src/tools/clippy/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,
   4     PatKind,
   5 };
   6 use rustc_ast::visit::{walk_block, walk_expr, walk_pat, Visitor};
   7 use rustc_lint::{EarlyContext, EarlyLintPass};
   8 use rustc_middle::lint::in_external_macro;
   9 use rustc_session::{declare_tool_lint, impl_lint_pass};
  10 use rustc_span::source_map::Span;
  11 use rustc_span::sym;
  12 use rustc_span::symbol::{Ident, Symbol};
  13 use std::cmp::Ordering;
  14
  15 declare_clippy_lint! {
  16     /// **What it does:** Checks for names that are very similar and thus confusing.
  17     ///
  18     /// **Why is this bad?** It's hard to distinguish between names that differ only
  19     /// by a single character.
  20     ///
  21     /// **Known problems:** None?
  22     ///
  23     /// **Example:**
  24     /// ```ignore
  25     /// let checked_exp = something;
  26     /// let checked_expr = something_else;
  27     /// ```
  28     pub SIMILAR_NAMES,
  29     pedantic,
  30     "similarly named items and bindings"
  31 }
  32
  33 declare_clippy_lint! {
  34     /// **What it does:** Checks for too many variables whose name consists of a
  35     /// single character.
  36     ///
  37     /// **Why is this bad?** It's hard to memorize what a variable means without a
  38     /// descriptive name.
  39     ///
  40     /// **Known problems:** None?
  41     ///
  42     /// **Example:**
  43     /// ```ignore
  44     /// let (a, b, c, d, e, f, g) = (...);
  45     /// ```
  46     pub MANY_SINGLE_CHAR_NAMES,
  47     style,
  48     "too many single character bindings"
  49 }
  50
  51 declare_clippy_lint! {
  52     /// **What it does:** Checks if you have variables whose name consists of just
  53     /// underscores and digits.
  54     ///
  55     /// **Why is this bad?** It's hard to memorize what a variable means without a
  56     /// descriptive name.
  57     ///
  58     /// **Known problems:** None?
  59     ///
  60     /// **Example:**
  61     /// ```rust
  62     /// let _1 = 1;
  63     /// let ___1 = 1;
  64     /// let __1___2 = 11;
  65     /// ```
  66     pub JUST_UNDERSCORES_AND_DIGITS,
  67     style,
  68     "unclear name"
  69 }
  70
  71 #[derive(Copy, Clone)]
  72 pub struct NonExpressiveNames {
  73     pub single_char_binding_names_threshold: u64,
  74 }
  75
  76 impl_lint_pass!(NonExpressiveNames => [SIMILAR_NAMES, MANY_SINGLE_CHAR_NAMES, JUST_UNDERSCORES_AND_DIGITS]);
  77
  78 struct ExistingName {
  79     interned: Symbol,
  80     span: Span,
  81     len: usize,
  82     exemptions: &'static [&'static str],
  83 }
  84
  85 struct SimilarNamesLocalVisitor<'a, 'tcx> {
  86     names: Vec<ExistingName>,
  87     cx: &'a EarlyContext<'tcx>,
  88     lint: &'a NonExpressiveNames,
  89
  90     /// A stack of scopes containing the single-character bindings in each scope.
  91     single_char_names: Vec<Vec<Ident>>,
  92 }
  93
  94 impl<'a, 'tcx> SimilarNamesLocalVisitor<'a, 'tcx> {
  95     fn check_single_char_names(&self) {
  96         let num_single_char_names = self.single_char_names.iter().flatten().count();
  97         let threshold = self.lint.single_char_binding_names_threshold;
  98         if num_single_char_names as u64 > threshold {
  99             let span = self
 100                 .single_char_names
 101                 .iter()
 102                 .flatten()
 103                 .map(|ident| ident.span)
 104                 .collect::<Vec<_>>();
 105             span_lint(
 106                 self.cx,
 107                 MANY_SINGLE_CHAR_NAMES,
 108                 span,
 109                 &format!(
 110                     "{} bindings with single-character names in scope",
 111                     num_single_char_names
 112                 ),
 113             );
 114         }
 115     }
 116 }
 117
 118 // this list contains lists of names that are allowed to be similar
 119 // the assumption is that no name is ever contained in multiple lists.
