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     &["wparam", "lparam"],
 130 ];
 131
 132 struct SimilarNamesNameVisitor<'a, 'tcx, 'b>(&'b mut SimilarNamesLocalVisitor<'a, 'tcx>);
 133
 134 impl<'a, 'tcx, 'b> Visitor<'tcx> for SimilarNamesNameVisitor<'a, 'tcx, 'b> {
 135     fn visit_pat(&mut self, pat: &'tcx Pat) {
 136         match pat.kind {
 137             PatKind::Ident(_, ident, _) => {
 138                 if !pat.span.from_expansion() {
 139                     self.check_ident(ident);
 140                 }
 141             },
 142             PatKind::Struct(_, _, ref fields, _) => {
 143                 for field in fields {
 144                     if !field.is_shorthand {
 145                         self.visit_pat(&field.pat);
 146                     }
 147                 }
 148             },
 149             // just go through the first pattern, as either all patterns
 150             // bind the same bindings or rustc would have errored much earlier
 151             PatKind::Or(ref pats) => self.visit_pat(&pats[0]),
 152             _ => walk_pat(self, pat),
 153         }
 154     }
 155 }
 156
 157 #[must_use]
 158 fn get_exemptions(interned_name: &str) -> Option<&'static [&'static str]> {
 159     for &list in ALLOWED_TO_BE_SIMILAR {
 160         if allowed_to_be_similar(interned_name, list) {
 161             return Some(list);
 162         }
 163     }
 164     None
 165 }
 166
 167 #[must_use]
 168 fn allowed_to_be_similar(interned_name: &str, list: &[&str]) -> bool {
 169     list.iter()
 170         .any(|&name| interned_name.starts_with(name) || interned_name.ends_with(name))
 171 }
 172
 173 impl<'a, 'tcx, 'b> SimilarNamesNameVisitor<'a, 'tcx, 'b> {
 174     fn check_short_ident(&mut self, ident: Ident) {
 175         // Ignore shadowing
 176         if self
 177             .0
 178             .single_char_names
 179             .iter()
 180             .flatten()
 181             .any(|id| id.name == ident.name)
 182         {
 183             return;
 184         }
 185
 186         if let Some(scope) = &mut self.0.single_char_names.last_mut() {
 187             scope.push(ident);
 188         }
 189     }
 190
 191     #[allow(clippy::too_many_lines)]
 192     fn check_ident(&mut self, ident: Ident) {
 193         let interned_name = ident.name.as_str();
 194         if interned_name.chars().any(char::is_uppercase) {
 195             return;
 196         }
 197         if interned_name.chars().all(|c| c.is_digit(10) || c == '_') {
 198             span_lint(
 199                 self.0.cx,
 200                 JUST_UNDERSCORES_AND_DIGITS,
 201                 ident.span,
 202                 "consider choosing a more descriptive name",
 203             );
 204             return;
 205         }
 206         if interned_name.starts_with('_') {
 207             // these bindings are typically unused or represent an ignored portion of a destructuring pattern
 208             return;
 209         }
 210         let count = interned_name.chars().count();
 211         if count < 3 {
 212             if count == 1 {
 213                 self.check_short_ident(ident);
 214             }
 215             return;
 216         }
 217         for existing_name in &self.0.names {
 218             if allowed_to_be_similar(&interned_name, existing_name.exemptions) {
 219                 continue;
 220             }
 221             let mut split_at = None;
 222             match existing_name.len.cmp(&count) {
 223                 Ordering::Greater => {
 224                     if existing_name.len - count != 1
 225                         || levenstein_not_1(&interned_name, &existing_name.interned.as_str())
 226                     {
 227                         continue;
 228                     }
 229                 },
 230                 Ordering::Less => {
 231                     if count - existing_name.len != 1
 232                         || levenstein_not_1(&existing_name.interned.as_str(), &interned_name)
 233                     {
 234                         continue;
 235                     }
 236                 },
 237                 Ordering::Equal => {
 238                     let mut interned_chars = interned_name.chars();
 239                     let interned_str = existing_name.interned.as_str();
 240                     let mut existing_chars = interned_str.chars();
 241                     let first_i = interned_chars.next().expect("we know we have at least one char");
 242                     let first_e = existing_chars.next().expect("we know we have at least one char");
 243                     let eq_or_numeric = |(a, b): (char, char)| a == b || a.is_numeric() && b.is_numeric();
 244
 245                     if eq_or_numeric((first_i, first_e)) {
 246                         let last_i = interned_chars.next_back().expect("we know we have at least two chars");
 247                         let last_e = existing_chars.next_back().expect("we know we have at least two chars");
 248                         if eq_or_numeric((last_i, last_e)) {
 249                             if interned_chars
 250                                 .zip(existing_chars)
 251                                 .filter(|&ie| !eq_or_numeric(ie))
 252                                 .count()
 253                                 != 1
 254                             {
 255                                 continue;
 256                             }
 257                         } else {
 258                             let second_last_i = interned_chars
 259                                 .next_back()
 260                                 .expect("we know we have at least three chars");
 261                             let second_last_e = existing_chars
 262                                 .next_back()
 263                                 .expect("we know we have at least three chars");
 264                             if !eq_or_numeric((second_last_i, second_last_e))
 265                                 || second_last_i == '_'
 266                                 || !interned_chars.zip(existing_chars).all(eq_or_numeric)
 267                             {
 268                                 // allowed similarity foo_x, foo_y
 269                                 // or too many chars differ (foo_x, boo_y) or (foox, booy)
 270                                 continue;
 271                             }
 272                             split_at = interned_name.char_indices().rev().next().map(|(i, _)| i);
 273                         }
 274                     } else {
 275                         let second_i = interned_chars.next().expect("we know we have at least two chars");
 276                         let second_e = existing_chars.next().expect("we know we have at least two chars");
 277                         if !eq_or_numeric((second_i, second_e))
 278                             || second_i == '_'
 279                             || !interned_chars.zip(existing_chars).all(eq_or_numeric)
 280                         {
 281                             // allowed similarity x_foo, y_foo
 282                             // or too many chars differ (x_foo, y_boo) or (xfoo, yboo)
 283                             continue;
 284                         }
 285                         split_at = interned_name.chars().next().map(char::len_utf8);
 286                     }
 287                 },
 288             }
 289             span_lint_and_then(
 290                 self.0.cx,
 291                 SIMILAR_NAMES,
 292                 ident.span,
 293                 "binding's name is too similar to existing binding",
 294                 |diag| {
 295                     diag.span_note(existing_name.span, "existing binding defined here");
 296                     if let Some(split) = split_at {
 297                         diag.span_help(
 298                             ident.span,
 299                             &format!(
 300                                 "separate the discriminating character by an \
 301                                  underscore like: `{}_{}`",
 302                                 &interned_name[..split],
 303                                 &interned_name[split..]
