Merge #1848

1848: Parse `..` as a full pattern r=matklad a=ecstatic-morse

Resolves #1479.

This PR implements [RFC 2707](rust-lang/rfcs#2707) in the parser. It introduces a new `DotDotPat` AST node modeled on `PlaceholderPat` and changes the parsing of tuple and slice patterns to conform to the RFC.

Notably, this PR does *not* change the resulting AST when `..` appears in a struct pattern (e.g. `Struct { a, b: c, .. }`). I *think* this is the behavior mandated by RFC 2707, but someone should confirm this.

Co-authored-by: Dylan MacKenzie <ecstaticmorse@gmail.com>

Author: bors[bot]

crates/ra_hir/src/expr/lower.rs

@@ -573,6 +573,7 @@ where
             }
 
             // FIXME: implement
+            ast::Pat::DotDotPat(_) => Pat::Missing,
             ast::Pat::BoxPat(_) => Pat::Missing,
             ast::Pat::LiteralPat(_) => Pat::Missing,
             ast::Pat::SlicePat(_) | ast::Pat::RangePat(_) => Pat::Missing,

crates/ra_parser/src/grammar/patterns.rs

@@ -2,7 +2,7 @@ use super::*;
 
 pub(super) const PATTERN_FIRST: TokenSet = expressions::LITERAL_FIRST
     .union(paths::PATH_FIRST)
-    .union(token_set![BOX_KW, REF_KW, MUT_KW, L_PAREN, L_BRACK, AMP, UNDERSCORE, MINUS]);
+    .union(token_set![BOX_KW, REF_KW, MUT_KW, L_PAREN, L_BRACK, AMP, UNDERSCORE, MINUS, DOT]);
 
 pub(crate) fn pattern(p: &mut Parser) {
     pattern_r(p, PAT_RECOVERY_SET);
@@ -73,6 +73,7 @@ fn atom_pat(p: &mut Parser, recovery_set: TokenSet) -> Option<CompletedMarker> {
         _ if paths::is_use_path_start(p) => path_pat(p),
         _ if is_literal_pat_start(p) => literal_pat(p),
 
+        T![.] if p.at(T![..]) => dot_dot_pat(p),
         T![_] => placeholder_pat(p),
         T![&] => ref_pat(p),
         T!['('] => tuple_pat(p),
@@ -163,7 +164,9 @@ fn record_field_pat_list(p: &mut Parser) {
     p.bump_any();
     while !p.at(EOF) && !p.at(T!['}']) {
         match p.current() {
+            // A trailing `..` is *not* treated as a DOT_DOT_PAT.
             T![.] if p.at(T![..]) => p.bump(T![..]),
+
             IDENT if p.nth(1) == T![:] => record_field_pat(p),
             T!['{'] => error_block(p, "expected ident"),
             T![box] => {
@@ -201,6 +204,39 @@ fn placeholder_pat(p: &mut Parser) -> CompletedMarker {
     m.complete(p, PLACEHOLDER_PAT)
 }
 
+// test dot_dot_pat
+// fn main() {
+//     let .. = ();
+//     //
+//     // Tuples
+//     //
+//     let (a, ..) = ();
+//     let (a, ..,) = ();
+//     let Tuple(a, ..) = ();
+//     let Tuple(a, ..,) = ();
+//     let (.., ..) = ();
+//     let Tuple(.., ..) = ();
+//     let (.., a, ..) = ();
+//     let Tuple(.., a, ..) = ();
+//     //
+//     // Slices
+//     //
+//     let [..] = ();
+//     let [head, ..] = ();
+//     let [head, tail @ ..] = ();
+//     let [head, .., cons] = ();
+//     let [head, mid @ .., cons] = ();
+//     let [head, .., .., cons] = ();
+//     let [head, .., mid, tail @ ..] = ();
+//     let [head, .., mid, .., cons] = ();
+// }
+fn dot_dot_pat(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(T![..]));
+    let m = p.start();
+    p.bump(T![..]);
+    m.complete(p, DOT_DOT_PAT)
+}
+
 // test ref_pat
 // fn main() {
 //     let &a = ();
@@ -241,16 +277,12 @@ fn slice_pat(p: &mut Parser) -> CompletedMarker {
 
