names in scope",
 110                     num_single_char_names
 111                 ),
 112             );
 113         }
 114     }
 115 }
 116
 117 // this list contains lists of names that are allowed to be similar
 118 // the assumption is that no name is ever contained in multiple lists.
 119 #[rustfmt::skip]
 120 const ALLOWED_TO_BE_SIMILAR: &[&[&str]] = &[
 121     &["parsed", "parser"],
 122     &["lhs", "rhs"],
 123     &["tx", "rx"],
 124     &["set", "get"],
 125     &["args", "arms"],
 126     &["qpath", "path"],
 127     &["lit", "lint"],
 128 ];
 129
 130 struct SimilarNamesNameVisitor<'a, 'tcx, 'b>(&'b mut SimilarNamesLocalVisitor<'a, 'tcx>);
 131
 132 impl<'a, 'tcx, 'b> Visitor<'tcx> for SimilarNamesNameVisitor<'a, 'tcx, 'b> {
 133     fn visit_pat(&mut self, pat: &'tcx Pat) {
 134         match pat.kind {
 135             PatKind::Ident(_, ident, _) => {
 136                 if !pat.span.from_expansion() {
 137                     self.check_ident(ident);
 138                 }
 139             },
 140             PatKind::Struct(_, ref fields, _) => {
 141                 for field in fields {
 142                     if !field.is_shorthand {
 143                         self.visit_pat(&field.pat);
 144                     }
 145                 }
 146             },
 147             // just go through the first pattern, as either all patterns
 148             // bind the same bindings or rustc would have errored much earlier
 149             PatKind::Or(ref pats) => self.visit_pat(&pats[0]),
 150             _ => walk_pat(self, pat),
 151         }
 152     }
 153 }
 154
 155 #[must_use]
 156 fn get_exemptions(interned_name: &str) -> Option<&'static [&'static str]> {
 157     for &list in ALLOWED_TO_BE_SIMILAR {
 158         if allowed_to_be_similar(interned_name, list) {
 159             return Some(list);
 160         }
 161     }
 162     None
 163 }
 164
 165 #[must_use]
 166 fn allowed_to_be_similar(interned_name: &str, list: &[&str]) -> bool {
 167     list.iter()
 168         .any(|&name| interned_name.starts_with(name) || interned_name.ends_with(name))
 169 }
 170
 171 impl<'a, 'tcx, 'b> SimilarNamesNameVisitor<'a, 'tcx, 'b> {
 172     fn check_short_ident(&mut self, ident: Ident) {
 173         // Ignore shadowing
 174         if self
 175             .0
 176             .single_char_names
 177             .iter()
 178             .flatten()
 179             .any(|id| id.name == ident.name)
 180         {
 181             return;
 182         }
 183
 184         if let Some(scope) = &mut self.0.single_char_names.last_mut() {
 185             scope.push(ident);
 186         }
 187     }
 188
 189     #[allow(clippy::too_many_lines)]
 190     fn check_ident(&mut self, ident: Ident) {
 191         let interned_name = ident.name.as_str();
 192         if interned_name.chars().any(char::is_uppercase) {
 193             return;
 194         }
 195         if interned_name.chars().all(|c| c.is_digit(10) || c == '_') {
 196             span_lint(
 197                 self.0.cx,
 198                 JUST_UNDERSCORES_AND_DIGITS,
 199                 ident.span,
 200                 "consider choosing a more descriptive name",
 201             );
 202             return;
 203         }
 204         if interned_name.starts_with('_') {
 205             // these bindings are typically unused or represent an ignored portion of a destructuring pattern
 206             return;
 207         }
 208         let count = interned_name.chars().count();
 209         if count < 3 {
 210             if count == 1 {
 211                 self.check_short_ident(ident);
 212             }
 213             return;
 214         }
 215         for existing_name in &self.0.names {
 216             if allowed_to_be_similar(&interned_name, existing_name.exemptions) {
 217                 continue;
 218             }
 219             let mut split_at = None;
 220             match existing_name.len.cmp(&count) {
 221                 Ordering::Greater => {
 222                     if existing_name.len - count != 1
 223                         || levenstein_not_1(&interned_name, &existing_name.interned.as_str())
 224                     {
 225                         continue;
 226                     }
 227                 },
 228                 Ordering::Less => {
 229                     if count - existing_name.len != 1
