Parse: Allow empty generic argument lists and generic argument lists containing ... in expression context

Author: slavapestov

lib/Parse/ParseExpr.cpp

@@ -1227,12 +1227,9 @@ Parser::parseExprPostfixSuffix(ParserResult<Expr> Result, bool isExprBasic,
         if (argStat.isErrorOrHasCompletion())
           diagnose(LAngleLoc, diag::while_parsing_as_left_angle_bracket);
 
-        // The result can be empty in error cases.
-        if (!args.empty()) {
-          Result = makeParserResult(
-              Result, UnresolvedSpecializeExpr::create(
-                          Context, Result.get(), LAngleLoc, args, RAngleLoc));
-        }
+        Result = makeParserResult(
+            Result, UnresolvedSpecializeExpr::create(
+                        Context, Result.get(), LAngleLoc, args, RAngleLoc));
       }
 
       continue;
@@ -2241,8 +2238,7 @@ ParserResult<Expr> Parser::parseExprIdentifier() {
     if (argStatus.isErrorOrHasCompletion())
       diagnose(LAngleLoc, diag::while_parsing_as_left_angle_bracket);
 
-    // The result can be empty in error cases.
-    hasGenericArgumentList = !args.empty();
+    hasGenericArgumentList = true;
   }
 
   if (name.getBaseName().isEditorPlaceholder()) {

lib/Parse/ParseType.cpp

@@ -1365,13 +1365,18 @@ bool Parser::canParseGenericArguments() {
   if (!startsWithLess(Tok))
     return false;
   consumeStartingLess();
-  
+
+  if (startsWithGreater(Tok)) {
+    consumeStartingGreater();
+    return true;
+  }
+
   do {
     if (!canParseType())
       return false;
     // Parse the comma, if the list continues.
   } while (consumeIf(tok::comma));
-  
+
   if (!startsWithGreater(Tok)) {
     return false;
   } else {
@@ -1454,19 +1459,20 @@ bool Parser::canParseType() {
     break;
   }
 
-  if (!isAtFunctionTypeArrow())
-    return true;
-
-  // Handle type-function if we have an '->' with optional
-  // 'async' and/or 'throws'.
-  while (isEffectsSpecifier(Tok))
-    consumeToken();
+  if (isAtFunctionTypeArrow()) {
+    // Handle type-function if we have an '->' with optional
+    // 'async' and/or 'throws'.
+    while (isEffectsSpecifier(Tok))
+      consumeToken();
 
-  if (!consumeIf(tok::arrow))
-    return false;
-  
-  if (!canParseType())
-    return false;
+    if (!consumeIf(tok::arrow))
+      return false;
+    
+    if (!canParseType())
+      return false;
+    
+    return true;
+  }
 
   // Parse pack expansion 'T...'.
   if (Tok.isEllipsis()) {