 fn pat_list(p: &mut Parser, ket: SyntaxKind) {
     while !p.at(EOF) && !p.at(ket) {
-        match p.current() {
-            T![.] if p.at(T![..]) => p.bump(T![..]),
-            _ => {
-                if !p.at_ts(PATTERN_FIRST) {
-                    p.error("expected a pattern");
-                    break;
-                }
-                pattern(p)
-            }
+        if !p.at_ts(PATTERN_FIRST) {
+            p.error("expected a pattern");
+            break;
         }
+
+        pattern(p);
         if !p.at(ket) {
             p.expect(T![,]);
         }

crates/ra_parser/src/syntax_kind/generated.rs

@@ -152,6 +152,7 @@ pub enum SyntaxKind {
     BOX_PAT,
     BIND_PAT,
     PLACEHOLDER_PAT,
+    DOT_DOT_PAT,
     PATH_PAT,
     RECORD_PAT,
     RECORD_FIELD_PAT_LIST,

crates/ra_syntax/src/ast/generated.rs

@@ -532,6 +532,29 @@ impl AstNode for ContinueExpr {
 }
 impl ContinueExpr {}
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct DotDotPat {
+    pub(crate) syntax: SyntaxNode,
+}
+impl AstNode for DotDotPat {
+    fn can_cast(kind: SyntaxKind) -> bool {
+        match kind {
+            DOT_DOT_PAT => true,
+            _ => false,
+        }
+    }
+    fn cast(syntax: SyntaxNode) -> Option<Self> {
+        if Self::can_cast(syntax.kind()) {
+            Some(Self { syntax })
+        } else {
+            None
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode {
+        &self.syntax
+    }
+}
+impl DotDotPat {}
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct DynTraitType {
     pub(crate) syntax: SyntaxNode,
 }
@@ -2128,6 +2151,7 @@ pub enum Pat {
     BoxPat(BoxPat),
     BindPat(BindPat),
     PlaceholderPat(PlaceholderPat),
+    DotDotPat(DotDotPat),
     PathPat(PathPat),
     RecordPat(RecordPat),
     TupleStructPat(TupleStructPat),
@@ -2156,6 +2180,11 @@ impl From<PlaceholderPat> for Pat {
         Pat::PlaceholderPat(node)
     }
 }
+impl From<DotDotPat> for Pat {
+    fn from(node: DotDotPat) -> Pat {
+        Pat::DotDotPat(node)
+    }
+}
 impl From<PathPat> for Pat {
     fn from(node: PathPat) -> Pat {
         Pat::PathPat(node)
@@ -2194,8 +2223,10 @@ impl From<LiteralPat> for Pat {
 impl AstNode for Pat {
     fn can_cast(kind: SyntaxKind) -> bool {
         match kind {
-            REF_PAT | BOX_PAT | BIND_PAT | PLACEHOLDER_PAT | PATH_PAT | RECORD_PAT
-            | TUPLE_STRUCT_PAT | TUPLE_PAT | SLICE_PAT | RANGE_PAT | LITERAL_PAT => true,
+            REF_PAT | BOX_PAT | BIND_PAT | PLACEHOLDER_PAT | DOT_DOT_PAT | PATH_PAT
+            | RECORD_PAT | TUPLE_STRUCT_PAT | TUPLE_PAT | SLICE_PAT | RANGE_PAT | LITERAL_PAT => {
+                true
+            }
             _ => false,
         }
     }
@@ -2205,6 +2236,7 @@ impl AstNode for Pat {
             BOX_PAT => Pat::BoxPat(BoxPat { syntax }),
             BIND_PAT => Pat::BindPat(BindPat { syntax }),
             PLACEHOLDER_PAT => Pat::PlaceholderPat(PlaceholderPat { syntax }),
+            DOT_DOT_PAT => Pat::DotDotPat(DotDotPat { syntax }),
             PATH_PAT => Pat::PathPat(PathPat { syntax }),
             RECORD_PAT => Pat::RecordPat(RecordPat { syntax }),
             TUPLE_STRUCT_PAT => Pat::TupleStructPat(TupleStructPat { syntax }),
@@ -2222,6 +2254,7 @@ impl AstNode for Pat {
             Pat::BoxPat(it) => &it.syntax,
             Pat::BindPat(it) => &it.syntax,
             Pat::PlaceholderPat(it) => &it.syntax,
+            Pat::DotDotPat(it) => &it.syntax,
             Pat::PathPat(it) => &it.syntax,
             Pat::RecordPat(it) => &it.syntax,
             Pat::TupleStructPat(it) => &it.syntax,

