Name suggester: Improve name suggestion strategy for type parameters

idea/src/org/jetbrains/jet/plugin/quickfix/createFromUsage/callableBuilder/CallableBuilder.kt

@@ -330,17 +330,20 @@ class CallableBuilder(val config: CallableBuilderConfiguration) {
                     CallableMemberDescriptor.Kind.SYNTHESIZED,
                     SourceElement.NO_SOURCE
             )
+
             val validator = CollectingValidator { scope.getClassifier(Name.identifier(it)) == null }
+            val parameterNames = JetNameSuggester.suggestNamesForTypeParameters(typeParameterCount, validator)
             val typeParameters = typeParameterCount.indices.map {
                 TypeParameterDescriptorImpl.createWithDefaultBound(
                         fakeFunction,
                         Annotations.EMPTY,
                         false,
                         Variance.INVARIANT,
-                        Name.identifier(validator.validateName("T")),
+                        Name.identifier(parameterNames[it]),
                         it
                 )
             }
+
             return fakeFunction.initialize(null, null, typeParameters, Collections.emptyList(), null, null, Visibilities.INTERNAL)
         }
 

idea/src/org/jetbrains/jet/plugin/refactoring/JetNameSuggester.java

@@ -22,6 +22,7 @@ import com.intellij.util.ArrayUtil;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.jet.lang.descriptors.ClassDescriptor;
+import org.jetbrains.jet.lang.descriptors.ClassifierDescriptor;
 import org.jetbrains.jet.lang.psi.*;
 import org.jetbrains.jet.lang.resolve.BindingContext;
 import org.jetbrains.jet.lang.resolve.name.Name;
@@ -96,6 +97,16 @@ public class JetNameSuggester {
         return ArrayUtil.toStringArray(result);
     }
 
+    private static final String[] COMMON_TYPE_PARAMETER_NAMES = {"T", "U", "V", "W", "X", "Y", "Z"};
+
+    public static @NotNull String[] suggestNamesForTypeParameters(int count, @NotNull JetNameValidator validator) {
+        ArrayList<String> result = new ArrayList<String>();
+        for (int i = 0; i < count; i++) {
+            result.add(validator.validateNameWithVariants(COMMON_TYPE_PARAMETER_NAMES));
+        }
+        return ArrayUtil.toStringArray(result);
+    }
+
     private static void addNamesForType(ArrayList<String> result, JetType jetType, JetNameValidator validator) {
         KotlinBuiltIns builtIns = KotlinBuiltIns.getInstance();
         JetTypeChecker typeChecker = JetTypeChecker.DEFAULT;

idea/src/org/jetbrains/jet/plugin/refactoring/JetNameValidator.kt

@@ -35,6 +35,23 @@ public abstract class JetNameValidator {
         return name + i
     }
 
+    /**
+     * Validates name using set of variants which are tried in succession (and extended with suffixes if necessary)
+     * For example, when given sequence of a, b, c possible names are tried out in the following order: a, b, c, a1, b1, c1, a2, b2, c2, ...
+     * @param names to check it in scope
+     * @return name or nameI, where name is one of variants and I is a number
+     */
+    public fun validateNameWithVariants(vararg names: String): String {
+        var i = 0
+        while (true) {
+            for (name in names) {
+                val candidate = if (i > 0) name + i else name
+                if (validateInner(candidate)) return candidate
+            }
+            i++
+        }
+    }
+
     protected abstract fun validateInner(name: String): Boolean
 }
 
@@ -48,12 +65,12 @@ public open class CollectingValidator(
 ): JetNameValidator() {
     private val suggestedSet = HashSet(existingNames)
 
-    override fun validateInner(name: String): Boolean = name !in suggestedSet && filter(name)
-
-    override fun validateName(name: String): String {
-        val validatedName = super.validateName(name)
-        suggestedSet.add(validatedName)
-        return validatedName
+    override fun validateInner(name: String): Boolean {
+        if (name !in suggestedSet && filter(name)) {
+            suggestedSet.add(name)
+            return true
+        }
+        return false
     }
 }
 

idea/testData/quickfix/createFromUsage/createFunction/call/typeArguments/afterClassMember.kt

@@ -1,7 +1,7 @@
 // "Create function 'foo'" "true"
 
 class B<T>(val t: T) {
-    fun <T1, T2> foo(arg: T1, arg1: T2): T1 {
+    fun <U, V> foo(arg: U, arg1: V): U {
         throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 

idea/testData/quickfix/createFromUsage/createFunction/call/typeArguments/afterClassMemberPartialSubstitution.kt

@@ -1,7 +1,7 @@
 // "Create function 'foo'" "true"
 
 class B<T>(val t: T) {
-    fun <T1> foo(i: Int, arg: T1): Int {
+    fun <U> foo(i: Int, arg: U): Int {
         throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 

idea/testData/quickfix/createFromUsage/createFunction/call/typeArguments/afterClassMemberWithReceiverArg.kt

@@ -1,7 +1,7 @@
 // "Create function 'foo'" "true"
 
 class B<T>(val t: T) {
-    fun <T1, T2> foo(arg: T1, arg1: T2): T1 {
+    fun <U, V> foo(arg: U, arg1: V): U {
         throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 

idea/testData/quickfix/createFromUsage/createFunction/call/typeArguments/afterExtension.kt

@@ -6,6 +6,6 @@ class A<T>(val items: List<T>) {
     }
 }
 
-fun <E, T, T1> List<E>.foo(arg: T, arg1: T1): T {
+fun <E, T, U> List<E>.foo(arg: T, arg1: U): T {
     throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
 }

idea/testData/quickfix/createFromUsage/createFunction/call/typeArguments/afterExtensionWithReceiverArg.kt

@@ -6,6 +6,6 @@ class A<T>(val items: List<T>) {
     }
 }
 
-fun <E, T, T1> List<E>.foo(arg: T, arg1: T1): T {
+fun <E, T, U> List<E>.foo(arg: T, arg1: U): T {
     throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
 }

idea/testData/quickfix/createFromUsage/createFunction/call/typeArguments/afterNoReceiver.kt

@@ -4,6 +4,6 @@ fun test(): Int {
     return foo<String, Int>(2, "2")
 }
 
-fun <T, T1> foo(arg: T1, arg1: T): T1 {
+fun <T, U> foo(arg: U, arg1: T): U {
     throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
 }

idea/testData/quickfix/createFromUsage/createFunction/call/typeArguments/afterNoReceiverExtraArgs.kt

@@ -4,6 +4,6 @@ fun test(): Int {
     return foo<String, Int, Boolean>(2, "2")
 }
 
-fun <T, T1, T2> foo(arg: T1, arg1: T): T1 {
+fun <T, U, V> foo(arg: U, arg1: T): U {
     throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
 }

idea/testData/quickfix/createFromUsage/createFunction/call/typeArguments/afterNoReceiverLongName.kt

@@ -4,6 +4,6 @@ fun test(): Int {
     return foo<String, Int>(2, "2")
 }
 
-fun <T, T1> foo(arg: T1, arg1: T): T1 {
+fun <T, U> foo(arg: U, arg1: T): U {
     throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
 }