Auto merge of rust-lang#61708 - dlrobertson:or-patterns-0, r=centril

Initial implementation of or-patterns

An incomplete implementation of or-patterns (e.g. `Some(0 | 1)` as a pattern). This patch set aims to implement initial parsing of `or-patterns`.

Related to: rust-lang#54883

CC @alexreg @varkor
r? @Centril

src/doc/unstable-book/src/language-features/or-patterns.md

@@ -0,0 +1,36 @@
+# `or_patterns`
+
+The tracking issue for this feature is: [#54883]
+
+[#54883]: https://github.com/rust-lang/rust/issues/54883
+
+------------------------
+
+The `or_pattern` language feature allows `|` to be arbitrarily nested within
+a pattern, for example, `Some(A(0) | B(1 | 2))` becomes a valid pattern.
+
+## Examples
+
+```rust,ignore
+#![feature(or_patterns)]
+
+pub enum Foo {
+    Bar,
+    Baz,
+    Quux,
+}
+
+pub fn example(maybe_foo: Option<Foo>) {
+    match maybe_foo {
+        Some(Foo::Bar | Foo::Baz) => {
+            println!("The value contained `Bar` or `Baz`");
+        }
+        Some(_) => {
+            println!("The value did not contain `Bar` or `Baz`");
+        }
+        None => {
+            println!("The value was `None`");
+        }
+    }
+}
+```

src/librustc/cfg/construct.rs

@@ -140,6 +140,11 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
                 self.add_ast_node(pat.hir_id.local_id, &[pats_exit])
             }
 
+            PatKind::Or(ref pats) => {
+                let branches: Vec<_> = pats.iter().map(|p| self.pat(p, pred)).collect();
+                self.add_ast_node(pat.hir_id.local_id, &branches)
+            }
+
             PatKind::Slice(ref pre, ref vec, ref post) => {
                 let pre_exit = self.pats_all(pre.iter(), pred);
                 let vec_exit = self.pats_all(vec.iter(), pre_exit);

src/librustc/hir/intravisit.rs

@@ -709,6 +709,7 @@ pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat) {
                 visitor.visit_pat(&field.pat)
             }
         }
+        PatKind::Or(ref pats) => walk_list!(visitor, visit_pat, pats),
         PatKind::Tuple(ref tuple_elements, _) => {
             walk_list!(visitor, visit_pat, tuple_elements);
         }

src/librustc/hir/lowering.rs

@@ -2669,6 +2669,9 @@ impl<'a> LoweringContext<'a> {
                 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
                 hir::PatKind::TupleStruct(qpath, pats, ddpos)
             }
+            PatKind::Or(ref pats) => {
+                hir::PatKind::Or(pats.iter().map(|x| self.lower_pat(x)).collect())
+            }
             PatKind::Path(ref qself, ref path) => {
                 let qpath = self.lower_qpath(
                     p.id,

src/librustc/hir/mod.rs

@@ -881,6 +881,7 @@ impl Pat {
             PatKind::TupleStruct(_, ref s, _) | PatKind::Tuple(ref s, _) => {
                 s.iter().all(|p| p.walk_(it))
             }
+            PatKind::Or(ref pats) => pats.iter().all(|p| p.walk_(it)),
             PatKind::Box(ref s) | PatKind::Ref(ref s, _) => {
                 s.walk_(it)
             }
@@ -975,6 +976,10 @@ pub enum PatKind {
     /// `0 <= position <= subpats.len()`
     TupleStruct(QPath, HirVec<P<Pat>>, Option<usize>),
 
+    /// An or-pattern `A | B | C`.
+    /// Invariant: `pats.len() >= 2`.
+    Or(HirVec<P<Pat>>),
+
     /// A path pattern for an unit struct/variant or a (maybe-associated) constant.
     Path(QPath),
 

src/librustc/hir/print.rs

@@ -1687,6 +1687,9 @@ impl<'a> State<'a> {
                 self.s.space();
                 self.s.word("}");
             }
+            PatKind::Or(ref pats) => {
+                self.strsep("|", true, Inconsistent, &pats[..], |s, p| s.print_pat(&p));
+            }
             PatKind::Tuple(ref elts, ddpos) => {
                 self.popen();
                 if let Some(ddpos) = ddpos {

src/librustc/middle/mem_categorization.rs

@@ -1290,6 +1290,12 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
                 }
             }
 
