2 files changed, 189 insertions, 158 deletions

diff --git a/xtask/src/codegen/gen_syntax.rs b/xtask/src/codegen/gen_syntax.rs
index d9f358513..059538696 100644
--- a/xtask/src/codegen/gen_syntax.rs
+++ b/xtask/src/codegen/gen_syntax.rs
@@ -579,6 +579,21 @@ fn lower_rule(acc: &mut Vec<Field>, grammar: &Grammar, label: Option<&String>, r
         }
         Rule::Labeled { label: l, rule } => {
             assert!(label.is_none());
+            let manually_implemented = matches!(
+                l.as_str(),
+                "lhs"
+                    | "rhs"
+                    | "then_branch"
+                    | "else_branch"
+                    | "start"
+                    | "end"
+                    | "op"
+                    | "index"
+                    | "base"
+            );
+            if manually_implemented {
+                return;
+            }
             lower_rule(acc, grammar, Some(l), rule);
         }
         Rule::Seq(rules) | Rule::Alt(rules) => {
diff --git a/xtask/src/codegen/rust.ungram b/xtask/src/codegen/rust.ungram
index 17de36d7a..aef07cb1e 100644
--- a/xtask/src/codegen/rust.ungram
+++ b/xtask/src/codegen/rust.ungram
@@ -115,8 +115,8 @@ Union =
   RecordFieldList
 
 AdtDef =
-  Struct
-| Enum
+  Enum
+| Struct
 | Union
 
 Const =
@@ -136,10 +136,10 @@ AssocItemList =
   '{' Attr* AssocItem* '}'
 
 AssocItem =
-  Fn
-| TypeAlias
-| Const
+  Const
+| Fn
 | MacroCall
+| TypeAlias
 
 Impl =
  Attr* Visibility?
@@ -162,9 +162,9 @@ GenericParamList =
   '<' (GenericParam (',' GenericParam)* ','?)? '>'
 
 GenericParam =
-  LifetimeParam
+  ConstParam
+| LifetimeParam
 | TypeParam
-| ConstParam
 
 TypeParam =
   Attr* Name (':' TypeBoundList?)?
@@ -195,9 +195,9 @@ Attr =
   '#' '!'? '[' Path ('=' Literal | TokenTree)? ']'
 
 Stmt =
-  LetStmt
-| ExprStmt
+  ExprStmt
 | Item
+| LetStmt
 
 LetStmt =
   Attr* 'let' Pat (':' Type)?
@@ -206,189 +206,238 @@ LetStmt =
 ExprStmt =
   Attr* Expr ';'?
 
-Type =
-  ParenType
-| TupleType
-| NeverType
-| PathType
-| PointerType
-| ArrayType
-| SliceType
-| ReferenceType
-| InferType
-| FnPointerType
-| ForType
-| ImplTraitType
-| DynTraitType
+Expr =
+  ArrayExpr
+| AwaitExpr
+| BinExpr
+| BlockExpr
+| BoxExpr
+| BreakExpr
+| CallExpr
+| CastExpr
+| ContinueExpr
+| EffectExpr
+| FieldExpr
+| ForExpr
+| IfExpr
+| IndexExpr
+| Label
+| ClosureExpr
+| Literal
+| LoopExpr
+| MacroCall
+| MatchExpr
+| MethodCallExpr
+| ParenExpr
+| PathExpr
+| PrefixExpr
+| RangeExpr
+| RecordExpr
+| RefExpr
+| ReturnExpr
+| TryExpr
+| TupleExpr
+| WhileExpr
 
-ParenType =
-  '(' Type ')'
+Literal =
+  Attr* 'int_number'
 
-NeverType =
-  '!'
+PathExpr =
+  Attr* Path
 
-PathType =
-  Path
+BlockExpr =
+  '{'
+    Attr*
+    statements:Stmt*
+    Expr?
+  '}'
 
-TupleType =
-  '(' fields:(Type (',' Type)* ','?)? ')'
+RefExpr =
+  Attr* '&' ('raw' |'mut' | 'const') Expr
 
-PointerType =
-  '*' ('const' | 'mut') Type
+TryExpr =
+  Attr* Expr '?'
 
