clippy_lints/src/non_expressive_names.rs

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