KT-3182 Prohibit val/var keywords at for-loop counter.

#KT-3182 fixed

compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/Errors.java

@@ -473,6 +473,8 @@ public interface Errors {
 
     DiagnosticFactory3<JetExpression, DeclarationDescriptor, Visibility, DeclarationDescriptor> INVISIBLE_SETTER = DiagnosticFactory3.create(ERROR);
 
+    DiagnosticFactory1<PsiElement, JetKeywordToken> VAL_OR_VAR_ON_LOOP_PARAMETER = DiagnosticFactory1.create(ERROR);
+
     // Backing fields
 
     SimpleDiagnosticFactory<JetElement> NO_BACKING_FIELD_ABSTRACT_PROPERTY = SimpleDiagnosticFactory.create(ERROR);

compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/rendering/DefaultErrorMessages.java

@@ -179,6 +179,8 @@ public class DefaultErrorMessages {
         MAP.put(INITIALIZATION_BEFORE_DECLARATION, "Variable cannot be initialized before declaration", NAME);
         MAP.put(VARIABLE_EXPECTED, "Variable expected");
 
+        MAP.put(VAL_OR_VAR_ON_LOOP_PARAMETER, "''{0}'' on loop parameter is not allowed", TO_STRING);
+
         MAP.put(INITIALIZATION_USING_BACKING_FIELD_CUSTOM_SETTER,
                 "This property has a custom setter, so initialization using backing field required", NAME);
         MAP.put(INITIALIZATION_USING_BACKING_FIELD_OPEN_SETTER,

compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/ControlStructureTypingVisitor.java

@@ -17,6 +17,7 @@
 package org.jetbrains.jet.lang.types.expressions;
 
 import com.google.common.collect.Lists;
+import com.intellij.lang.ASTNode;
 import com.intellij.openapi.util.Pair;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.util.PsiTreeUtil;
@@ -44,6 +45,8 @@ import org.jetbrains.jet.lang.resolve.scopes.receivers.TransientReceiver;
 import org.jetbrains.jet.lang.types.*;
 import org.jetbrains.jet.lang.types.checker.JetTypeChecker;
 import org.jetbrains.jet.lang.types.lang.KotlinBuiltIns;
+import org.jetbrains.jet.lexer.JetKeywordToken;
+import org.jetbrains.jet.lexer.JetTokens;
 import org.jetbrains.jet.util.slicedmap.WritableSlice;
 
 import java.util.ArrayList;
@@ -311,6 +314,11 @@ public class ControlStructureTypingVisitor extends ExpressionTypingVisitor {
             JetType expectedParameterType,
             ExpressionTypingContext context
     ) {
+        ASTNode valOrVarNode = loopParameter.getValOrVarNode();
+        if (valOrVarNode != null) {
+            context.trace.report(VAL_OR_VAR_ON_LOOP_PARAMETER.on(valOrVarNode.getPsi(), ((JetKeywordToken) valOrVarNode.getElementType())));
+        }
+
         JetTypeReference typeReference = loopParameter.getTypeReference();
         VariableDescriptor variableDescriptor;
         if (typeReference != null) {

compiler/testData/diagnostics/tests/controlStructures/valVarLoopParameter.kt

@@ -0,0 +1,9 @@
+fun f() {
+    for (<!VAL_OR_VAR_ON_LOOP_PARAMETER!>val<!> i in 1..4) {
+
+    }
+
+    for (<!VAL_OR_VAR_ON_LOOP_PARAMETER!>var<!> i in 1..4) {
+
+    }
+}

compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java

@@ -1045,6 +1045,11 @@ public class JetDiagnosticsTestGenerated extends AbstractDiagnosticsTestWithEage
                 doTest("compiler/testData/diagnostics/tests/controlStructures/tryReturnType.kt");
             }
             
+            @TestMetadata("valVarLoopParameter.kt")
+            public void testValVarLoopParameter() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/controlStructures/valVarLoopParameter.kt");
+            }
+            
             @TestMetadata("when.kt234.kt973.kt")
             public void testWhen_kt234_kt973() throws Exception {
                 doTest("compiler/testData/diagnostics/tests/controlStructures/when.kt234.kt973.kt");