 230                         || levenstein_not_1(&existing_name.interned.as_str(), &interned_name)
 231                     {
 232                         continue;
 233                     }
 234                 },
 235                 Ordering::Equal => {
 236                     let mut interned_chars = interned_name.chars();
 237                     let interned_str = existing_name.interned.as_str();
 238                     let mut existing_chars = interned_str.chars();
 239                     let first_i = interned_chars.next().expect("we know we have at least one char");
 240                     let first_e = existing_chars.next().expect("we know we have at least one char");
 241                     let eq_or_numeric = |(a, b): (char, char)| a == b || a.is_numeric() && b.is_numeric();
 242
 243                     if eq_or_numeric((first_i, first_e)) {
 244                         let last_i = interned_chars.next_back().expect("we know we have at least two chars");
 245                         let last_e = existing_chars.next_back().expect("we know we have at least two chars");
 246                         if eq_or_numeric((last_i, last_e)) {
 247                             if interned_chars
 248                                 .zip(existing_chars)
 249                                 .filter(|&ie| !eq_or_numeric(ie))
 250                                 .count()
 251                                 != 1
 252                             {
 253                                 continue;
 254                             }
 255                         } else {
 256                             let second_last_i = interned_chars
 257                                 .next_back()
 258                                 .expect("we know we have at least three chars");
 259                             let second_last_e = existing_chars
 260                                 .next_back()
 261                                 .expect("we know we have at least three chars");
 262                             if !eq_or_numeric((second_last_i, second_last_e))
 263                                 || second_last_i == '_'
 264                                 || !interned_chars.zip(existing_chars).all(eq_or_numeric)
 265                             {
 266                                 // allowed similarity foo_x, foo_y
 267                                 // or too many chars differ (foo_x, boo_y) or (foox, booy)
 268                                 continue;
 269                             }
 270                             split_at = interned_name.char_indices().rev().next().map(|(i, _)| i);
 271                         }
 272                     } else {
 273                         let second_i = interned_chars.next().expect("we know we have at least two chars");
 274                         let second_e = existing_chars.next().expect("we know we have at least two chars");
 275                         if !eq_or_numeric((second_i, second_e))
 276                             || second_i == '_'
 277                             || !interned_chars.zip(existing_chars).all(eq_or_numeric)
 278                         {
 279                             // allowed similarity x_foo, y_foo
 280                             // or too many chars differ (x_foo, y_boo) or (xfoo, yboo)
 281                             continue;
 282                         }
 283                         split_at = interned_name.chars().next().map(char::len_utf8);
 284                     }
 285                 },
 286             }
 287             span_lint_and_then(
 288                 self.0.cx,
 289                 SIMILAR_NAMES,
 290                 ident.span,
 291                 "binding's name is too similar to existing binding",
 292                 |diag| {
 293                     diag.span_note(existing_name.span, "existing binding defined here");
 294                     if let Some(split) = split_at {
 295                         diag.span_help(
 296                             ident.span,
 297                             &format!(
 298                                 "separate the discriminating character by an \
 299                                  underscore like: `{}_{}`",
 300                                 &interned_name[..split],
 301                                 &interned_name[split..]
