Smart completion for for loop range to use loop variable type if defined

idea/src/org/jetbrains/kotlin/idea/completion/smart/SmartCompletion.kt

@@ -377,14 +377,23 @@ class SmartCompletion(
         val smartCastTypes: (VariableDescriptor) -> Collection<JetType> = TypesWithSmartCasts(bindingContext).calculate(expressionWithType, receiver)
 
         val scope = bindingContext.get(BindingContext.RESOLUTION_SCOPE, expressionWithType)
-        val iterableDetector = IterableTypesDetector(project, moduleDescriptor, scope)
+
+        val loopVar = forExpression.getLoopParameter()
+        val loopVarType = if (loopVar != null && loopVar.getTypeReference() != null) {
+            val type = (resolutionFacade.resolveToDescriptor(loopVar) as VariableDescriptor).getType()
+            if (type.isError()) null else type
+        }
+        else {
+            null
+        }
+
+        val iterableDetector = IterableTypesDetector(project, moduleDescriptor, scope, loopVarType)
 
         fun filterDeclaration(descriptor: DeclarationDescriptor): Collection<LookupElement> {
             val types = descriptor.fuzzyTypes(smartCastTypes)
 
             fun createLookupElement() = lookupElementFactory.createLookupElement(descriptor, resolutionFacade, bindingContext, true)
 
-            //TODO: use type of variable if declared
             if (types.any { iterableDetector.isIterable(it.type) }) {
                 return listOf(createLookupElement().addTail(Tail.RPARENTH))
             }

idea/src/org/jetbrains/kotlin/idea/liveTemplates/macro/BaseJetVariableMacro.java

@@ -71,7 +71,7 @@ public abstract class BaseJetVariableMacro extends Macro {
             return null;
         }
 
-        IterableTypesDetector iterableTypesDetector = new IterableTypesDetector(project, analysisResult.getModuleDescriptor(), scope);
+        IterableTypesDetector iterableTypesDetector = new IterableTypesDetector(project, analysisResult.getModuleDescriptor(), scope, null);
 
         DataFlowInfo dataFlowInfo = getDataFlowInfo(bindingContext, contextExpression);
 

idea/src/org/jetbrains/kotlin/idea/util/IterableTypesDetector.kt

@@ -34,7 +34,9 @@ import org.jetbrains.kotlin.types.typeUtil.isSubtypeOf
 public class IterableTypesDetector(
         private val project: Project,
         private val moduleDescriptor: ModuleDescriptor,
-        private val scope: JetScope) {
+        private val scope: JetScope,
+        private val loopVarType: JetType? = null
+) {
 
     private val injector = InjectorForMacros(project, moduleDescriptor)
     private val cache = HashMap<JetType, Boolean>()
@@ -56,7 +58,9 @@ public class IterableTypesDetector(
         val expression = JetPsiFactory(project).createExpression("fake")
         val expressionReceiver = ExpressionReceiver(expression, type)
         val context = ExpressionTypingContext.newContext(injector.getExpressionTypingServices(), BindingTraceContext(), scope, DataFlowInfo.EMPTY, TypeUtils.NO_EXPECTED_TYPE)
-        return injector.getExpressionTypingComponents().getForLoopConventionsChecker().checkIterableConvention(expressionReceiver, context) != null
+        val elementType = injector.getExpressionTypingComponents().getForLoopConventionsChecker().checkIterableConvention(expressionReceiver, context)
+        if (elementType == null) return false
+        return loopVarType == null || elementType.isSubtypeOf(loopVarType)
     }
 
     private fun canBeIterable(type: JetType): Boolean {

idea/testData/completion/smart/forLoopRange/TypedLoopVar.kt

@@ -0,0 +1,8 @@
+fun foo(p1: Collection<String>, p2: Collection<Int>, p3: Collection<String?>) {
+    for (i: Any in <caret>)
+}
+
+// EXIST: p1
+// EXIST: p2
+// ABSENT: p3
+// EXIST: { lookupString:"listOf", itemText: "listOf", tailText: "(vararg values: T) (kotlin)", typeText:"List<T>" }

idea/tests/org/jetbrains/kotlin/completion/JvmSmartCompletionTestGenerated.java

@@ -980,5 +980,11 @@ public class JvmSmartCompletionTestGenerated extends AbstractJvmSmartCompletionT
             String fileName = JetTestUtils.navigationMetadata("idea/testData/completion/smart/forLoopRange/SmartCasts.kt");
             doTest(fileName);
         }
+
+        @TestMetadata("TypedLoopVar.kt")
+        public void testTypedLoopVar() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/testData/completion/smart/forLoopRange/TypedLoopVar.kt");
+            doTest(fileName);
+        }
     }
 }