src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs

   1 #![allow(clippy::wildcard_imports, clippy::enum_glob_use)]
   2
   3 use clippy_utils::ast_utils::{eq_field_pat, eq_id, eq_maybe_qself, eq_pat, eq_path};
   4 use clippy_utils::diagnostics::span_lint_and_then;
   5 use clippy_utils::{meets_msrv, msrvs, over};
   6 use rustc_ast::mut_visit::*;
   7 use rustc_ast::ptr::P;
   8 use rustc_ast::{self as ast, Pat, PatKind, PatKind::*, DUMMY_NODE_ID};
   9 use rustc_ast_pretty::pprust;
  10 use rustc_errors::Applicability;
  11 use rustc_lint::{EarlyContext, EarlyLintPass};
  12 use rustc_semver::RustcVersion;
  13 use rustc_session::{declare_tool_lint, impl_lint_pass};
  14 use rustc_span::DUMMY_SP;
  15
  16 use std::cell::Cell;
  17 use std::mem;
  18
  19 declare_clippy_lint! {
  20     /// **What it does:**
  21     ///
  22     /// Checks for unnested or-patterns, e.g., `Some(0) | Some(2)` and
  23     /// suggests replacing the pattern with a nested one, `Some(0 | 2)`.
  24     ///
  25     /// Another way to think of this is that it rewrites patterns in
  26     /// *disjunctive normal form (DNF)* into *conjunctive normal form (CNF)*.
  27     ///
  28     /// **Why is this bad?**
  29     ///
  30     /// In the example above, `Some` is repeated, which unncessarily complicates the pattern.
  31     ///
  32     /// **Known problems:** None.
  33     ///
  34     /// **Example:**
  35     ///
  36     /// ```rust
  37     /// fn main() {
  38     ///     if let Some(0) | Some(2) = Some(0) {}
  39     /// }
  40     /// ```
  41     /// Use instead:
  42     /// ```rust
  43     /// #![feature(or_patterns)]
  44     ///
  45     /// fn main() {
  46     ///     if let Some(0 | 2) = Some(0) {}
  47     /// }
  48     /// ```
  49     pub UNNESTED_OR_PATTERNS,
  50     pedantic,
  51     "unnested or-patterns, e.g., `Foo(Bar) | Foo(Baz) instead of `Foo(Bar | Baz)`"
  52 }
  53
  54 #[derive(Clone, Copy)]
  55 pub struct UnnestedOrPatterns {
  56     msrv: Option<RustcVersion>,
  57 }
  58
  59 impl UnnestedOrPatterns {
  60     #[must_use]
  61     pub fn new(msrv: Option<RustcVersion>) -> Self {
  62         Self { msrv }
  63     }
  64 }
  65
  66 impl_lint_pass!(UnnestedOrPatterns => [UNNESTED_OR_PATTERNS]);
  67
  68 impl EarlyLintPass for UnnestedOrPatterns {
  69     fn check_arm(&mut self, cx: &EarlyContext<'_>, a: &ast::Arm) {
  70         if meets_msrv(self.msrv.as_ref(), &msrvs::OR_PATTERNS) {
  71             lint_unnested_or_patterns(cx, &a.pat);
  72         }
  73     }
  74
  75     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
  76         if meets_msrv(self.msrv.as_ref(), &msrvs::OR_PATTERNS) {
  77             if let ast::ExprKind::Let(pat, _) = &e.kind {
  78                 lint_unnested_or_patterns(cx, pat);
  79             }
  80         }
  81     }
  82
  83     fn check_param(&mut self, cx: &EarlyContext<'_>, p: &ast::Param) {
  84         if meets_msrv(self.msrv.as_ref(), &msrvs::OR_PATTERNS) {
  85             lint_unnested_or_patterns(cx, &p.pat);
  86         }
  87     }
  88
  89     fn check_local(&mut self, cx: &EarlyContext<'_>, l: &ast::Local) {
  90         if meets_msrv(self.msrv.as_ref(), &msrvs::OR_PATTERNS) {
  91             lint_unnested_or_patterns(cx, &l.pat);
  92         }
  93     }
  94
  95     extract_msrv_attr!(EarlyContext);
  96 }
  97
  98 fn lint_unnested_or_patterns(cx: &EarlyContext<'_>, pat: &Pat) {
  99     if let Ident(.., None) | Lit(_) | Wild | Path(..) | Range(..) | Rest | MacCall(_) = pat.kind {
 100         // This is a leaf pattern, so cloning is unprofitable.