+            PatKind::Or(ref pats) => {
+                for pat in pats {
+                    self.cat_pattern_(cmt.clone(), &pat, op)?;
+                }
+            }
+
             PatKind::Binding(.., Some(ref subpat)) => {
                 self.cat_pattern_(cmt, &subpat, op)?;
             }

src/librustc_mir/build/matches/mod.rs

@@ -657,6 +657,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     self.visit_bindings(&subpattern.pattern, subpattern_user_ty, f);
                 }
             }
+            PatternKind::Or { ref pats } => {
+                for pat in pats {
+                    self.visit_bindings(&pat, pattern_user_ty.clone(), f);
+                }
+            }
         }
     }
 }

src/librustc_mir/build/matches/simplify.rs

@@ -195,6 +195,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 candidate.match_pairs.push(MatchPair::new(place, subpattern));
                 Ok(())
             }
+
+            PatternKind::Or { .. } => {
+                Err(match_pair)
+            }
         }
     }
 }

src/librustc_mir/build/matches/test.rs

@@ -87,6 +87,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             PatternKind::AscribeUserType { .. } |
             PatternKind::Array { .. } |
             PatternKind::Wild |
+            PatternKind::Or { .. } |
             PatternKind::Binding { .. } |
             PatternKind::Leaf { .. } |
             PatternKind::Deref { .. } => {
@@ -130,6 +131,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             PatternKind::Slice { .. } |
             PatternKind::Array { .. } |
             PatternKind::Wild |
+            PatternKind::Or { .. } |
             PatternKind::Binding { .. } |
             PatternKind::AscribeUserType { .. } |
             PatternKind::Leaf { .. } |

src/librustc_mir/hair/pattern/_match.rs

@@ -1359,6 +1359,9 @@ fn pat_constructors<'tcx>(cx: &mut MatchCheckCtxt<'_, 'tcx>,
                 Some(vec![Slice(pat_len)])
             }
         }
+        PatternKind::Or { .. } => {
+            bug!("support for or-patterns has not been fully implemented yet.");
+        }
     }
 }
 
@@ -1884,6 +1887,10 @@ fn specialize<'p, 'a: 'p, 'tcx>(
                     "unexpected ctor {:?} for slice pat", constructor)
             }
         }
+
+        PatternKind::Or { .. } => {
+            bug!("support for or-patterns has not been fully implemented yet.");
+        }
     };
     debug!("specialize({:#?}, {:#?}) = {:#?}", r[0], wild_patterns, head);
 

src/librustc_mir/hair/pattern/mod.rs

@@ -175,6 +175,12 @@ pub enum PatternKind<'tcx> {
         slice: Option<Pattern<'tcx>>,
         suffix: Vec<Pattern<'tcx>>,
     },
+
+    /// An or-pattern, e.g. `p | q`.
+    /// Invariant: `pats.len() >= 2`.
+    Or {
+        pats: Vec<Pattern<'tcx>>,
+    },
 }
 
 #[derive(Copy, Clone, Debug, PartialEq)]
@@ -186,6 +192,18 @@ pub struct PatternRange<'tcx> {
 
 impl<'tcx> fmt::Display for Pattern<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Printing lists is a chore.
+        let mut first = true;
+        let mut start_or_continue = |s| {
+            if first {
+                first = false;
+                ""
+            } else {
+                s
+            }
+        };
+        let mut start_or_comma = || start_or_continue(", ");
+
         match *self.kind {
             PatternKind::Wild => write!(f, "_"),
             PatternKind::AscribeUserType { ref subpattern, .. } =>
@@ -224,9 +242,6 @@ impl<'tcx> fmt::Display for Pattern<'tcx> {
                     }
                 };
 
-                let mut first = true;
-                let mut start_or_continue = || if first { first = false; "" } else { ", " };
-
                 if let Some(variant) = variant {
                     write!(f, "{}", variant.ident)?;
 
