lambda: check all return expressions for constraints

java/java-psi-impl/src/com/intellij/psi/impl/source/resolve/PsiResolveHelperImpl.java

@@ -595,6 +595,7 @@ public class PsiResolveHelperImpl implements PsiResolveHelper {
       final PsiSubstitutor subst = resolveResult.getSubstitutor();
       final PsiType returnType = subst.substitute(method.getReturnType());
       if (returnType != null && returnType != PsiType.VOID) {
+        Pair<PsiType, ConstraintType> constraint = null;
         final List<PsiExpression> expressions = lambdaExpression.getReturnExpressions();
         for (final PsiExpression expression : expressions) {
           final boolean independent = LambdaUtil.isFreeFromTypeInferenceArgs(methodParameters, lambdaExpression, expression);
@@ -621,12 +622,20 @@ public class PsiResolveHelperImpl implements PsiResolveHelper {
           if (exprType == null){
             return FAILED_INFERENCE;
           }
-          Pair<PsiType, ConstraintType> constraint =
+
+          final Pair<PsiType, ConstraintType> returnExprConstraint =
             getSubstitutionForTypeParameterConstraint(typeParam, returnType, exprType, false, PsiUtil.getLanguageLevel(method));
-          if (constraint != null) {
-            return constraint; //todo check that all return statements lead to the same inference
+          if (returnExprConstraint != null) {
+            if (returnExprConstraint == FAILED_INFERENCE) return returnExprConstraint;
+            if (constraint != null) {
+              final PsiType leastUpperBound = GenericsUtil.getLeastUpperBound(constraint.getFirst(), returnExprConstraint.getFirst(), typeParam.getManager());
+              constraint = new Pair<PsiType, ConstraintType>(leastUpperBound, ConstraintType.SUPERTYPE);
+            } else {
+              constraint = returnExprConstraint;
+            }
           }
         }
+        if (constraint != null) return constraint;
       }
       for (PsiParameter parameter : methodParameters) {
         if (LambdaUtil.dependsOnTypeParams(parameter.getType(), lambdaExpression)) {

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/highlighting/TypeArgsConsistencyMisc1.java

@@ -1,3 +1,18 @@
+/*
+ * Copyright 2000-2012 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 import java.util.List;
 class Test1 {
     
@@ -23,6 +38,16 @@ class Test1 {
         bar2("", x -> x);
 
         bar3(x -> x, "");
+
+        int ixc = 42;
+        bar(x -> {
+              if (ixc == 2) return "aaa";
+              return x;
+           });
+        bar(x -> {
+              if (ixc == 2) return x;
+              return x;
+           });
     }
 }