 101         return;
 102     }
 103
 104     let mut pat = P(pat.clone());
 105
 106     // Nix all the paren patterns everywhere so that they aren't in our way.
 107     remove_all_parens(&mut pat);
 108
 109     // Transform all unnested or-patterns into nested ones, and if there were none, quit.
 110     if !unnest_or_patterns(&mut pat) {
 111         return;
 112     }
 113
 114     span_lint_and_then(cx, UNNESTED_OR_PATTERNS, pat.span, "unnested or-patterns", |db| {
 115         insert_necessary_parens(&mut pat);
 116         db.span_suggestion_verbose(
 117             pat.span,
 118             "nest the patterns",
 119             pprust::pat_to_string(&pat),
 120             Applicability::MachineApplicable,
 121         );
 122     });
 123 }
 124
 125 /// Remove all `(p)` patterns in `pat`.
 126 fn remove_all_parens(pat: &mut P<Pat>) {
 127     struct Visitor;
 128     impl MutVisitor for Visitor {
 129         fn visit_pat(&mut self, pat: &mut P<Pat>) {
 130             noop_visit_pat(pat, self);
 131             let inner = match &mut pat.kind {
 132                 Paren(i) => mem::replace(&mut i.kind, Wild),
 133                 _ => return,
 134             };
 135             pat.kind = inner;
 136         }
 137     }
 138     Visitor.visit_pat(pat);
 139 }
 140
 141 /// Insert parens where necessary according to Rust's precedence rules for patterns.
 142 fn insert_necessary_parens(pat: &mut P<Pat>) {
 143     struct Visitor;
 144     impl MutVisitor for Visitor {
 145         fn visit_pat(&mut self, pat: &mut P<Pat>) {
 146             use ast::{BindingMode::*, Mutability::*};
 147             noop_visit_pat(pat, self);
 148             let target = match &mut pat.kind {
 149                 // `i @ a | b`, `box a | b`, and `& mut? a | b`.
 150                 Ident(.., Some(p)) | Box(p) | Ref(p, _) if matches!(&p.kind, Or(ps) if ps.len() > 1) => p,
 151                 Ref(p, Not) if matches!(p.kind, Ident(ByValue(Mut), ..)) => p, // `&(mut x)`
 152                 _ => return,
 153             };
 154             target.kind = Paren(P(take_pat(target)));
 155         }
 156     }
 157     Visitor.visit_pat(pat);
 158 }
 159
 160 /// Unnest or-patterns `p0 | ... | p1` in the pattern `pat`.
 161 /// For example, this would transform `Some(0) | FOO | Some(2)` into `Some(0 | 2) | FOO`.
 162 fn unnest_or_patterns(pat: &mut P<Pat>) -> bool {
 163     struct Visitor {
 164         changed: bool,
 165     }
 166     impl MutVisitor for Visitor {
 167         fn visit_pat(&mut self, p: &mut P<Pat>) {
 168             // This is a bottom up transformation, so recurse first.
 169             noop_visit_pat(p, self);
 170
 171             // Don't have an or-pattern? Just quit early on.
 172             let alternatives = match &mut p.kind {
 173                 Or(ps) => ps,
 174                 _ => return,
 175             };
 176
 177             // Collapse or-patterns directly nested in or-patterns.
 178             let mut idx = 0;
 179             let mut this_level_changed = false;
 180             while idx < alternatives.len() {
 181                 let inner = if let Or(ps) = &mut alternatives[idx].kind {
 182                     mem::take(ps)
 183                 } else {
 184                     idx += 1;
 185                     continue;
 186                 };
 187                 this_level_changed = true;
 188                 alternatives.splice(idx..=idx, inner);
 189             }
 190
 191             // Focus on `p_n` and then try to transform all `p_i` where `i > n`.
