Made parameter of renderType() @NotNull.

compiler/frontend/src/org/jetbrains/jet/renderer/DescriptorRenderer.java

@@ -45,7 +45,7 @@ public interface DescriptorRenderer extends Renderer<DeclarationDescriptor> {
     DescriptorRenderer HTML = new DescriptorRendererBuilder().setTextFormat(TextFormat.HTML).build();
 
     @NotNull
-    String renderType(@Nullable JetType type);
+    String renderType(@NotNull JetType type);
 
     @NotNull
     @Override

compiler/frontend/src/org/jetbrains/jet/renderer/DescriptorRendererImpl.java

@@ -21,7 +21,6 @@ import com.google.common.collect.Sets;
 import com.intellij.openapi.util.text.StringUtil;
 import com.intellij.psi.tree.IElementType;
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
 import org.jetbrains.jet.lang.descriptors.*;
 import org.jetbrains.jet.lang.descriptors.annotations.Annotated;
 import org.jetbrains.jet.lang.descriptors.annotations.AnnotationDescriptor;
@@ -180,15 +179,12 @@ public class DescriptorRendererImpl implements DescriptorRenderer {
     /* TYPES RENDERING */
     @NotNull
     @Override
-    public String renderType(@Nullable JetType type) {
+    public String renderType(@NotNull JetType type) {
         return escape(renderTypeWithoutEscape(type));
     }
 
-    private String renderTypeWithoutEscape(@Nullable JetType type) {
-        if (type == null) {
-            return "[NULL]";
-        }
-        else if (type == CallResolverUtil.DONT_CARE || type == CallResolverUtil.CANT_INFER) {
+    private String renderTypeWithoutEscape(@NotNull JetType type) {
+        if (type == CallResolverUtil.DONT_CARE || type == CallResolverUtil.CANT_INFER) {
             return "???";
         }
         else if (type == CallResolverUtil.PLACEHOLDER_FUNCTION_TYPE) {
@@ -432,7 +428,8 @@ public class DescriptorRendererImpl implements DescriptorRenderer {
 
         renderName(function, builder);
         renderValueParameters(function, builder);
-        builder.append(" : ").append(escape(renderType(function.getReturnType())));
+        JetType returnType = function.getReturnType();
+        builder.append(" : ").append(returnType == null ? "[NULL]" : escape(renderType(returnType)));
         renderWhereSuffix(function.getTypeParameters(), builder);
     }
 

compiler/tests/org/jetbrains/jet/types/TypeSubstitutorTest.java

@@ -53,7 +53,6 @@ import java.util.Map;
 
 @SuppressWarnings("unchecked")
 public class TypeSubstitutorTest extends KotlinTestWithEnvironment {
-    public static final String ILLEGAL_SUBSTITUTION = "[NULL]";
     private JetScope scope;
     private InjectorForTests injector;
 
@@ -106,7 +105,13 @@ public class TypeSubstitutorTest extends KotlinTestWithEnvironment {
 
         JetType result = substitutor.substitute(initialType, Variance.INVARIANT);
 
-        assertEquals(expectedTypeStr, DescriptorRenderer.SHORT_NAMES_IN_TYPES.renderType(result));
+        if (expectedTypeStr == null) {
+            assertNull(result);
+        }
+        else {
+            assertNotNull(result);
+            assertEquals(expectedTypeStr, DescriptorRenderer.SHORT_NAMES_IN_TYPES.renderType(result));
+        }
     }
 
     private Map<TypeConstructor, TypeProjection> stringsToSubstitutionMap(Pair<String, String>[] substitutionStrs) {
@@ -218,7 +223,7 @@ public class TypeSubstitutorTest extends KotlinTestWithEnvironment {
 
     public void testInOutProjection() throws Exception {
         doTest(
-                ILLEGAL_SUBSTITUTION,
+                null,
                 "C<in T>",
                 map("T", "out String")
         );

idea/src/org/jetbrains/jet/plugin/highlighter/IdeErrorMessages.java

@@ -20,6 +20,7 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.jet.lang.descriptors.CallableMemberDescriptor;
 import org.jetbrains.jet.lang.diagnostics.Diagnostic;
 import org.jetbrains.jet.lang.diagnostics.rendering.*;
+import org.jetbrains.jet.lang.types.JetType;
 import org.jetbrains.jet.renderer.DescriptorRenderer;
 
 import static org.jetbrains.jet.lang.diagnostics.Errors.*;
@@ -86,7 +87,9 @@ public class IdeErrorMessages {
                     @NotNull
                     @Override
                     public String render(@NotNull CallableMemberDescriptor object) {
-                        return DescriptorRenderer.HTML.renderType(object.getReturnType());
+                        JetType returnType = object.getReturnType();
+                        assert returnType != null;
+                        return DescriptorRenderer.HTML.renderType(returnType);
                     }
                 }, DescriptorRenderer.HTML);
 

idea/src/org/jetbrains/jet/plugin/structureView/JetStructureViewElement.java

@@ -215,6 +215,7 @@ public class JetStructureViewElement implements StructureViewTreeElement {
             textBuilder.append("(").append(parametersString).append(")");
 
             JetType returnType = functionDescriptor.getReturnType();
+            assert returnType != null;
             textBuilder.append(":").append(DescriptorRenderer.TEXT.renderType(returnType));
         }
         else if (descriptor instanceof VariableDescriptor) {