don't parse subslice pats outside of slice pats

Author: tomjakubowski

crates/ra_parser/src/grammar/patterns.rs

@@ -5,7 +5,12 @@ pub(super) const PATTERN_FIRST: TokenSet = expressions::LITERAL_FIRST
     .union(token_set![REF_KW, MUT_KW, L_PAREN, L_BRACK, AMP, UNDERSCORE, MINUS]);
 
 pub(super) fn pattern(p: &mut Parser) {
-    pattern_r(p, PAT_RECOVERY_SET);
+    pattern_r(p, PAT_RECOVERY_SET, false);
+}
+
+fn pattern_with_subslice_patterns(p: &mut Parser) {
+    // Subslice patterns are only allowed within a slice pattern
+    pattern_r(p, PAT_RECOVERY_SET, true);
 }
 
 /// Parses a pattern list separated by pipes `|`
@@ -17,14 +22,14 @@ pub(super) fn pattern_list(p: &mut Parser) {
 /// using the given `recovery_set`
 pub(super) fn pattern_list_r(p: &mut Parser, recovery_set: TokenSet) {
     p.eat(T![|]);
-    pattern_r(p, recovery_set);
+    pattern_r(p, recovery_set, false);
 
     while p.eat(T![|]) {
-        pattern_r(p, recovery_set);
+        pattern_r(p, recovery_set, false);
     }
 }
 
-pub(super) fn pattern_r(p: &mut Parser, recovery_set: TokenSet) {
+pub(super) fn pattern_r(p: &mut Parser, recovery_set: TokenSet, subslice_patterns: bool) {
     if let Some(lhs) = atom_pat(p, recovery_set) {
         // test range_pat
         // fn main() {
@@ -38,7 +43,7 @@ pub(super) fn pattern_r(p: &mut Parser, recovery_set: TokenSet) {
             let m = lhs.precede(p);
             let dots = p.current();
             p.bump();
-            if dots == T![..] && !p.at_ts(PATTERN_FIRST) {
+            if subslice_patterns && dots == T![..] && !p.at_ts(PATTERN_FIRST) {
                 m.complete(p, SUBSLICE_PAT);
             } else {
                 atom_pat(p, recovery_set);
@@ -158,7 +163,7 @@ fn tuple_pat_fields(p: &mut Parser) {
                     p.error("expected a pattern");
                     break;
                 }
-                pattern(p)
+                pattern_with_subslice_patterns(p);
             }
         }
         if !p.at(T![')']) {
@@ -262,8 +267,7 @@ fn slice_pat(p: &mut Parser) -> CompletedMarker {
                     p.error("expected a pattern");
                     break;
                 }
-                pattern(p);
-                p.eat(T![..]);
+                pattern_with_subslice_patterns(p);
             }
         }
         if !p.at(T![']']) {