 120 #[rustfmt::skip]
 121 const ALLOWED_TO_BE_SIMILAR: &[&[&str]] = &[
 122     &["parsed", "parser"],
 123     &["lhs", "rhs"],
 124     &["tx", "rx"],
 125     &["set", "get"],
 126     &["args", "arms"],
 127     &["qpath", "path"],
 128     &["lit", "lint"],
 129 ];
 130
 131 struct SimilarNamesNameVisitor<'a, 'tcx, 'b>(&'b mut SimilarNamesLocalVisitor<'a, 'tcx>);
 132
 133 impl<'a, 'tcx, 'b> Visitor<'tcx> for SimilarNamesNameVisitor<'a, 'tcx, 'b> {
 134     fn visit_pat(&mut self, pat: &'tcx Pat) {
 135         match pat.kind {
 136             PatKind::Ident(_, ident, _) => {
 137                 if !pat.span.from_expansion() {
 138                     self.check_ident(ident);
 139                 }
 140             },
 141             PatKind::Struct(_, ref fields, _) => {
 142                 for field in fields {
 143                     if !field.is_shorthand {
 144                         self.visit_pat(&field.pat);
 145                     }
 146                 }
 147             },
 148             // just go through the first pattern, as either all patterns
 149             // bind the same bindings or rustc would have errored much earlier
 150             PatKind::Or(ref pats) => self.visit_pat(&pats[0]),
 151             _ => walk_pat(self, pat),
 152         }
 153     }
 154 }
 155
 156 #[must_use]
 157 fn get_exemptions(interned_name: &str) -> Option<&'static [&'static str]> {
 158     for &list in ALLOWED_TO_BE_SIMILAR {
 159         if allowed_to_be_similar(interned_name, list) {
 160             return Some(list);
 161         }
 162     }
 163     None
 164 }
 165
 166 #[must_use]
 167 fn allowed_to_be_similar(interned_name: &str, list: &[&str]) -> bool {
 168     list.iter()
 169         .any(|&name| interned_name.starts_with(name) || interned_name.ends_with(name))
 170 }
 171
 172 impl<'a, 'tcx, 'b> SimilarNamesNameVisitor<'a, 'tcx, 'b> {
 173     fn check_short_ident(&mut self, ident: Ident) {
 174         // Ignore shadowing
 175         if self
 176             .0
 177             .single_char_names
 178             .iter()
 179             .flatten()
 180             .any(|id| id.name == ident.name)
 181         {
 182             return;
 183         }
 184
 185         if let Some(scope) = &mut self.0.single_char_names.last_mut() {
 186             scope.push(ident);
 187         }
 188     }
 189
 190     #[allow(clippy::too_many_lines)]
 191     fn check_ident(&mut self, ident: Ident) {
 192         let interned_name = ident.name.as_str();
 193         if interned_name.chars().any(char::is_uppercase) {
 194             return;
 195         }
 196         if interned_name.chars().all(|c| c.is_digit(10) || c == '_') {
 197             span_lint(
 198                 self.0.cx,
 199                 JUST_UNDERSCORES_AND_DIGITS,
 200                 ident.span,
 201                 "consider choosing a more descriptive name",
 202             );
 203             return;
 204         }
 205         if interned_name.starts_with('_') {
 206             // these bindings are typically unused or represent an ignored portion of a destructuring pattern
 207             return;
 208         }
 209         let count = interned_name.chars().count();
 210         if count < 3 {
 211             if count == 1 {
 212                 self.check_short_ident(ident);
 213             }
 214             return;
 215         }
 216         for existing_name in &self.0.names {
 217             if allowed_to_be_similar(&interned_name, existing_name.exemptions) {
 218                 continue;
 219             }
 220             let mut split_at = None;
 221             match existing_name.len.cmp(&count) {
 222                 Ordering::Greater => {
 223                     if existing_name.len - count != 1
 224                         || levenstein_not_1(&interned_name, &existing_name.interned.as_str())
 225                     {
 226                         continue;
 227                     }
 228                 },
 229                 Ordering::Less => {
 230                     if count - existing_name.len != 1
 231                         || levenstein_not_1(&existing_name.interned.as_str(), &interned_name)
 232                     {