@@ -241,12 +256,12 @@ impl<'tcx> fmt::Display for Pattern<'tcx> {
                                 continue;
                             }
                             let name = variant.fields[p.field.index()].ident;
-                            write!(f, "{}{}: {}", start_or_continue(), name, p.pattern)?;
+                            write!(f, "{}{}: {}", start_or_comma(), name, p.pattern)?;
                             printed += 1;
                         }
 
                         if printed < variant.fields.len() {
-                            write!(f, "{}..", start_or_continue())?;
+                            write!(f, "{}..", start_or_comma())?;
                         }
 
                         return write!(f, " }}");
@@ -257,7 +272,7 @@ impl<'tcx> fmt::Display for Pattern<'tcx> {
                 if num_fields != 0 || variant.is_none() {
                     write!(f, "(")?;
                     for i in 0..num_fields {
-                        write!(f, "{}", start_or_continue())?;
+                        write!(f, "{}", start_or_comma())?;
 
                         // Common case: the field is where we expect it.
                         if let Some(p) = subpatterns.get(i) {
@@ -305,25 +320,29 @@ impl<'tcx> fmt::Display for Pattern<'tcx> {
             }
             PatternKind::Slice { ref prefix, ref slice, ref suffix } |
             PatternKind::Array { ref prefix, ref slice, ref suffix } => {
-                let mut first = true;
-                let mut start_or_continue = || if first { first = false; "" } else { ", " };
                 write!(f, "[")?;
                 for p in prefix {
-                    write!(f, "{}{}", start_or_continue(), p)?;
+                    write!(f, "{}{}", start_or_comma(), p)?;
                 }
                 if let Some(ref slice) = *slice {
-                    write!(f, "{}", start_or_continue())?;
+                    write!(f, "{}", start_or_comma())?;
                     match *slice.kind {
                         PatternKind::Wild => {}
                         _ => write!(f, "{}", slice)?
                     }
                     write!(f, "..")?;
                 }
                 for p in suffix {
-                    write!(f, "{}{}", start_or_continue(), p)?;
+                    write!(f, "{}{}", start_or_comma(), p)?;
                 }
                 write!(f, "]")
             }
+            PatternKind::Or { ref pats } => {
+                for pat in pats {
+                    write!(f, "{}{}", start_or_continue(" | "), pat)?;
+                }
+                Ok(())
+            }
         }
     }
 }
@@ -655,6 +674,12 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> {
 
                 self.lower_variant_or_leaf(res, pat.hir_id, pat.span, ty, subpatterns)
             }
+
+            PatKind::Or(ref pats) => {
+                PatternKind::Or {
+                    pats: pats.iter().map(|p| self.lower_pattern(p)).collect(),
+                }
+            }
         };
 
         Pattern {
@@ -1436,6 +1461,7 @@ impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
                 slice: slice.fold_with(folder),
                 suffix: suffix.fold_with(folder)
             },
+            PatternKind::Or { ref pats } => PatternKind::Or { pats: pats.fold_with(folder) },
         }
     }
 }

src/librustc_typeck/check/_match.rs

@@ -53,6 +53,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let is_non_ref_pat = match pat.node {
             PatKind::Struct(..) |
             PatKind::TupleStruct(..) |
+            PatKind::Or(_) |
             PatKind::Tuple(..) |
             PatKind::Box(_) |
             PatKind::Range(..) |
@@ -309,6 +310,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             PatKind::Struct(ref qpath, ref fields, etc) => {
                 self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, discrim_span)
             }
+            PatKind::Or(ref pats) => {
+                let expected_ty = self.structurally_resolved_type(pat.span, expected);
+                for pat in pats {
+                    self.check_pat_walk(pat, expected, def_bm, discrim_span);
+                }
+                expected_ty
+            }
             PatKind::Tuple(ref elements, ddpos) => {
                 let mut expected_len = elements.len();
                 if ddpos.is_some() {

