3 files changed, 126 insertions, 89 deletions

diff --git a/crates/ra_syntax/src/ast/generated/nodes.rs b/crates/ra_syntax/src/ast/generated/nodes.rs
index 3fd761367..9d8127a3d 100644
--- a/crates/ra_syntax/src/ast/generated/nodes.rs
+++ b/crates/ra_syntax/src/ast/generated/nodes.rs
@@ -268,6 +268,36 @@ pub struct Rename {
 impl ast::NameOwner for Rename {}
 impl Rename {
     pub fn as_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![as]) }
+    pub fn underscore_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![_]) }
+}
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct UseTree {
+    pub(crate) syntax: SyntaxNode,
+}
+impl UseTree {
+    pub fn path(&self) -> Option<Path> { support::child(&self.syntax) }
+    pub fn coloncolon_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![::]) }
+    pub fn star_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![*]) }
+    pub fn use_tree_list(&self) -> Option<UseTreeList> { support::child(&self.syntax) }
+    pub fn rename(&self) -> Option<Rename> { support::child(&self.syntax) }
+}
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct Path {
+    pub(crate) syntax: SyntaxNode,
+}
+impl Path {
+    pub fn qualifier(&self) -> Option<Path> { support::child(&self.syntax) }
+    pub fn coloncolon_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![::]) }
+    pub fn segment(&self) -> Option<PathSegment> { support::child(&self.syntax) }
+}
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct UseTreeList {
+    pub(crate) syntax: SyntaxNode,
+}
+impl UseTreeList {
+    pub fn l_curly_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T!['{']) }
+    pub fn use_trees(&self) -> AstChildren<UseTree> { support::children(&self.syntax) }
+    pub fn r_curly_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T!['}']) }
 }
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct Abi {
@@ -433,15 +463,6 @@ impl PathType {
     pub fn path(&self) -> Option<Path> { support::child(&self.syntax) }
 }
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct Path {
-    pub(crate) syntax: SyntaxNode,
-}
-impl Path {
-    pub fn qualifier(&self) -> Option<Path> { support::child(&self.syntax) }
-    pub fn coloncolon_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![::]) }
-    pub fn segment(&self) -> Option<PathSegment> { support::child(&self.syntax) }
-}
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct PointerType {
     pub(crate) syntax: SyntaxNode,
 }
@@ -1178,26 +1199,6 @@ impl Param {
     pub fn dotdotdot_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![...]) }
 }
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct UseTree {
-    pub(crate) syntax: SyntaxNode,
-}
-impl UseTree {
-    pub fn path(&self) -> Option<Path> { support::child(&self.syntax) }
-    pub fn coloncolon_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![::]) }
-    pub fn star_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![*]) }
-    pub fn use_tree_list(&self) -> Option<UseTreeList> { support::child(&self.syntax) }
-    pub fn rename(&self) -> Option<Rename> { support::child(&self.syntax) }
-}
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct UseTreeList {
-    pub(crate) syntax: SyntaxNode,
-}
-impl UseTreeList {
-    pub fn l_curly_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T!['{']) }
-    pub fn use_trees(&self) -> AstChildren<UseTree> { support::children(&self.syntax) }
-    pub fn r_curly_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T!['}']) }
-}
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct PathSegment {
     pub(crate) syntax: SyntaxNode,
 }
@@ -1627,6 +1628,39 @@ impl AstNode for Rename {
     }
     fn syntax(&self) -> &SyntaxNode { &self.syntax }
 }
+impl AstNode for UseTree {
+    fn can_cast(kind: SyntaxKind) -> bool { kind == USE_TREE }
+    fn cast(syntax: SyntaxNode) -> Option<Self> {
+        if Self::can_cast(syntax.kind()) {
+            Some(Self { syntax })
+        } else {
+            None
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode { &self.syntax }
+}
+impl AstNode for Path {
+    fn can_cast(kind: SyntaxKind) -> bool { kind == PATH }
+    fn cast(syntax: SyntaxNode) -> Option<Self> {