 233                         continue;
 234                     }
 235                 },
 236                 Ordering::Equal => {
 237                     let mut interned_chars = interned_name.chars();
 238                     let interned_str = existing_name.interned.as_str();
 239                     let mut existing_chars = interned_str.chars();
 240                     let first_i = interned_chars.next().expect("we know we have at least one char");
 241                     let first_e = existing_chars.next().expect("we know we have at least one char");
 242                     let eq_or_numeric = |(a, b): (char, char)| a == b || a.is_numeric() && b.is_numeric();
 243
 244                     if eq_or_numeric((first_i, first_e)) {
 245                         let last_i = interned_chars.next_back().expect("we know we have at least two chars");
 246                         let last_e = existing_chars.next_back().expect("we know we have at least two chars");
 247                         if eq_or_numeric((last_i, last_e)) {
 248                             if interned_chars
 249                                 .zip(existing_chars)
 250                                 .filter(|&ie| !eq_or_numeric(ie))
 251                                 .count()
 252                                 != 1
 253                             {
 254                                 continue;
 255                             }
 256                         } else {
 257                             let second_last_i = interned_chars
 258                                 .next_back()
 259                                 .expect("we know we have at least three chars");
 260                             let second_last_e = existing_chars
 261                                 .next_back()
 262                                 .expect("we know we have at least three chars");
 263                             if !eq_or_numeric((second_last_i, second_last_e))
 264                                 || second_last_i == '_'
 265                                 || !interned_chars.zip(existing_chars).all(eq_or_numeric)
 266                             {
 267                                 // allowed similarity foo_x, foo_y
 268                                 // or too many chars differ (foo_x, boo_y) or (foox, booy)
 269                                 continue;
 270                             }
 271                             split_at = interned_name.char_indices().rev().next().map(|(i, _)| i);
 272                         }
 273                     } else {
 274                         let second_i = interned_chars.next().expect("we know we have at least two chars");
 275                         let second_e = existing_chars.next().expect("we know we have at least two chars");
 276                         if !eq_or_numeric((second_i, second_e))
 277                             || second_i == '_'
 278                             || !interned_chars.zip(existing_chars).all(eq_or_numeric)
 279                         {
 280                             // allowed similarity x_foo, y_foo
 281                             // or too many chars differ (x_foo, y_boo) or (xfoo, yboo)
 282                             continue;
 283                         }
 284                         split_at = interned_name.chars().next().map(char::len_utf8);
 285                     }
 286                 },
 287             }
 288             span_lint_and_then(
 289                 self.0.cx,
 290                 SIMILAR_NAMES,
 291                 ident.span,
 292                 "binding's name is too similar to existing binding",
 293                 |diag| {
 294                     diag.span_note(existing_name.span, "existing binding defined here");
 295                     if let Some(split) = split_at {
 296                         diag.span_help(
 297                             ident.span,
 298                             &format!(
 299                                 "separate the discriminating character by an \
 300                                  underscore like: `{}_{}`",
 301                                 &interned_name[..split],
 302                                 &interned_name[split..]
