Java to Kotlin converter: special conversion of some Collections methods

j2k/src/org/jetbrains/jet/j2k/visitors/ExpressionVisitor.kt

@@ -240,6 +240,34 @@ open class ExpressionVisitor(private val converter: Converter) : JavaElementVisi
             return
         }
 
+        //TODO: type arguments maybe required if we are in initializer of variable with no explicit type
+        if (target is PsiMethod && isCollectionsEmptyList(target) && arguments.size == 0) {
+            result = MethodCallExpression.build(null, "listOf", listOf(), listOf(), false)
+            return
+        }
+
+        //TODO: type arguments maybe required if we are in initializer of variable with no explicit type
+        if (target is PsiMethod && isCollectionsEmptySet(target) && arguments.size == 0) {
+            result = MethodCallExpression.build(null, "setOf", listOf(), listOf(), false)
+            return
+        }
+
+        //TODO: type arguments maybe required if we are in initializer of variable with no explicit type
+        if (target is PsiMethod && isCollectionsEmptyMap(target) && arguments.size == 0) {
+            result = MethodCallExpression.build(null, "mapOf", listOf(), listOf(), false)
+            return
+        }
+
+        if (target is PsiMethod && isCollectionsSingletonList(target) && arguments.size == 1) {
+            result = MethodCallExpression.build(null, "listOf", listOf(converter.convertExpression(arguments.single())), listOf(), false)
+            return
+        }
+
+        if (target is PsiMethod && isCollectionsSingleton(target) && arguments.size == 1) {
+            result = MethodCallExpression.build(null, "setOf", listOf(converter.convertExpression(arguments.single())), listOf(), false)
+            return
+        }
+
         result = MethodCallExpression(converter.convertExpression(methodExpr),
                                       convertArguments(expression),
                                       typeArguments,
@@ -258,6 +286,36 @@ open class ExpressionVisitor(private val converter: Converter) : JavaElementVisi
                 method.getContainingClass()?.getQualifiedName() == "java.util.Objects"
     }
 
+    private fun isCollectionsEmptyList(method: PsiMethod): Boolean {
+        return method.getName() == "emptyList" &&
+                method.getParameterList().getParameters().size == 0 &&
+                method.getContainingClass()?.getQualifiedName() == "java.util.Collections"
+    }
+
+    private fun isCollectionsEmptySet(method: PsiMethod): Boolean {
+        return method.getName() == "emptySet" &&
+                method.getParameterList().getParameters().size == 0 &&
+                method.getContainingClass()?.getQualifiedName() == "java.util.Collections"
+    }
+
+    private fun isCollectionsEmptyMap(method: PsiMethod): Boolean {
+        return method.getName() == "emptyMap" &&
+                method.getParameterList().getParameters().size == 0 &&
+                method.getContainingClass()?.getQualifiedName() == "java.util.Collections"
+    }
+
+    private fun isCollectionsSingletonList(method: PsiMethod): Boolean {
+        return method.getName() == "singletonList" &&
+                method.getParameterList().getParameters().size == 1 &&
+                method.getContainingClass()?.getQualifiedName() == "java.util.Collections"
+    }
+
+    private fun isCollectionsSingleton(method: PsiMethod): Boolean {
+        return method.getName() == "singleton" &&
+                method.getParameterList().getParameters().size == 1 &&
+                method.getContainingClass()?.getQualifiedName() == "java.util.Collections"
+    }
+
     override fun visitNewExpression(expression: PsiNewExpression) {
         if (expression.getArrayInitializer() != null) {
             result = converter.convertExpression(expression.getArrayInitializer())

j2k/tests/test/org/jetbrains/jet/j2k/test/JavaToKotlinConverterTestGenerated.java

@@ -2050,6 +2050,11 @@ public class JavaToKotlinConverterTestGenerated extends AbstractJavaToKotlinConv
             doTest("j2k/tests/testData/ast/methodCallExpression/callWithKeywords.java");
         }
         
+        @TestMetadata("collectionsMethods.java")
+        public void testCollectionsMethods() throws Exception {
+            doTest("j2k/tests/testData/ast/methodCallExpression/collectionsMethods.java");
+        }
+        
         @TestMetadata("emptyCall.java")
         public void testEmptyCall() throws Exception {
             doTest("j2k/tests/testData/ast/methodCallExpression/emptyCall.java");

j2k/tests/testData/ast/methodCallExpression/collectionsMethods.java

@@ -0,0 +1,12 @@
+//file
+import java.util.*;
+
+class A {
+    Map<String, String> foo() {
+        List<String> list1 = Collections.emptyList();
+        List<Integer> list2 = Collections.singletonList(1);
+        Set<String> set1 = Collections.emptySet();
+        Set<String> set2 = Collections.singleton("a");
+        return Collections.emptyMap();
+    }
+}

j2k/tests/testData/ast/methodCallExpression/collectionsMethods.kt

@@ -0,0 +1,12 @@
+import java.util.*
+import kotlin.Map
+
+class A {
+    fun foo(): Map<String, String> {
+        val list1 = listOf()
+        val list2 = listOf(1)
+        val set1 = setOf()
+        val set2 = setOf("a")
+        return mapOf()
+    }
+}

j2k/tests/testData/ast/methodCallExpression/collectionsMethods.kt.todo

@@ -0,0 +1,12 @@
+import java.util.*
+import kotlin.Map
+
+class A {
+    fun foo(): Map<String, String> {
+        val list1 = listOf<String>()
+        val list2 = listOf(1)
+        val set1 = setOf<String>()
+        val set2 = setOf("a")
+        return mapOf()
+    }
+}