Temporary parse label definitions with both syntax versions

Should be reverted after bootstrap

compiler/frontend/src/org/jetbrains/kotlin/parsing/JetExpressionParsing.java

@@ -554,10 +554,15 @@ public class JetExpressionParsing extends AbstractJetParsing {
             return lookahead(2) == LBRACE;
         }
 
+        if (at(AT) && myBuilder.rawLookup(1) == IDENTIFIER) {
+            return lookahead(2) == LBRACE;
+        }
+
         return at(AT) && lookahead(1) == LBRACE;
     }
 
     private boolean isAtLabelDefinitionOrMissingIdentifier() {
+        if (at(AT) && myBuilder.rawLookup(1) == IDENTIFIER) return true;
         return (at(IDENTIFIER) && myBuilder.rawLookup(1) == AT) || at(AT);
     }
 
@@ -1659,8 +1664,22 @@ public class JetExpressionParsing extends AbstractJetParsing {
      */
     private void parseLabelDefinition() {
         if (at(AT)) {
-            // recovery for empty label identifier
+            // recovery for old label syntax or empty label identifier
+            if (myBuilder.rawLookup(1) == IDENTIFIER) {
+                PsiBuilder.Marker labelWrap = mark();
+                PsiBuilder.Marker mark = mark();
+
+                advance(); // AT
+                advance(); // IDENTIFIER
+
+                mark.done(LABEL);
+
+                labelWrap.done(LABEL_QUALIFIER);
+                return;
+            }
+            else {
                 errorAndAdvance("Label must be named"); // AT
+            }
             return;
         }
 

compiler/testData/psi/newLabels/oldSyntaxExpressions.txt

@@ -13,12 +13,10 @@ JetFile: oldSyntaxExpressions.kt
       PsiElement(LBRACE)('{')
       PsiWhiteSpace('\n    ')
       LABELED_EXPRESSION
-        PsiErrorElement:Label must be named
+        LABEL_QUALIFIER
+          LABEL
             PsiElement(AT)('@')
-        REFERENCE_EXPRESSION
             PsiElement(IDENTIFIER)('loop1')
-      PsiErrorElement:Unexpected tokens (use ';' to separate expressions on the same line)
-        <empty list>
         PsiWhiteSpace(' ')
         FOR
           PsiElement(for)('for')
@@ -49,10 +47,14 @@ JetFile: oldSyntaxExpressions.kt
         REFERENCE_EXPRESSION
           PsiElement(IDENTIFIER)('x2')
         PsiElement(DOT)('.')
+        CALL_EXPRESSION
           REFERENCE_EXPRESSION
             PsiElement(IDENTIFIER)('filter')
           PsiWhiteSpace(' ')
-      PsiErrorElement:Unexpected tokens (use ';' to separate expressions on the same line)
+          FUNCTION_LITERAL_ARGUMENT
+            LABELED_EXPRESSION
+              LABEL_QUALIFIER
+                LABEL
                   PsiElement(AT)('@')
                   PsiElement(IDENTIFIER)('f')
               PsiWhiteSpace(' ')
@@ -75,14 +77,12 @@ JetFile: oldSyntaxExpressions.kt
         PARENTHESIZED
           PsiElement(LPAR)('(')
           LABELED_EXPRESSION
-            PsiErrorElement:Label must be named
+            LABEL_QUALIFIER
+              LABEL
                 PsiElement(AT)('@')
-            REFERENCE_EXPRESSION
                 PsiElement(IDENTIFIER)('f')
-          PsiErrorElement:Expecting ')'
-            <empty list>
             PsiWhiteSpace(' ')
-      PsiErrorElement:Unexpected tokens (use ';' to separate expressions on the same line)
+            INTEGER_CONSTANT
               PsiElement(INTEGER_LITERAL)('3')
           PsiElement(RPAR)(')')
       PsiWhiteSpace('\n\n    ')

compiler/testData/psi/newLabels/recovery.txt

@@ -123,12 +123,12 @@ JetFile: recovery.kt
               PsiElement(return)('return')
             PsiWhiteSpace('\n        ')
             LABELED_EXPRESSION
-              PsiErrorElement:Label must be named
+              LABEL_QUALIFIER
+                LABEL
                   PsiElement(AT)('@')
-              REFERENCE_EXPRESSION
                   PsiElement(IDENTIFIER)('loop2')
               PsiWhiteSpace(' ')
-            PsiErrorElement:Unexpected tokens (use ';' to separate expressions on the same line)
+              INTEGER_CONSTANT
                 PsiElement(INTEGER_LITERAL)('4')
           PsiWhiteSpace('\n    ')
           PsiElement(RBRACE)('}')

compiler/testData/psi/newLabels/spaceBeforeLabelReference.txt

@@ -33,12 +33,12 @@ JetFile: spaceBeforeLabelReference.kt
         PsiElement(return)('return')
         PsiWhiteSpace(' ')
         LABELED_EXPRESSION
-          PsiErrorElement:Label must be named
+          LABEL_QUALIFIER
+            LABEL
               PsiElement(AT)('@')
-          REFERENCE_EXPRESSION
               PsiElement(IDENTIFIER)('l2')
           PsiWhiteSpace(' ')
-      PsiErrorElement:Unexpected tokens (use ';' to separate expressions on the same line)
+          INTEGER_CONSTANT
             PsiElement(INTEGER_LITERAL)('1')
       PsiWhiteSpace('\n\n    ')
       PROPERTY
@@ -55,9 +55,9 @@ JetFile: spaceBeforeLabelReference.kt
         PsiElement(return)('return')
         PsiWhiteSpace(' ')
         LABELED_EXPRESSION
-          PsiErrorElement:Label must be named
+          LABEL_QUALIFIER
+            LABEL
               PsiElement(AT)('@')
-          REFERENCE_EXPRESSION
               PsiElement(IDENTIFIER)('l3')
           PsiWhiteSpace('\n\n    ')
           PROPERTY
@@ -111,9 +111,9 @@ JetFile: spaceBeforeLabelReference.kt
         PsiWhiteSpace(' ')
         PsiComment(BLOCK_COMMENT)('/**/')
         LABELED_EXPRESSION
-          PsiErrorElement:Label must be named
+          LABEL_QUALIFIER
+            LABEL
               PsiElement(AT)('@')
-          REFERENCE_EXPRESSION
               PsiElement(IDENTIFIER)('l6')
           PsiWhiteSpace('\n\n    ')
           PROPERTY
@@ -131,12 +131,12 @@ JetFile: spaceBeforeLabelReference.kt
       PsiComment(EOL_COMMENT)('//')
       PsiWhiteSpace('\n')
       LABELED_EXPRESSION
-        PsiErrorElement:Label must be named
+        LABEL_QUALIFIER
+          LABEL
             PsiElement(AT)('@')
-        REFERENCE_EXPRESSION
             PsiElement(IDENTIFIER)('l7')
         PsiWhiteSpace(' ')
-      PsiErrorElement:Unexpected tokens (use ';' to separate expressions on the same line)
+        INTEGER_CONSTANT
           PsiElement(INTEGER_LITERAL)('4')
       PsiWhiteSpace('\n\n    ')
       PROPERTY