 303                             ),
 304                         );
 305                     }
 306                 },
 307             );
 308             return;
 309         }
 310         self.0.names.push(ExistingName {
 311             exemptions: get_exemptions(&interned_name).unwrap_or(&[]),
 312             interned: ident.name,
 313             span: ident.span,
 314             len: count,
 315         });
 316     }
 317 }
 318
 319 impl<'a, 'b> SimilarNamesLocalVisitor<'a, 'b> {
 320     /// ensure scoping rules work
 321     fn apply<F: for<'c> Fn(&'c mut Self)>(&mut self, f: F) {
 322         let n = self.names.len();
 323         let single_char_count = self.single_char_names.len();
 324         f(self);
 325         self.names.truncate(n);
 326         self.single_char_names.truncate(single_char_count);
 327     }
 328 }
 329
 330 impl<'a, 'tcx> Visitor<'tcx> for SimilarNamesLocalVisitor<'a, 'tcx> {
 331     fn visit_local(&mut self, local: &'tcx Local) {
 332         if let Some(ref init) = local.init {
 333             self.apply(|this| walk_expr(this, &**init));
 334         }
 335         // add the pattern after the expression because the bindings aren't available
 336         // yet in the init
 337         // expression
 338         SimilarNamesNameVisitor(self).visit_pat(&*local.pat);
 339     }
 340     fn visit_block(&mut self, blk: &'tcx Block) {
 341         self.single_char_names.push(vec![]);
 342
 343         self.apply(|this| walk_block(this, blk));
 344
 345         self.check_single_char_names();
 346         self.single_char_names.pop();
 347     }
 348     fn visit_arm(&mut self, arm: &'tcx Arm) {
 349         self.single_char_names.push(vec![]);
 350
 351         self.apply(|this| {
 352             SimilarNamesNameVisitor(this).visit_pat(&arm.pat);
 353             this.apply(|this| walk_expr(this, &arm.body));
 354         });
 355
 356         self.check_single_char_names();
 357         self.single_char_names.pop();
 358     }
 359     fn visit_item(&mut self, _: &Item) {
 360         // do not recurse into inner items
 361     }
 362 }
 363
 364 impl EarlyLintPass for NonExpressiveNames {
 365     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
 366         if in_external_macro(cx.sess, item.span) {
 367             return;
 368         }
 369
 370         if let ItemKind::Fn(box FnKind(_, ref sig, _, Some(ref blk))) = item.kind {
 371             do_check(self, cx, &item.attrs, &sig.decl, blk);
 372         }
 373     }
 374
 375     fn check_impl_item(&mut self, cx: &EarlyContext<'_>, item: &AssocItem) {
 376         if in_external_macro(cx.sess, item.span) {
 377             return;
 378         }
 379
 380         if let AssocItemKind::Fn(box FnKind(_, ref sig, _, Some(ref blk))) = item.kind {
 381             do_check(self, cx, &item.attrs, &sig.decl, blk);
 382         }
 383     }
 384 }
 385
 386 fn do_check(lint: &mut NonExpressiveNames, cx: &EarlyContext<'_>, attrs: &[Attribute], decl: &FnDecl, blk: &Block) {
 387     if !attrs.iter().any(|attr| attr.has_name(sym::test)) {
 388         let mut visitor = SimilarNamesLocalVisitor {
 389             names: Vec::new(),
 390             cx,
 391             lint,
 392             single_char_names: vec![vec![]],
 393         };
 394
 395         // initialize with function arguments
 396         for arg in &decl.inputs {
 397             SimilarNamesNameVisitor(&mut visitor).visit_pat(&arg.pat);
 398         }
 399         // walk all other bindings
 400         walk_block(&mut visitor, blk);
 401
 402         visitor.check_single_char_names();
 403     }
 404 }
 405
 406 /// Precondition: `a_name.chars().count() < b_name.chars().count()`.
 407 #[must_use]
 408 fn levenstein_not_1(a_name: &str, b_name: &str) -> bool {
 409     debug_assert!(a_name.chars().count() < b_name.chars().count());
 410     let mut a_chars = a_name.chars();
 411     let mut b_chars = b_name.chars();
 412     while let (Some(a), Some(b)) = (a_chars.next(), b_chars.next()) {
 413         if a == b {
 414             continue;
 415         }
 416         if let Some(b2) = b_chars.next() {
 417             // check if there's just one character inserted
 418             return a != b2 || a_chars.ne(b_chars);
 419         }
 420         // tuple
 421         // ntuple
 422         return true;
 423     }
 424     // for item in items
 425     true
 426 }