-ReferenceType =
-  '&' 'lifetime'? 'mut'? Type
+EffectExpr =
+  Attr* Label? ('try' | 'unsafe' | 'async') BlockExpr
 
-ArrayType =
-  '[' Type ';' Expr ']'
+PrefixExpr =
+  Attr* op:('-' | '!' | '*') Expr
 
-SliceType =
-  '[' Type ']'
+BinExpr =
+  Attr*
+  lhs:Expr
+  op:(
+    '||' | '&&'
+    | '==' | '!=' | '<=' | '>=' | '<' | '>'
+    | '+' | '*' | '-' | '/' | '%' | '<<' | '>>' | '^' | '|' | '&'
+    | '=' | '+=' | '/=' | '*=' | '%=' | '>>=' | '<<=' | '-=' | '|=' | '&=' | '^='
+  )
+  rhs:Expr
 
-InferType =
-   '_'
+CastExpr =
+  Attr* Expr 'as' Type
 
-FnPointerType =
-   'const'? 'async'? 'unsafe'? Abi? 'fn' ParamList RetType?
+ParenExpr =
+  Attr* '(' Attr* Expr ')'
 
-ForType =
-   'for' GenericParamList Type
+ArrayExpr =
+  Attr* '[' Attr* (
+    (Expr (',' Expr)* ','?)?
+  | Expr ';' Expr
+  ) ']'
 
-ImplTraitType =
-  'impl' TypeBoundList
+IndexExpr =
+  Attr* base:Expr '[' index:Expr ']'
 
-DynTraitType =
-  'dyn' TypeBoundList
+TupleExpr =
+  Attr* '(' Attr* (Expr (',' Expr)* ','?)? ')'
 
-TypeBoundList =
-   bounds:(TypeBound ('+' TypeBound)* '+'?)
+RecordExpr =
+  Path RecordExprFieldList
 
-TypeBound =
-  'lifetime'
-| '?'? Type
+RecordExprFieldList =
+  '{'
+    Attr*
+    fields:(RecordExprField (',' RecordExprField)* ','?)
+    ('..' spread:Expr)?
+  '}'
 
-TupleExpr =
-  Attr* '(' Expr* ')'
+RecordExprField =
+  Attr* NameRef (':' Expr)?
 
-ArrayExpr =
-  Attr* '[' (Expr* | Expr ';' Expr) ']'
+CallExpr =
+  Attr* Expr ArgList
 
-ParenExpr =
-  Attr* '(' Expr ')'
+ArgList =
+  '(' args:(Expr (',' Expr)* ','?)? ')'
 
-PathExpr =
-  Path
+MethodCallExpr =
+  Attr* Expr '.' NameRef TypeArgList? ArgList
+
+FieldExpr =
+  Attr* Expr '.' NameRef
 
-LambdaExpr =
+ClosureExpr =
   Attr* 'static'? 'async'? 'move'?  ParamList RetType?
   body:Expr
 
 IfExpr =
-  Attr* 'if' Condition
+  Attr* 'if' Condition then_branch:BlockExpr
+  ('else' else_branch:(IfExpr | BlockExpr))?
 
 Condition =
   'let' Pat '=' Expr
 | Expr
 
-EffectExpr =
-  Attr* Label? ('try' | 'unsafe' | 'async') BlockExpr
-
 LoopExpr =
   Attr* Label? 'loop'
-  loop_body:BlockExpr?
+  loop_body:BlockExpr
 
 ForExpr =
   Attr* Label? 'for' Pat 'in' iterable:Expr
-  loop_body:BlockExpr?
+  loop_body:BlockExpr
 
 WhileExpr =
   Attr* Label? 'while' Condition
   loop_body:BlockExpr?
 
-ContinueExpr =
-  Attr* 'continue' 'lifetime'?
+Label =
+  'lifetime'
 
 BreakExpr =
   Attr* 'break' 'lifetime'? Expr?
 
-Label =
-  'lifetime'
-
-BlockExpr =
-  Attr* Label
-  '{'
-    statements:Stmt*
-    Expr?
-  '}'
+ContinueExpr =
+  Attr* 'continue' 'lifetime'?
 