 192             let mut focus_idx = 0;
 193             while focus_idx < alternatives.len() {
 194                 this_level_changed |= transform_with_focus_on_idx(alternatives, focus_idx);
 195                 focus_idx += 1;
 196             }
 197             self.changed |= this_level_changed;
 198
 199             // Deal with `Some(Some(0)) | Some(Some(1))`.
 200             if this_level_changed {
 201                 noop_visit_pat(p, self);
 202             }
 203         }
 204     }
 205
 206     let mut visitor = Visitor { changed: false };
 207     visitor.visit_pat(pat);
 208     visitor.changed
 209 }
 210
 211 /// Match `$scrutinee` against `$pat` and extract `$then` from it.
 212 /// Panics if there is no match.
 213 macro_rules! always_pat {
 214     ($scrutinee:expr, $pat:pat => $then:expr) => {
 215         match $scrutinee {
 216             $pat => $then,
 217             _ => unreachable!(),
 218         }
 219     };
 220 }
 221
 222 /// Focus on `focus_idx` in `alternatives`,
 223 /// attempting to extend it with elements of the same constructor `C`
 224 /// in `alternatives[focus_idx + 1..]`.
 225 fn transform_with_focus_on_idx(alternatives: &mut Vec<P<Pat>>, focus_idx: usize) -> bool {
 226     // Extract the kind; we'll need to make some changes in it.
 227     let mut focus_kind = mem::replace(&mut alternatives[focus_idx].kind, PatKind::Wild);
 228     // We'll focus on `alternatives[focus_idx]`,
 229     // so we're draining from `alternatives[focus_idx + 1..]`.
 230     let start = focus_idx + 1;
 231
 232     // We're trying to find whatever kind (~"constructor") we found in `alternatives[start..]`.
 233     let changed = match &mut focus_kind {
 234         // These pattern forms are "leafs" and do not have sub-patterns.
 235         // Therefore they are not some form of constructor `C`,
 236         // with which a pattern `C(p_0)` may be formed,
 237         // which we would want to join with other `C(p_j)`s.
 238         Ident(.., None) | Lit(_) | Wild | Path(..) | Range(..) | Rest | MacCall(_)
 239         // Dealt with elsewhere.
 240         | Or(_) | Paren(_) => false,
 241         // Transform `box x | ... | box y` into `box (x | y)`.
 242         //
 243         // The cases below until `Slice(...)` deal with *singleton* products.
 244         // These patterns have the shape `C(p)`, and not e.g., `C(p0, ..., pn)`.
 245         Box(target) => extend_with_matching(
 246             target, start, alternatives,
 247             |k| matches!(k, Box(_)),
 248             |k| always_pat!(k, Box(p) => p),
 249         ),
 250         // Transform `&m x | ... | &m y` into `&m (x | y)`.
 251         Ref(target, m1) => extend_with_matching(
 252             target, start, alternatives,
 253             |k| matches!(k, Ref(_, m2) if m1 == m2), // Mutabilities must match.
 254             |k| always_pat!(k, Ref(p, _) => p),
 255         ),
 256         // Transform `b @ p0 | ... b @ p1` into `b @ (p0 | p1)`.
 257         Ident(b1, i1, Some(target)) => extend_with_matching(
 258             target, start, alternatives,
 259             // Binding names must match.
 260             |k| matches!(k, Ident(b2, i2, Some(_)) if b1 == b2 && eq_id(*i1, *i2)),
 261             |k| always_pat!(k, Ident(_, _, Some(p)) => p),
 262         ),
 263         // Transform `[pre, x, post] | ... | [pre, y, post]` into `[pre, x | y, post]`.
 264         Slice(ps1) => extend_with_matching_product(
 265             ps1, start, alternatives,
 266             |k, ps1, idx| matches!(k, Slice(ps2) if eq_pre_post(ps1, ps2, idx)),
 267             |k| always_pat!(k, Slice(ps) => ps),
 268         ),
 269         // Transform `(pre, x, post) | ... | (pre, y, post)` into `(pre, x | y, post)`.
