allow aliases in underscores

this helps with

    use foo::Trait as _;

syntax

4 files changed, 21 insertions, 2 deletions

diff --git a/crates/ra_parser/src/grammar.rs b/crates/ra_parser/src/grammar.rs
index f94702e97..c9941fe93 100644
--- a/crates/ra_parser/src/grammar.rs
+++ b/crates/ra_parser/src/grammar.rs
@@ -129,7 +129,9 @@ fn opt_alias(p: &mut Parser) {
     if p.at(AS_KW) {
         let m = p.start();
         p.bump();
-        name(p);
+        if !p.eat(UNDERSCORE) {
+            name(p);
+        }
         m.complete(p, ALIAS);
     }
 }
diff --git a/crates/ra_parser/src/grammar/items/use_item.rs b/crates/ra_parser/src/grammar/items/use_item.rs
index 5111d37eb..b36612726 100644
--- a/crates/ra_parser/src/grammar/items/use_item.rs
+++ b/crates/ra_parser/src/grammar/items/use_item.rs
@@ -76,6 +76,7 @@ fn use_tree(p: &mut Parser) {
                     //  yet::another::path,
                     //  running::out::of::synonyms::for_::different::*
                     // };
+                    // use Trait as _;
                     opt_alias(p);
                 }
                 COLONCOLON => {
diff --git a/crates/ra_syntax/tests/data/parser/inline/ok/0043_use_alias.rs b/crates/ra_syntax/tests/data/parser/inline/ok/0043_use_alias.rs
index 544caa020..9be50f877 100644
--- a/crates/ra_syntax/tests/data/parser/inline/ok/0043_use_alias.rs
+++ b/crates/ra_syntax/tests/data/parser/inline/ok/0043_use_alias.rs
@@ -5,3 +5,4 @@ use some::{
  yet::another::path,
  running::out::of::synonyms::for_::different::*
 };
+use Trait as _;
diff --git a/crates/ra_syntax/tests/data/parser/inline/ok/0043_use_alias.txt b/crates/ra_syntax/tests/data/parser/inline/ok/0043_use_alias.txt
index 8ef0ecbc6..0c8dec81d 100644
--- a/crates/ra_syntax/tests/data/parser/inline/ok/0043_use_alias.txt
+++ b/crates/ra_syntax/tests/data/parser/inline/ok/0043_use_alias.txt
@@ -1,4 +1,4 @@
-SOURCE_FILE@[0; 182)
+SOURCE_FILE@[0; 198)
   USE_ITEM@[0; 28)
     USE_KW@[0; 3)
     WHITESPACE@[3; 4)
@@ -121,3 +121,18 @@ SOURCE_FILE@[0; 182)
         R_CURLY@[179; 180)
     SEMI@[180; 181)
   WHITESPACE@[181; 182)
+  USE_ITEM@[182; 197)
+    USE_KW@[182; 185)
+    WHITESPACE@[185; 186)
+    USE_TREE@[186; 196)
+      PATH@[186; 191)
+        PATH_SEGMENT@[186; 191)
+          NAME_REF@[186; 191)
+            IDENT@[186; 191) "Trait"
+      WHITESPACE@[191; 192)
+      ALIAS@[192; 196)
+        AS_KW@[192; 194)
+        WHITESPACE@[194; 195)
+        UNDERSCORE@[195; 196)
+    SEMI@[196; 197)
+  WHITESPACE@[197; 198)