+        if Self::can_cast(syntax.kind()) {
+            Some(Self { syntax })
+        } else {
+            None
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode { &self.syntax }
+}
+impl AstNode for UseTreeList {
+    fn can_cast(kind: SyntaxKind) -> bool { kind == USE_TREE_LIST }
+    fn cast(syntax: SyntaxNode) -> Option<Self> {
+        if Self::can_cast(syntax.kind()) {
+            Some(Self { syntax })
+        } else {
+            None
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode { &self.syntax }
+}
 impl AstNode for Abi {
     fn can_cast(kind: SyntaxKind) -> bool { kind == ABI }
     fn cast(syntax: SyntaxNode) -> Option<Self> {
@@ -1825,17 +1859,6 @@ impl AstNode for PathType {
     }
     fn syntax(&self) -> &SyntaxNode { &self.syntax }
 }
-impl AstNode for Path {
-    fn can_cast(kind: SyntaxKind) -> bool { kind == PATH }
-    fn cast(syntax: SyntaxNode) -> Option<Self> {
-        if Self::can_cast(syntax.kind()) {
-            Some(Self { syntax })
-        } else {
-            None
-        }
-    }
-    fn syntax(&self) -> &SyntaxNode { &self.syntax }
-}
 impl AstNode for PointerType {
     fn can_cast(kind: SyntaxKind) -> bool { kind == POINTER_TYPE }
     fn cast(syntax: SyntaxNode) -> Option<Self> {
@@ -2672,28 +2695,6 @@ impl AstNode for Param {
     }
     fn syntax(&self) -> &SyntaxNode { &self.syntax }
 }
-impl AstNode for UseTree {
-    fn can_cast(kind: SyntaxKind) -> bool { kind == USE_TREE }
-    fn cast(syntax: SyntaxNode) -> Option<Self> {
-        if Self::can_cast(syntax.kind()) {
-            Some(Self { syntax })
-        } else {
-            None
-        }
-    }
-    fn syntax(&self) -> &SyntaxNode { &self.syntax }
-}
-impl AstNode for UseTreeList {
-    fn can_cast(kind: SyntaxKind) -> bool { kind == USE_TREE_LIST }
-    fn cast(syntax: SyntaxNode) -> Option<Self> {
-        if Self::can_cast(syntax.kind()) {
-            Some(Self { syntax })
-        } else {
-            None
-        }
-    }
-    fn syntax(&self) -> &SyntaxNode { &self.syntax }
-}
 impl AstNode for PathSegment {
     fn can_cast(kind: SyntaxKind) -> bool { kind == PATH_SEGMENT }
     fn cast(syntax: SyntaxNode) -> Option<Self> {
@@ -3560,6 +3561,21 @@ impl std::fmt::Display for Rename {
         std::fmt::Display::fmt(self.syntax(), f)
     }
 }
+impl std::fmt::Display for UseTree {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        std::fmt::Display::fmt(self.syntax(), f)
+    }
+}
+impl std::fmt::Display for Path {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        std::fmt::Display::fmt(self.syntax(), f)
+    }
+}
+impl std::fmt::Display for UseTreeList {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        std::fmt::Display::fmt(self.syntax(), f)
+    }
+}
 impl std::fmt::Display for Abi {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         std::fmt::Display::fmt(self.syntax(), f)
@@ -3650,11 +3666,6 @@ impl std::fmt::Display for PathType {
         std::fmt::Display::fmt(self.syntax(), f)
     }
 }
-impl std::fmt::Display for Path {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        std::fmt::Display::fmt(self.syntax(), f)
-    }
-}
 impl std::fmt::Display for PointerType {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         std::fmt::Display::fmt(self.syntax(), f)
@@ -4035,16 +4046,6 @@ impl std::fmt::Display for Param {
         std::fmt::Display::fmt(self.syntax(), f)
     }
 }
-impl std::fmt::Display for UseTree {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        std::fmt::Display::fmt(self.syntax(), f)
-    }
-}
-impl std::fmt::Display for UseTreeList {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        std::fmt::Display::fmt(self.syntax(), f)
-    }
-}
 impl std::fmt::Display for PathSegment {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         std::fmt::Display::fmt(self.syntax(), f)
diff --git a/xtask/src/codegen/gen_syntax.rs b/xtask/src/codegen/gen_syntax.rs
index 9b49712c1..c77fc8a8d 100644
--- a/xtask/src/codegen/gen_syntax.rs
+++ b/xtask/src/codegen/gen_syntax.rs
@@ -543,6 +543,10 @@ fn lower_enum(grammar: &Grammar, rule: &Rule) -> Option<Vec<String>> {
 }
 