 302                             ),
 303                         );
 304                     }
 305                 },
 306             );
 307             return;
 308         }
 309         self.0.names.push(ExistingName {
 310             exemptions: get_exemptions(&interned_name).unwrap_or(&[]),
 311             interned: ident.name,
 312             span: ident.span,
 313             len: count,
 314         });
 315     }
 316 }
 317
 318 impl<'a, 'b> SimilarNamesLocalVisitor<'a, 'b> {
 319     /// ensure scoping rules work
 320     fn apply<F: for<'c> Fn(&'c mut Self)>(&mut self, f: F) {
 321         let n = self.names.len();
 322         let single_char_count = self.single_char_names.len();
 323         f(self);
 324         self.names.truncate(n);
 325         self.single_char_names.truncate(single_char_count);
 326     }
 327 }
 328
 329 impl<'a, 'tcx> Visitor<'tcx> for SimilarNamesLocalVisitor<'a, 'tcx> {
 330     fn visit_local(&mut self, local: &'tcx Local) {
 331         if let Some(ref init) = local.init {
 332             self.apply(|this| walk_expr(this, &**init));
 333         }
 334         // add the pattern after the expression because the bindings aren't available
 335         // yet in the init
 336         // expression
 337         SimilarNamesNameVisitor(self).visit_pat(&*local.pat);
 338     }
 339     fn visit_block(&mut self, blk: &'tcx Block) {
 340         self.single_char_names.push(vec![]);
 341
 342         self.apply(|this| walk_block(this, blk));
 343
 344         self.check_single_char_names();
 345         self.single_char_names.pop();
 346     }
 347     fn visit_arm(&mut self, arm: &'tcx Arm) {
 348         self.single_char_names.push(vec![]);
 349
 350         self.apply(|this| {
 351             SimilarNamesNameVisitor(this).visit_pat(&arm.pat);
 352             this.apply(|this| walk_expr(this, &arm.body));
 353         });
 354
 355         self.check_single_char_names();
 356         self.single_char_names.pop();
 357     }
 358     fn visit_item(&mut self, _: &Item) {
 359         // do not recurse into inner items
 360     }
 361 }
 362
 363 impl EarlyLintPass for NonExpressiveNames {
 364     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
 365         if in_external_macro(cx.sess, item.span) {
 366             return;
 367         }
 368
 369         if let ItemKind::Fn(box FnKind(_, ref sig, _, Some(ref blk))) = item.kind {
 370             do_check(self, cx, &item.attrs, &sig.decl, blk);
 371         }
 372     }
 373
 374     fn check_impl_item(&mut self, cx: &EarlyContext<'_>, item: &AssocItem) {
 375         if in_external_macro(cx.sess, item.span) {
 376             return;
 377         }
 378
 379         if let AssocItemKind::Fn(box FnKind(_, ref sig, _, Some(ref blk))) = item.kind {
 380             do_check(self, cx, &item.attrs, &sig.decl, blk);
 381         }
 382     }
 383 }
 384
 385 fn do_check(lint: &mut NonExpressiveNames, cx: &EarlyContext<'_>, attrs: &[Attribute], decl: &FnDecl, blk: &Block) {
 386     if !attrs.iter().any(|attr| attr.has_name(sym::test)) {
 387         let mut visitor = SimilarNamesLocalVisitor {
 388             names: Vec::new(),
 389             cx,
 390             lint,
 391             single_char_names: vec![vec![]],
 392         };
 393
 394         // initialize with function arguments
 395         for arg in &decl.inputs {
 396             SimilarNamesNameVisitor(&mut visitor).visit_pat(&arg.pat);
 397         }
 398         // walk all other bindings
 399         walk_block(&mut visitor, blk);
 400
 401         visitor.check_single_char_names();
 402     }
 403 }
 404
 405 /// Precondition: `a_name.chars().count() < b_name.chars().count()`.
 406 #[must_use]
 407 fn levenstein_not_1(a_name: &str, b_name: &str) -> bool {
 408     debug_assert!(a_name.chars().count() < b_name.chars().count());
 409     let mut a_chars = a_name.chars();
 410     let mut b_chars = b_name.chars();
 411     while let (Some(a), Some(b)) = (a_chars.next(), b_chars.next()) {
 412         if a == b {
 413             continue;
 414         }
 415         if let Some(b2) = b_chars.next() {
 416             // check if there's just one character inserted
 417             return a != b2 || a_chars.ne(b_chars);
 418         }
 419         // tuple
 420         // ntuple
 421         return true;
 422     }
 423     // for item in items
 424     true
 425 }