 304                             ),
 305                         );
 306                     }
 307                 },
 308             );
 309             return;
 310         }
 311         self.0.names.push(ExistingName {
 312             exemptions: get_exemptions(&interned_name).unwrap_or(&[]),
 313             interned: ident.name,
 314             span: ident.span,
 315             len: count,
 316         });
 317     }
 318 }
 319
 320 impl<'a, 'b> SimilarNamesLocalVisitor<'a, 'b> {
 321     /// ensure scoping rules work
 322     fn apply<F: for<'c> Fn(&'c mut Self)>(&mut self, f: F) {
 323         let n = self.names.len();
 324         let single_char_count = self.single_char_names.len();
 325         f(self);
 326         self.names.truncate(n);
 327         self.single_char_names.truncate(single_char_count);
 328     }
 329 }
 330
 331 impl<'a, 'tcx> Visitor<'tcx> for SimilarNamesLocalVisitor<'a, 'tcx> {
 332     fn visit_local(&mut self, local: &'tcx Local) {
 333         if let Some(ref init) = local.init {
 334             self.apply(|this| walk_expr(this, &**init));
 335         }
 336         // add the pattern after the expression because the bindings aren't available
 337         // yet in the init
 338         // expression
 339         SimilarNamesNameVisitor(self).visit_pat(&*local.pat);
 340     }
 341     fn visit_block(&mut self, blk: &'tcx Block) {
 342         self.single_char_names.push(vec![]);
 343
 344         self.apply(|this| walk_block(this, blk));
 345
 346         self.check_single_char_names();
 347         self.single_char_names.pop();
 348     }
 349     fn visit_arm(&mut self, arm: &'tcx Arm) {
 350         self.single_char_names.push(vec![]);
 351
 352         self.apply(|this| {
 353             SimilarNamesNameVisitor(this).visit_pat(&arm.pat);
 354             this.apply(|this| walk_expr(this, &arm.body));
 355         });
 356
 357         self.check_single_char_names();
 358         self.single_char_names.pop();
 359     }
 360     fn visit_item(&mut self, _: &Item) {
 361         // do not recurse into inner items
 362     }
 363 }
 364
 365 impl EarlyLintPass for NonExpressiveNames {
 366     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
 367         if in_external_macro(cx.sess, item.span) {
 368             return;
 369         }
 370
 371         if let ItemKind::Fn(box FnKind(_, ref sig, _, Some(ref blk))) = item.kind {
 372             do_check(self, cx, &item.attrs, &sig.decl, blk);
 373         }
 374     }
 375
 376     fn check_impl_item(&mut self, cx: &EarlyContext<'_>, item: &AssocItem) {
 377         if in_external_macro(cx.sess, item.span) {
 378             return;
 379         }
 380
 381         if let AssocItemKind::Fn(box FnKind(_, ref sig, _, Some(ref blk))) = item.kind {
 382             do_check(self, cx, &item.attrs, &sig.decl, blk);
 383         }
 384     }
 385 }
 386
 387 fn do_check(lint: &mut NonExpressiveNames, cx: &EarlyContext<'_>, attrs: &[Attribute], decl: &FnDecl, blk: &Block) {
 388     if !attrs.iter().any(|attr| attr.has_name(sym::test)) {
 389         let mut visitor = SimilarNamesLocalVisitor {
 390             names: Vec::new(),
 391             cx,
 392             lint,
 393             single_char_names: vec![vec![]],
 394         };
 395
 396         // initialize with function arguments
 397         for arg in &decl.inputs {
 398             SimilarNamesNameVisitor(&mut visitor).visit_pat(&arg.pat);
 399         }
 400         // walk all other bindings
 401         walk_block(&mut visitor, blk);
 402
 403         visitor.check_single_char_names();
 404     }
 405 }
 406
 407 /// Precondition: `a_name.chars().count() < b_name.chars().count()`.
 408 #[must_use]
 409 fn levenstein_not_1(a_name: &str, b_name: &str) -> bool {
 410     debug_assert!(a_name.chars().count() < b_name.chars().count());
 411     let mut a_chars = a_name.chars();
 412     let mut b_chars = b_name.chars();
 413     while let (Some(a), Some(b)) = (a_chars.next(), b_chars.next()) {
 414         if a == b {
 415             continue;
 416         }
 417         if let Some(b2) = b_chars.next() {
 418             // check if there's just one character inserted
 419             return a != b2 || a_chars.ne(b_chars);
 420         }
 421         // tuple
 422         // ntuple
 423         return true;
 424     }
 425     // for item in items
 426     true
 427 }