Do not remove trivial substitutions

to avoid substituting a new type parameter by default instead of leaving the same
 #KT-4887 Fixed

compiler/testData/diagnostics/tests/substitutions/kt4887.kt

@@ -0,0 +1,8 @@
+package h
+
+public class MyClass<S, T>(param: MyClass<S, T>) {
+    fun test() {
+        val result: MyClass<Any, Any>? = null
+        MyClass<S, Any>(result <!CAST_NEVER_SUCCEEDS!>as<!> MyClass<S, Any>)
+    }
+}

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

@@ -6773,6 +6773,11 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest("compiler/testData/diagnostics/tests/substitutions/kt1558-short.kt");
             }
             
+            @TestMetadata("kt4887.kt")
+            public void testKt4887() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/substitutions/kt4887.kt");
+            }
+            
             @TestMetadata("upperBoundsSubstitutionForOverloadResolutionWithAmbiguity.kt")
             public void testUpperBoundsSubstitutionForOverloadResolutionWithAmbiguity() throws Exception {
                 doTest("compiler/testData/diagnostics/tests/substitutions/upperBoundsSubstitutionForOverloadResolutionWithAmbiguity.kt");

core/descriptors/src/org/jetbrains/jet/lang/descriptors/impl/AbstractClassDescriptor.java

@@ -116,10 +116,7 @@ public abstract class AbstractClassDescriptor implements ClassDescriptor {
         List<TypeParameterDescriptor> typeParameters = getTypeConstructor().getParameters();
         Map<TypeConstructor, TypeProjection> substitutionContext = TypeSubstitutor.buildSubstitutionContext(typeParameters, typeArguments);
 
-        // Unsafe substitutor is OK, because no recursion can hurt us upon a trivial substitution:
-        // all the types are written explicitly in the code already, they can not get infinite.
-        // One exception is *-projections, but they need to be handled separately anyways.
-        TypeSubstitutor substitutor = TypeSubstitutor.createUnsafe(substitutionContext);
+        TypeSubstitutor substitutor = TypeSubstitutor.create(substitutionContext);
         return new SubstitutingScope(getScopeForMemberLookup(), substitutor);
     }
 

core/descriptors/src/org/jetbrains/jet/lang/types/TypeSubstitutor.java

@@ -25,7 +25,6 @@ import org.jetbrains.jet.lang.resolve.scopes.SubstitutingScope;
 import org.jetbrains.jet.lang.types.lang.KotlinBuiltIns;
 
 import java.util.HashMap;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 
@@ -72,14 +71,8 @@ public class TypeSubstitutor {
         return create(new CompositeTypeSubstitution(substitutions));
     }
 
-    /** No assertion for immediate recursion */
-    public static TypeSubstitutor createUnsafe(@NotNull Map<TypeConstructor, TypeProjection> substitutionContext) {
-        Map<TypeConstructor, TypeProjection> cleanContext = removeTrivialSubstitutions(substitutionContext);
-        return create(new MapToTypeSubstitutionAdapter(cleanContext));
-    }
-
     public static TypeSubstitutor create(@NotNull Map<TypeConstructor, TypeProjection> substitutionContext) {
-        return createUnsafe(removeTrivialSubstitutions(substitutionContext));
+        return create(new MapToTypeSubstitutionAdapter(substitutionContext));
     }
 
     public static TypeSubstitutor create(@NotNull JetType context) {
@@ -226,22 +219,6 @@ public class TypeSubstitutor {
         return substitutedArguments;
     }
 
-    @NotNull
-    private static Map<TypeConstructor, TypeProjection> removeTrivialSubstitutions(@NotNull Map<TypeConstructor, TypeProjection> context) {
-        Map<TypeConstructor, TypeProjection> clean = new HashMap<TypeConstructor, TypeProjection>(context);
-        boolean changed = false;
-        for (Iterator<Map.Entry<TypeConstructor, TypeProjection>> iterator = clean.entrySet().iterator(); iterator.hasNext(); ) {
-            Map.Entry<TypeConstructor, TypeProjection> entry = iterator.next();
-            TypeConstructor key = entry.getKey();
-            TypeProjection value = entry.getValue();
-            if (key == value.getType().getConstructor() && value.getProjectionKind() == Variance.INVARIANT) {
-                iterator.remove();
-                changed = true;
-            }
-        }
-        return changed ? clean : context;
-    }
-
     private static Variance combine(Variance typeParameterVariance, Variance projectionKind) {
         if (typeParameterVariance == Variance.INVARIANT) return projectionKind;
         if (projectionKind == Variance.INVARIANT) return typeParameterVariance;