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         let count = interned_name.chars().count();
 203         if count < 3 {
 204             if count == 1 {
 205                 self.check_short_ident(ident);
 206             }
 207             return;
 208         }
 209         for existing_name in &self.0.names {
 210             if allowed_to_be_similar(&interned_name, existing_name.exemptions) {
 211                 continue;
 212             }
 213             let mut split_at = None;
 214             match existing_name.len.cmp(&count) {
 215                 Ordering::Greater => {
 216                     if existing_name.len - count != 1
 217                         || levenstein_not_1(&interned_name, &existing_name.interned.as_str())
 218                     {
 219                         continue;
 220                     }
 221                 },
 222                 Ordering::Less => {
 223                     if count - existing_name.len != 1
 224                         || levenstein_not_1(&existing_name.interned.as_str(), &interned_name)
 225                     {
 226                         continue;
 227                     }
 228                 },
 229                 Ordering::Equal => {
 230                     let mut interned_chars = interned_name.chars();
 231                     let interned_str = existing_name.interned.as_str();
 232                     let mut existing_chars = interned_str.chars();
 233                     let first_i = interned_chars.next().expect("we know we have at least one char");
 234                     let first_e = existing_chars.next().expect("we know we have at least one char");
 235                     let eq_or_numeric = |(a, b): (char, char)| a == b || a.is_numeric() && b.is_numeric();
 236
 237                     if eq_or_numeric((first_i, first_e)) {
 238                         let last_i = interned_chars.next_back().expect("we know we have at least two chars");
 239                         let last_e = existing_chars.next_back().expect("we know we have at least two chars");
 240                         if eq_or_numeric((last_i, last_e)) {
 241                             if interned_chars
 242                                 .zip(existing_chars)
 243                                 .filter(|&ie| !eq_or_numeric(ie))
 244                                 .count()
 245                                 != 1
 246                             {
 247                                 continue;
 248                             }
 249                         } else {
 250                             let second_last_i = interned_chars
 251                                 .next_back()
 252                                 .expect("we know we have at least three chars");
 253                             let second_last_e = existing_chars
 254                                 .next_back()
 255                                 .expect("we know we have at least three chars");
 256                             if !eq_or_numeric((second_last_i, second_last_e))
 257                                 || second_last_i == '_'
 258                                 || !interned_chars.zip(existing_chars).all(eq_or_numeric)
 259                             {
 260                                 // allowed similarity foo_x, foo_y
 261                                 // or too many chars differ (foo_x, boo_y) or (foox, booy)
 262                                 continue;
 263                             }
 264                             split_at = interned_name.char_indices().rev().next().map(|(i, _)| i);
 265                         }
 266                     } else {
 267                         let second_i = interned_chars.next().expect("we know we have at least two chars");
 268                         let second_e = existing_chars.next().expect("we know we have at least two chars");
 269                         if !eq_or_numeric((second_i, second_e))
 270                             || second_i == '_'
 271                             || !interned_chars.zip(existing_chars).all(eq_or_numeric)
 272                         {
 273                             // allowed similarity x_foo, y_foo
 274                             // or too many chars differ (x_foo, y_boo) or (xfoo, yboo)
 275                             continue;
 276                         }
 277                         split_at = interned_name.chars().next().map(char::len_utf8);
 278                     }
 279                 },
 280             }
 281             span_lint_and_then(
 282                 self.0.cx,
 283                 SIMILAR_NAMES,
 284                 ident.span,
 285                 "binding's name is too similar to existing binding",
 286                 |diag| {
 287                     diag.span_note(existing_name.span, "existing binding defined here");
 288                     if let Some(split) = split_at {
 289                         diag.span_help(
 290                             ident.span,
 291                             &format!(
 292                                 "separate the discriminating character by an \
 293                                  underscore like: `{}_{}`",
 294                                 &interned_name[..split],
 295                                 &interned_name[split..]