-ReturnExpr =
-  Attr* 'return' Expr
+RangeExpr =
+  Attr* start:Expr? op:('..' | '..=') end:Expr?
 
-CallExpr =
-  Attr* Expr ArgList
+MatchExpr =
+  Attr* 'match' Expr MatchArmList
 
-MethodCallExpr =
-  Attr* Expr '.' NameRef TypeArgList? ArgList
+MatchArmList =
+  '{'
+    Attr*
+    arms:MatchArm*
+  '}'
 
-ArgList =
-  '(' args:Expr* ')'
+MatchArm =
+  Attr* Pat guard:MatchGuard? '=>' Expr ','?
 
-FieldExpr =
-  Attr* Expr '.' NameRef
+MatchGuard =
+  'if' Expr
 
-IndexExpr =
-  Attr* '[' ']'
+ReturnExpr =
+  Attr* 'return' Expr?
 
 AwaitExpr =
   Attr* Expr '.' 'await'
 
-TryExpr =
-  Attr* Expr '?'
+BoxExpr =
+  Attr* 'box' Expr
 
-CastExpr =
-  Attr* Expr 'as' Type
+Type =
+  ArrayType
+| DynTraitType
+| FnPointerType
+| ForType
+| ImplTraitType
+| InferType
+| NeverType
+| ParenType
+| PathType
+| PointerType
+| ReferenceType
+| SliceType
+| TupleType
 
-RefExpr =
-  Attr* '&' ('raw' | 'mut' | 'const') Expr
+ParenType =
+  '(' Type ')'
 
-PrefixExpr =
-  Attr* Expr
+NeverType =
+  '!'
 
-BoxExpr =
-  Attr* 'box' Expr
+PathType =
+  Path
 
-RangeExpr =
-  Attr*
+TupleType =
+  '(' fields:(Type (',' Type)* ','?)? ')'
 
-BinExpr =
-  Attr*
+PointerType =
+  '*' ('const' | 'mut') Type
 
-Literal =
-  'int_number'
+ReferenceType =
+  '&' 'lifetime'? 'mut'? Type
 
-MatchExpr =
-  Attr* 'match' Expr MatchArmList
+ArrayType =
+  '[' Type ';' Expr ']'
 
-MatchArmList =
-  '{' arms:MatchArm* '}'
+SliceType =
+  '[' Type ']'
 
-MatchArm =
-  Attr* Pat guard:MatchGuard? '=>' Expr
+InferType =
+   '_'
 
-MatchGuard =
-  'if' Expr
+FnPointerType =
+   'const'? 'async'? 'unsafe'? Abi? 'fn' ParamList RetType?
 
-RecordExpr =
- Path RecordExprFieldList
+ForType =
+   'for' GenericParamList Type
 
-RecordExprFieldList =
-  '{'
-    fields:RecordExprField*
-    ('..' spread:Expr)?
-  '}'
+ImplTraitType =
+  'impl' TypeBoundList
 
-RecordExprField =
-  Attr* NameRef (':' Expr)?
+DynTraitType =
+  'dyn' TypeBoundList
+
+TypeBoundList =
+   bounds:(TypeBound ('+' TypeBound)* '+'?)
+
+TypeBound =
+  'lifetime'
+| '?'? Type
 
 OrPat =
   Pat*
@@ -510,36 +559,3 @@ Pat =
 | RangePat
 | LiteralPat
 | MacroPat
-
-Expr =
-  TupleExpr
-| ArrayExpr
-| ParenExpr
-| PathExpr
-| LambdaExpr
-| IfExpr
-| LoopExpr
-| ForExpr
-| WhileExpr
-| ContinueExpr
-| BreakExpr
-| Label
-| BlockExpr
-| ReturnExpr
-| MatchExpr
-| RecordExpr
-| CallExpr
-| IndexExpr
-| MethodCallExpr
-| FieldExpr
-| AwaitExpr
-| TryExpr
-| EffectExpr
-| CastExpr
-| RefExpr
-| PrefixExpr
-| RangeExpr
-| BinExpr
-| Literal
-| MacroCall
-| BoxExpr