 270         Tuple(ps1) => extend_with_matching_product(
 271             ps1, start, alternatives,
 272             |k, ps1, idx| matches!(k, Tuple(ps2) if eq_pre_post(ps1, ps2, idx)),
 273             |k| always_pat!(k, Tuple(ps) => ps),
 274         ),
 275         // Transform `S(pre, x, post) | ... | S(pre, y, post)` into `S(pre, x | y, post)`.
 276         TupleStruct(qself1, path1, ps1) => extend_with_matching_product(
 277             ps1, start, alternatives,
 278             |k, ps1, idx| matches!(
 279                 k,
 280                 TupleStruct(qself2, path2, ps2)
 281                     if eq_maybe_qself(qself1, qself2) && eq_path(path1, path2) && eq_pre_post(ps1, ps2, idx)
 282             ),
 283             |k| always_pat!(k, TupleStruct(_, _, ps) => ps),
 284         ),
 285         // Transform a record pattern `S { fp_0, ..., fp_n }`.
 286         Struct(qself1, path1, fps1, rest1) => extend_with_struct_pat(qself1, path1, fps1, *rest1, start, alternatives),
 287     };
 288
 289     alternatives[focus_idx].kind = focus_kind;
 290     changed
 291 }
 292
 293 /// Here we focusing on a record pattern `S { fp_0, ..., fp_n }`.
 294 /// In particular, for a record pattern, the order in which the field patterns is irrelevant.
 295 /// So when we fixate on some `ident_k: pat_k`, we try to find `ident_k` in the other pattern
 296 /// and check that all `fp_i` where `i ∈ ((0...n) \ k)` between two patterns are equal.
 297 fn extend_with_struct_pat(
 298     qself1: &Option<ast::QSelf>,
 299     path1: &ast::Path,
 300     fps1: &mut Vec<ast::PatField>,
 301     rest1: bool,
 302     start: usize,
 303     alternatives: &mut Vec<P<Pat>>,
 304 ) -> bool {
 305     (0..fps1.len()).any(|idx| {
 306         let pos_in_2 = Cell::new(None); // The element `k`.
 307         let tail_or = drain_matching(
 308             start,
 309             alternatives,
 310             |k| {
 311                 matches!(k, Struct(qself2, path2, fps2, rest2)
 312                 if rest1 == *rest2 // If one struct pattern has `..` so must the other.
 313                 && eq_maybe_qself(qself1, qself2)
 314                 && eq_path(path1, path2)
 315                 && fps1.len() == fps2.len()
 316                 && fps1.iter().enumerate().all(|(idx_1, fp1)| {
 317                     if idx_1 == idx {
 318                         // In the case of `k`, we merely require identical field names
 319                         // so that we will transform into `ident_k: p1_k | p2_k`.
 320                         let pos = fps2.iter().position(|fp2| eq_id(fp1.ident, fp2.ident));
 321                         pos_in_2.set(pos);
 322                         pos.is_some()
 323                     } else {
 324                         fps2.iter().any(|fp2| eq_field_pat(fp1, fp2))
 325                     }
 326                 }))
 327             },
 328             // Extract `p2_k`.
 329             |k| always_pat!(k, Struct(_, _, mut fps, _) => fps.swap_remove(pos_in_2.take().unwrap()).pat),
 330         );
 331         extend_with_tail_or(&mut fps1[idx].pat, tail_or)
 332     })
 333 }
 334
 335 /// Like `extend_with_matching` but for products with > 1 factor, e.g., `C(p_0, ..., p_n)`.
 336 /// Here, the idea is that we fixate on some `p_k` in `C`,
 337 /// allowing it to vary between two `targets` and `ps2` (returned by `extract`),
 338 /// while also requiring `ps1[..n] ~ ps2[..n]` (pre) and `ps1[n + 1..] ~ ps2[n + 1..]` (post),
 339 /// where `~` denotes semantic equality.