 fn lower_rule(acc: &mut Vec<Field>, grammar: &Grammar, rule: &Rule) {
+    if lower_comma_list(acc, grammar, rule) {
+        return;
+    }
+
     match rule {
         Rule::Node(node) => {
             let field = Field::Node { name: grammar[*node].name.clone(), src: FieldSrc::Shorthand };
@@ -595,6 +599,37 @@ fn lower_rule(acc: &mut Vec<Field>, grammar: &Grammar, rule: &Rule) {
     }
 }
 
+// (T (',' T)* ','?)?
+fn lower_comma_list(acc: &mut Vec<Field>, grammar: &Grammar, rule: &Rule) -> bool {
+    let rule = match rule {
+        Rule::Opt(it) => it,
+        _ => return false,
+    };
+    let rule = match &**rule {
+        Rule::Seq(it) => it,
+        _ => return false,
+    };
+    let (node, repeat, trailing_comma) = match rule.as_slice() {
+        [Rule::Node(node), Rule::Rep(repeat), Rule::Opt(trailing_comma)] => {
+            (node, repeat, trailing_comma)
+        }
+        _ => return false,
+    };
+    let repeat = match &**repeat {
+        Rule::Seq(it) => it,
+        _ => return false,
+    };
+    match repeat.as_slice() {
+        [comma, Rule::Node(n)] if comma == &**trailing_comma && n == node => (),
+        _ => return false,
+    }
+    let name = grammar[*node].name.clone();
+    let label = pluralize(&to_lower_snake_case(&name));
+    let field = Field::Node { name: label.clone(), src: FieldSrc::Many(name) };
+    acc.push(field);
+    true
+}
+
 fn deduplicate_fields(ast: &mut AstSrc) {
     for node in &mut ast.nodes {
         let mut i = 0;
diff --git a/xtask/src/codegen/rust.ungram b/xtask/src/codegen/rust.ungram
index e6e7c7518..2ba68457f 100644
--- a/xtask/src/codegen/rust.ungram
+++ b/xtask/src/codegen/rust.ungram
@@ -29,6 +29,19 @@ ItemList =
 ExternCrate =
   Attr* Visibility? 'extern' 'crate' (NameRef | 'self') Rename? ';'
 
+Rename =
+  'as' (Name | '_')
+
+UseItem =
+  Attr* Visibility? 'use' UseTree ';'
+
+UseTree =
+  (Path? '::')? ('*' | UseTreeList )
+| Path Rename?
+
+UseTreeList =
+  '{' (UseTree (',' UseTree)* ','?)? '}'
+
 FnDef =
  Attr* Visibility? Abi? 'const' 'default' 'async' 'unsafe' 'fn' Name TypeParamList?
  ParamList RetType?
@@ -395,18 +408,6 @@ Param =
   Attr* Pat (':' ascribed_type:TypeRef)
 | '...'
 
-UseItem =
-  Attr* Visibility? 'use' UseTree ';'
-
-UseTree =
-  Path ('::' ('*' | UseTreeList))  Rename?
-
-UseTreeList =
-  '{' UseTree* '}'
-
-Rename =
-  'as' Name
-
 Path =
   (qualifier:Path '::')? segment:PathSegment