understand "interface" keyword as synonym for "trait"

compiler/frontend/src/org/jetbrains/kotlin/lexer/JetTokens.java

@@ -73,6 +73,7 @@ public interface JetTokens {
     JetKeywordToken DO_KEYWORD               = JetKeywordToken.keyword("do");
     JetKeywordToken WHEN_KEYWORD             = JetKeywordToken.keyword("when");
     JetKeywordToken TRAIT_KEYWORD            = JetKeywordToken.keyword("trait");
+    JetKeywordToken INTERFACE_KEYWORD        = JetKeywordToken.keyword("interface");
     // TODO: Discuss "This" keyword
     JetKeywordToken CAPITALIZED_THIS_KEYWORD = JetKeywordToken.keyword("This");
 
@@ -160,7 +161,7 @@ public interface JetTokens {
     JetKeywordToken FINALLY_KEYWORD   = JetKeywordToken.softKeyword("finally");
     JetModifierKeywordToken FINAL_KEYWORD     = JetModifierKeywordToken.softKeywordModifier("final");
 
-    TokenSet KEYWORDS = TokenSet.create(PACKAGE_KEYWORD, AS_KEYWORD, TYPE_ALIAS_KEYWORD, CLASS_KEYWORD, TRAIT_KEYWORD,
+    TokenSet KEYWORDS = TokenSet.create(PACKAGE_KEYWORD, AS_KEYWORD, TYPE_ALIAS_KEYWORD, CLASS_KEYWORD, TRAIT_KEYWORD, INTERFACE_KEYWORD,
                                         THIS_KEYWORD, SUPER_KEYWORD, VAL_KEYWORD, VAR_KEYWORD, FUN_KEYWORD, FOR_KEYWORD,
                                         NULL_KEYWORD,
                                         TRUE_KEYWORD, FALSE_KEYWORD, IS_KEYWORD,

compiler/frontend/src/org/jetbrains/kotlin/lexer/Kotlin.flex

@@ -241,6 +241,7 @@ LONG_TEMPLATE_ENTRY_START=\$\{
 {CHARACTER_LITERAL} { return JetTokens.CHARACTER_LITERAL; }
 
 "typealias"  { return JetTokens.TYPE_ALIAS_KEYWORD ;}
+"interface"  { return JetTokens.INTERFACE_KEYWORD ;}
 "continue"   { return JetTokens.CONTINUE_KEYWORD ;}
 "package"    { return JetTokens.PACKAGE_KEYWORD ;}
 "return"     { return JetTokens.RETURN_KEYWORD ;}

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

@@ -53,7 +53,7 @@ public class JetExpressionParsing extends AbstractJetParsing {
 
     private static final TokenSet TYPE_ARGUMENT_LIST_STOPPERS = TokenSet.create(
             INTEGER_LITERAL, FLOAT_LITERAL, CHARACTER_LITERAL, OPEN_QUOTE,
-            PACKAGE_KEYWORD, AS_KEYWORD, TYPE_ALIAS_KEYWORD, TRAIT_KEYWORD, CLASS_KEYWORD, THIS_KEYWORD, VAL_KEYWORD, VAR_KEYWORD,
+            PACKAGE_KEYWORD, AS_KEYWORD, TYPE_ALIAS_KEYWORD, TRAIT_KEYWORD, INTERFACE_KEYWORD, CLASS_KEYWORD, THIS_KEYWORD, VAL_KEYWORD, VAR_KEYWORD,
             FUN_KEYWORD, FOR_KEYWORD, NULL_KEYWORD,
             TRUE_KEYWORD, FALSE_KEYWORD, IS_KEYWORD, THROW_KEYWORD, RETURN_KEYWORD, BREAK_KEYWORD,
             CONTINUE_KEYWORD, OBJECT_KEYWORD, IF_KEYWORD, TRY_KEYWORD, ELSE_KEYWORD, WHILE_KEYWORD, DO_KEYWORD,
@@ -124,6 +124,7 @@ public class JetExpressionParsing extends AbstractJetParsing {
                     FUN_KEYWORD,
                     VAL_KEYWORD, VAR_KEYWORD,
                     TRAIT_KEYWORD,
+                    INTERFACE_KEYWORD,
                     CLASS_KEYWORD,
                     TYPE_ALIAS_KEYWORD
             ),
@@ -1336,7 +1337,7 @@ public class JetExpressionParsing extends AbstractJetParsing {
     private IElementType parseLocalDeclarationRest(boolean isEnum) {
         IElementType keywordToken = tt();
         IElementType declType = null;
-        if (keywordToken == CLASS_KEYWORD || keywordToken == TRAIT_KEYWORD) {
+        if (keywordToken == CLASS_KEYWORD || keywordToken == TRAIT_KEYWORD || keywordToken == INTERFACE_KEYWORD) {
             declType = myJetParsing.parseClass(isEnum);
         }
         else if (keywordToken == FUN_KEYWORD) {

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

@@ -44,9 +44,9 @@ public class JetParsing extends AbstractJetParsing {
         }
     }
 