 340 fn extend_with_matching_product(
 341     targets: &mut Vec<P<Pat>>,
 342     start: usize,
 343     alternatives: &mut Vec<P<Pat>>,
 344     predicate: impl Fn(&PatKind, &[P<Pat>], usize) -> bool,
 345     extract: impl Fn(PatKind) -> Vec<P<Pat>>,
 346 ) -> bool {
 347     (0..targets.len()).any(|idx| {
 348         let tail_or = drain_matching(
 349             start,
 350             alternatives,
 351             |k| predicate(k, targets, idx),
 352             |k| extract(k).swap_remove(idx),
 353         );
 354         extend_with_tail_or(&mut targets[idx], tail_or)
 355     })
 356 }
 357
 358 /// Extract the pattern from the given one and replace it with `Wild`.
 359 /// This is meant for temporarily swapping out the pattern for manipulation.
 360 fn take_pat(from: &mut Pat) -> Pat {
 361     let dummy = Pat {
 362         id: DUMMY_NODE_ID,
 363         kind: Wild,
 364         span: DUMMY_SP,
 365         tokens: None,
 366     };
 367     mem::replace(from, dummy)
 368 }
 369
 370 /// Extend `target` as an or-pattern with the alternatives
 371 /// in `tail_or` if there are any and return if there were.
 372 fn extend_with_tail_or(target: &mut Pat, tail_or: Vec<P<Pat>>) -> bool {
 373     fn extend(target: &mut Pat, mut tail_or: Vec<P<Pat>>) {
 374         match target {
 375             // On an existing or-pattern in the target, append to it.
 376             Pat { kind: Or(ps), .. } => ps.append(&mut tail_or),
 377             // Otherwise convert the target to an or-pattern.
 378             target => {
 379                 let mut init_or = vec![P(take_pat(target))];
 380                 init_or.append(&mut tail_or);
 381                 target.kind = Or(init_or);
 382             },
 383         }
 384     }
 385
 386     let changed = !tail_or.is_empty();
 387     if changed {
 388         // Extend the target.
 389         extend(target, tail_or);
 390     }
 391     changed
 392 }
 393
 394 // Extract all inner patterns in `alternatives` matching our `predicate`.
 395 // Only elements beginning with `start` are considered for extraction.
 396 fn drain_matching(
 397     start: usize,
 398     alternatives: &mut Vec<P<Pat>>,
 399     predicate: impl Fn(&PatKind) -> bool,
 400     extract: impl Fn(PatKind) -> P<Pat>,
 401 ) -> Vec<P<Pat>> {
 402     let mut tail_or = vec![];
 403     let mut idx = 0;
 404     for pat in alternatives.drain_filter(|p| {
 405         // Check if we should extract, but only if `idx >= start`.
 406         idx += 1;
 407         idx > start && predicate(&p.kind)
 408     }) {
 409         tail_or.push(extract(pat.into_inner().kind));
 410     }
 411     tail_or
 412 }
 413
 414 fn extend_with_matching(
 415     target: &mut Pat,
 416     start: usize,
 417     alternatives: &mut Vec<P<Pat>>,
 418     predicate: impl Fn(&PatKind) -> bool,
 419     extract: impl Fn(PatKind) -> P<Pat>,
 420 ) -> bool {
 421     extend_with_tail_or(target, drain_matching(start, alternatives, predicate, extract))
 422 }
 423
 424 /// Are the patterns in `ps1` and `ps2` equal save for `ps1[idx]` compared to `ps2[idx]`?
 425 fn eq_pre_post(ps1: &[P<Pat>], ps2: &[P<Pat>], idx: usize) -> bool {
 426     ps1.len() == ps2.len()
 427         && ps1[idx].is_rest() == ps2[idx].is_rest() // Avoid `[x, ..] | [x, 0]` => `[x, .. | 0]`.
 428         && over(&ps1[..idx], &ps2[..idx], |l, r| eq_pat(l, r))
 429         && over(&ps1[idx + 1..], &ps2[idx + 1..], |l, r| eq_pat(l, r))
 430 }