crates/ra_syntax/src/grammar.ron

@@ -161,6 +161,7 @@ Grammar(
         "BOX_PAT",
         "BIND_PAT",
         "PLACEHOLDER_PAT",
+        "DOT_DOT_PAT",
         "PATH_PAT",
         "RECORD_PAT",
         "RECORD_FIELD_PAT_LIST",
@@ -532,6 +533,7 @@ Grammar(
             traits: ["NameOwner"]
         ),
         "PlaceholderPat": (),
+        "DotDotPat": (),
         "PathPat": ( options: [ "Path" ] ),
         "RecordPat": ( options: ["RecordFieldPatList", "Path"] ),
         "RecordFieldPatList": (
@@ -559,6 +561,7 @@ Grammar(
                 "BoxPat",
                 "BindPat",
                 "PlaceholderPat",
+                "DotDotPat",
                 "PathPat",
                 "RecordPat",
                 "TupleStructPat",

crates/ra_syntax/test_data/parser/inline/ok/0008_path_part.txt

@@ -82,7 +82,8 @@ SOURCE_FILE@[0; 103)
                 NAME_REF@[87; 90)
                   IDENT@[87; 90) "Bar"
             L_PAREN@[90; 91) "("
-            DOTDOT@[91; 93) ".."
+            DOT_DOT_PAT@[91; 93)
+              DOTDOT@[91; 93) ".."
             R_PAREN@[93; 94) ")"
           WHITESPACE@[94; 95) " "
           EQ@[95; 96) "="

crates/ra_syntax/test_data/parser/inline/ok/0024_slice_pat.txt

@@ -27,7 +27,8 @@ SOURCE_FILE@[0; 39)
                 IDENT@[24; 25) "b"
             COMMA@[25; 26) ","
             WHITESPACE@[26; 27) " "
-            DOTDOT@[27; 29) ".."
+            DOT_DOT_PAT@[27; 29)
+              DOTDOT@[27; 29) ".."
             R_BRACK@[29; 30) "]"
           WHITESPACE@[30; 31) " "
           EQ@[31; 32) "="

crates/ra_syntax/test_data/parser/inline/ok/0026_tuple_pat_fields.txt

@@ -84,7 +84,8 @@ SOURCE_FILE@[0; 97)
               UNDERSCORE@[78; 79) "_"
             COMMA@[79; 80) ","
             WHITESPACE@[80; 81) " "
-            DOTDOT@[81; 83) ".."
+            DOT_DOT_PAT@[81; 83)
+              DOTDOT@[81; 83) ".."
             WHITESPACE@[83; 84) " "
             COMMA@[84; 85) ","
             WHITESPACE@[85; 86) " "

crates/ra_syntax/test_data/parser/inline/ok/0111_tuple_pat.txt

@@ -27,7 +27,8 @@ SOURCE_FILE@[0; 39)
                 IDENT@[24; 25) "b"
             COMMA@[25; 26) ","
             WHITESPACE@[26; 27) " "
-            DOTDOT@[27; 29) ".."
+            DOT_DOT_PAT@[27; 29)
+              DOTDOT@[27; 29) ".."
             R_PAREN@[29; 30) ")"
           WHITESPACE@[30; 31) " "
           EQ@[31; 32) "="

crates/ra_syntax/test_data/parser/inline/ok/0144_dot_dot_pat.rs

@@ -0,0 +1,25 @@
+fn main() {
+    let .. = ();
+    //
+    // Tuples
+    //
+    let (a, ..) = ();
+    let (a, ..,) = ();
+    let Tuple(a, ..) = ();
+    let Tuple(a, ..,) = ();
+    let (.., ..) = ();
+    let Tuple(.., ..) = ();
+    let (.., a, ..) = ();
+    let Tuple(.., a, ..) = ();
+    //
+    // Slices
+    //
+    let [..] = ();
+    let [head, ..] = ();
+    let [head, tail @ ..] = ();
+    let [head, .., cons] = ();
+    let [head, mid @ .., cons] = ();
+    let [head, .., .., cons] = ();
+    let [head, .., mid, tail @ ..] = ();
+    let [head, .., mid, .., cons] = ();
+}