src/librustdoc/clean/mod.rs

@@ -4107,6 +4107,9 @@ fn name_from_pat(p: &hir::Pat) -> String {
                 if etc { ", .." } else { "" }
             )
         }
+        PatKind::Or(ref pats) => {
+            pats.iter().map(|p| name_from_pat(&**p)).collect::<Vec<String>>().join(" | ")
+        }
         PatKind::Tuple(ref elts, _) => format!("({})", elts.iter().map(|p| name_from_pat(&**p))
                                             .collect::<Vec<String>>().join(", ")),
         PatKind::Box(ref p) => name_from_pat(&**p),

src/libsyntax/ast.rs

@@ -572,9 +572,10 @@ impl Pat {
         match &self.node {
             PatKind::Ident(_, _, Some(p)) => p.walk(it),
             PatKind::Struct(_, fields, _) => fields.iter().all(|field| field.pat.walk(it)),
-            PatKind::TupleStruct(_, s) | PatKind::Tuple(s) | PatKind::Slice(s) => {
-                s.iter().all(|p| p.walk(it))
-            }
+            PatKind::TupleStruct(_, s)
+            | PatKind::Tuple(s)
+            | PatKind::Slice(s)
+            | PatKind::Or(s) => s.iter().all(|p| p.walk(it)),
             PatKind::Box(s) | PatKind::Ref(s, _) | PatKind::Paren(s) => s.walk(it),
             PatKind::Wild
             | PatKind::Rest
@@ -648,6 +649,10 @@ pub enum PatKind {
     /// A tuple struct/variant pattern (`Variant(x, y, .., z)`).
     TupleStruct(Path, Vec<P<Pat>>),
 
+    /// An or-pattern `A | B | C`.
+    /// Invariant: `pats.len() >= 2`.
+    Or(Vec<P<Pat>>),
+
     /// A possibly qualified path pattern.
     /// Unqualified path patterns `A::B::C` can legally refer to variants, structs, constants
     /// or associated constants. Qualified path patterns `<A>::B::C`/`<A as Trait>::B::C` can

src/libsyntax/feature_gate.rs

@@ -559,6 +559,9 @@ declare_features! (
     // Allows `impl Trait` to be used inside type aliases (RFC 2515).
     (active, type_alias_impl_trait, "1.38.0", Some(63063), None),
 
+    // Allows the use of or-patterns, e.g. `0 | 1`.
+    (active, or_patterns, "1.38.0", Some(54883), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------
@@ -571,6 +574,7 @@ pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::impl_trait_in_bindings,
     sym::generic_associated_types,
     sym::const_generics,
+    sym::or_patterns,
     sym::let_chains,
 ];
 
@@ -2443,6 +2447,7 @@ pub fn check_crate(krate: &ast::Crate,
     gate_all!(let_chains_spans, let_chains, "`let` expressions in this position are experimental");
     gate_all!(async_closure_spans, async_closure, "async closures are unstable");
     gate_all!(yield_spans, generators, "yield syntax is experimental");
+    gate_all!(or_pattern_spans, or_patterns, "or-patterns syntax is experimental");
 
     let visitor = &mut PostExpansionVisitor {
         context: &ctx,

src/libsyntax/mut_visit.rs

@@ -1050,15 +1050,16 @@ pub fn noop_visit_pat<T: MutVisitor>(pat: &mut P<Pat>, vis: &mut T) {
                 vis.visit_span(span);
             };
         }
-        PatKind::Tuple(elems) => visit_vec(elems, |elem| vis.visit_pat(elem)),
         PatKind::Box(inner) => vis.visit_pat(inner),
         PatKind::Ref(inner, _mutbl) => vis.visit_pat(inner),
         PatKind::Range(e1, e2, Spanned { span: _, node: _ }) => {
             vis.visit_expr(e1);
             vis.visit_expr(e2);
             vis.visit_span(span);
         }
-        PatKind::Slice(elems) => visit_vec(elems, |elem| vis.visit_pat(elem)),
+        PatKind::Tuple(elems)
+        | PatKind::Slice(elems)
+        | PatKind::Or(elems) => visit_vec(elems, |elem| vis.visit_pat(elem)),
         PatKind::Paren(inner) => vis.visit_pat(inner),
         PatKind::Mac(mac) => vis.visit_mac(mac),
     }