 296                             ),
 297                         );
 298                     }
 299                 },
 300             );
 301             return;
 302         }
 303         self.0.names.push(ExistingName {
 304             exemptions: get_exemptions(&interned_name).unwrap_or(&[]),
 305             interned: ident.name,
 306             span: ident.span,
 307             len: count,
 308         });
 309     }
 310 }
 311
 312 impl<'a, 'b> SimilarNamesLocalVisitor<'a, 'b> {
 313     /// ensure scoping rules work
 314     fn apply<F: for<'c> Fn(&'c mut Self)>(&mut self, f: F) {
 315         let n = self.names.len();
 316         let single_char_count = self.single_char_names.len();
 317         f(self);
 318         self.names.truncate(n);
 319         self.single_char_names.truncate(single_char_count);
 320     }
 321 }
 322
 323 impl<'a, 'tcx> Visitor<'tcx> for SimilarNamesLocalVisitor<'a, 'tcx> {
 324     fn visit_local(&mut self, local: &'tcx Local) {
 325         if let Some(ref init) = local.init {
 326             self.apply(|this| walk_expr(this, &**init));
 327         }
 328         // add the pattern after the expression because the bindings aren't available
 329         // yet in the init
 330         // expression
 331         SimilarNamesNameVisitor(self).visit_pat(&*local.pat);
 332     }
 333     fn visit_block(&mut self, blk: &'tcx Block) {
 334         self.single_char_names.push(vec![]);
 335
 336         self.apply(|this| walk_block(this, blk));
 337
 338         self.check_single_char_names();
 339         self.single_char_names.pop();
 340     }
 341     fn visit_arm(&mut self, arm: &'tcx Arm) {
 342         self.single_char_names.push(vec![]);
 343
 344         self.apply(|this| {
 345             SimilarNamesNameVisitor(this).visit_pat(&arm.pat);
 346             this.apply(|this| walk_expr(this, &arm.body));
 347         });
 348
 349         self.check_single_char_names();
 350         self.single_char_names.pop();
 351     }
 352     fn visit_item(&mut self, _: &Item) {
 353         // do not recurse into inner items
 354     }
 355 }
 356
 357 impl EarlyLintPass for NonExpressiveNames {
 358     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
 359         if in_external_macro(cx.sess, item.span) {
 360             return;
 361         }
 362
 363         if let ItemKind::Fn(_, ref sig, _, Some(ref blk)) = item.kind {
 364             do_check(self, cx, &item.attrs, &sig.decl, blk);
 365         }
 366     }
 367
 368     fn check_impl_item(&mut self, cx: &EarlyContext<'_>, item: &AssocItem) {
 369         if in_external_macro(cx.sess, item.span) {
 370             return;
 371         }
 372
 373         if let AssocItemKind::Fn(_, ref sig, _, Some(ref blk)) = item.kind {
 374             do_check(self, cx, &item.attrs, &sig.decl, blk);
 375         }
 376     }
 377 }
 378
 379 fn do_check(lint: &mut NonExpressiveNames, cx: &EarlyContext<'_>, attrs: &[Attribute], decl: &FnDecl, blk: &Block) {
 380     if !attrs.iter().any(|attr| attr.has_name(sym::test)) {
 381         let mut visitor = SimilarNamesLocalVisitor {
 382             names: Vec::new(),
 383             cx,
 384             lint,
 385             single_char_names: vec![vec![]],
 386         };
 387
 388         // initialize with function arguments
 389         for arg in &decl.inputs {
 390             SimilarNamesNameVisitor(&mut visitor).visit_pat(&arg.pat);
 391         }
 392         // walk all other bindings
 393         walk_block(&mut visitor, blk);
 394
 395         visitor.check_single_char_names();
 396     }
 397 }
 398
 399 /// Precondition: `a_name.chars().count() < b_name.chars().count()`.
 400 #[must_use]
 401 fn levenstein_not_1(a_name: &str, b_name: &str) -> bool {
 402     debug_assert!(a_name.chars().count() < b_name.chars().count());
 403     let mut a_chars = a_name.chars();
 404     let mut b_chars = b_name.chars();
 405     while let (Some(a), Some(b)) = (a_chars.next(), b_chars.next()) {
 406         if a == b {
 407             continue;
 408         }
 409         if let Some(b2) = b_chars.next() {
 410             // check if there's just one character inserted
 411             return a != b2 || a_chars.ne(b_chars);
 412         } else {
 413             // tuple
 414             // ntuple
 415             return true;
 416         }
 417     }
 418     // for item in items
 419     true
 420 }