Change parser error for when (KT-6420)

#KT-6420 Fixed

compiler/frontend/src/org/jetbrains/jet/lang/parsing/JetExpressionParsing.java

@@ -847,7 +847,7 @@ public class JetExpressionParsing extends AbstractJetParsing {
             advance(); // COMMA
         }
 
-        expect(ARROW, "Expecting '->' or 'when'", WHEN_CONDITION_RECOVERY_SET);
+        expect(ARROW, "Expecting '->'", WHEN_CONDITION_RECOVERY_SET);
         if (atSet(WHEN_CONDITION_RECOVERY_SET)) {
             error("Expecting an element");
         }

compiler/testData/psi/recovery/NoArrowInWhen.kt

@@ -0,0 +1,5 @@
+fun test() {
+    when(element) {
+        is JetProperty when { }
+    }
+}

compiler/testData/psi/recovery/NoArrowInWhen.txt

@@ -0,0 +1,43 @@
+JetFile: NoArrowInWhen.kt
+  PACKAGE_DIRECTIVE
+    <empty list>
+  FUN
+    PsiElement(fun)('fun')
+    PsiWhiteSpace(' ')
+    PsiElement(IDENTIFIER)('test')
+    VALUE_PARAMETER_LIST
+      PsiElement(LPAR)('(')
+      PsiElement(RPAR)(')')
+    PsiWhiteSpace(' ')
+    BLOCK
+      PsiElement(LBRACE)('{')
+      PsiWhiteSpace('\n    ')
+      WHEN
+        PsiElement(when)('when')
+        PsiElement(LPAR)('(')
+        REFERENCE_EXPRESSION
+          PsiElement(IDENTIFIER)('element')
+        PsiElement(RPAR)(')')
+        PsiWhiteSpace(' ')
+        PsiElement(LBRACE)('{')
+        PsiWhiteSpace('\n        ')
+        WHEN_ENTRY
+          WHEN_CONDITION_IS_PATTERN
+            PsiElement(is)('is')
+            PsiWhiteSpace(' ')
+            TYPE_REFERENCE
+              USER_TYPE
+                REFERENCE_EXPRESSION
+                  PsiElement(IDENTIFIER)('JetProperty')
+          PsiWhiteSpace(' ')
+          PsiErrorElement:Expecting '->'
+            PsiElement(when)('when')
+          PsiWhiteSpace(' ')
+          BLOCK
+            PsiElement(LBRACE)('{')
+            PsiWhiteSpace(' ')
+            PsiElement(RBRACE)('}')
+        PsiWhiteSpace('\n    ')
+        PsiElement(RBRACE)('}')
+      PsiWhiteSpace('\n')
+      PsiElement(RBRACE)('}')

compiler/tests/org/jetbrains/jet/parsing/JetParsingTestGenerated.java

@@ -1395,6 +1395,12 @@ public class JetParsingTestGenerated extends AbstractJetParsingTest {
                 doParsingTest(fileName);
             }
 
+            @TestMetadata("NoArrowInWhen.kt")
+            public void testNoArrowInWhen() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/psi/recovery/NoArrowInWhen.kt");
+                doParsingTest(fileName);
+            }
+
             @TestMetadata("PackageNewLineRecovery.kt")
             public void testPackageNewLineRecovery() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/psi/recovery/PackageNewLineRecovery.kt");