-    private static final TokenSet TOPLEVEL_OBJECT_FIRST = TokenSet.create(TYPE_ALIAS_KEYWORD, TRAIT_KEYWORD, CLASS_KEYWORD,
+    private static final TokenSet TOPLEVEL_OBJECT_FIRST = TokenSet.create(TYPE_ALIAS_KEYWORD, TRAIT_KEYWORD, INTERFACE_KEYWORD, CLASS_KEYWORD,
                 FUN_KEYWORD, VAL_KEYWORD, PACKAGE_KEYWORD);
-    private static final TokenSet ENUM_MEMBER_FIRST = TokenSet.create(TYPE_ALIAS_KEYWORD, TRAIT_KEYWORD, CLASS_KEYWORD,
+    private static final TokenSet ENUM_MEMBER_FIRST = TokenSet.create(TYPE_ALIAS_KEYWORD, TRAIT_KEYWORD, INTERFACE_KEYWORD, CLASS_KEYWORD,
                 FUN_KEYWORD, VAL_KEYWORD, LBRACE, IDENTIFIER, OBJECT_KEYWORD);
 
     private static final TokenSet CLASS_NAME_RECOVERY_SET = TokenSet.orSet(TokenSet.create(LT, LPAR, COLON, LBRACE), TOPLEVEL_OBJECT_FIRST);
@@ -380,7 +380,7 @@ public class JetParsing extends AbstractJetParsing {
 //            declType = parsePackageBlock();
 //        }
 //        else
-        if (keywordToken == CLASS_KEYWORD || keywordToken == TRAIT_KEYWORD) {
+        if (keywordToken == CLASS_KEYWORD || keywordToken == TRAIT_KEYWORD || keywordToken == INTERFACE_KEYWORD) {
             declType = parseClass(detector.isEnumDetected());
         }
         else if (keywordToken == FUN_KEYWORD) {
@@ -577,7 +577,7 @@ public class JetParsing extends AbstractJetParsing {
 
     /*
      * class
-     *   : modifiers ("class" | "trait") SimpleName
+     *   : modifiers ("class" | "interface") SimpleName
      *       typeParameters?
      *         modifiers ("(" primaryConstructorParameter{","} ")")?
      *       (":" annotations delegationSpecifier{","})?
@@ -594,7 +594,7 @@ public class JetParsing extends AbstractJetParsing {
             assert _at(OBJECT_KEYWORD);
         }
         else {
-            assert _atSet(CLASS_KEYWORD, TRAIT_KEYWORD);
+            assert _atSet(CLASS_KEYWORD, TRAIT_KEYWORD, INTERFACE_KEYWORD);
         }
         advance(); // CLASS_KEYWORD, TRAIT_KEYWORD or OBJECT_KEYWORD
 
@@ -823,7 +823,7 @@ public class JetParsing extends AbstractJetParsing {
         if (keywordToken == CLASS_KEYWORD) {
             declType = parseClass(isEnum);
         }
-        else if (keywordToken == TRAIT_KEYWORD) {
+        else if (keywordToken == TRAIT_KEYWORD || keywordToken == INTERFACE_KEYWORD) {
             declType = parseClass(isEnum);
         }
         else if (keywordToken == FUN_KEYWORD) {

compiler/frontend/src/org/jetbrains/kotlin/psi/JetClass.java

@@ -27,10 +27,8 @@ import com.intellij.util.IncorrectOperationException;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.kotlin.JetNodeTypes;
-import org.jetbrains.kotlin.lexer.JetModifierKeywordToken;
 import org.jetbrains.kotlin.lexer.JetTokens;
 import org.jetbrains.kotlin.name.FqName;
-import org.jetbrains.kotlin.psi.addRemoveModifier.AddRemoveModifierPackage;
 import org.jetbrains.kotlin.psi.stubs.KotlinClassStub;
 import org.jetbrains.kotlin.psi.stubs.elements.JetStubElementTypes;
 
@@ -140,7 +138,8 @@ public class JetClass extends JetTypeParameterListOwnerStub<KotlinClassStub> imp
             return stub.isTrait();
         }
 
-        return findChildByType(JetTokens.TRAIT_KEYWORD) != null;
+        return findChildByType(JetTokens.TRAIT_KEYWORD) != null ||
+               findChildByType(JetTokens.INTERFACE_KEYWORD) != null;
     }
 
     public boolean isEnum() {

compiler/testData/psi/Interface.kt

@@ -0,0 +1,4 @@
+interface Foo {
+  fun f()
+  val a
+}

compiler/testData/psi/Interface.txt

@@ -0,0 +1,25 @@
+JetFile: Interface.kt
+  PACKAGE_DIRECTIVE
+    <empty list>
+  CLASS
+    PsiElement(interface)('interface')
+    PsiWhiteSpace(' ')
+    PsiElement(IDENTIFIER)('Foo')
+    PsiWhiteSpace(' ')
+    CLASS_BODY
+      PsiElement(LBRACE)('{')
+      PsiWhiteSpace('\n  ')
+      FUN
+        PsiElement(fun)('fun')
+        PsiWhiteSpace(' ')
+        PsiElement(IDENTIFIER)('f')
+        VALUE_PARAMETER_LIST
+          PsiElement(LPAR)('(')
+          PsiElement(RPAR)(')')
+      PsiWhiteSpace('\n  ')
+      PROPERTY
+        PsiElement(val)('val')
+        PsiWhiteSpace(' ')
+        PsiElement(IDENTIFIER)('a')
+      PsiWhiteSpace('\n')
+      PsiElement(RBRACE)('}')

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

@@ -355,6 +355,12 @@ public class JetParsingTestGenerated extends AbstractJetParsingTest {
             doParsingTest(fileName);
         }
 
+        @TestMetadata("Interface.kt")
+        public void testInterface() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("compiler/testData/psi/Interface.kt");
+            doParsingTest(fileName);
+        }
+
         @TestMetadata("Labels.kt")
         public void testLabels() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/psi/Labels.kt");