completion: infer Throwable for thrown bounds in completion so more candidates would be applicable (IDEA-162710)

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

@@ -48,6 +48,11 @@ public class CompletionParameterTypeInferencePolicy extends ProcessCandidatePara
     }
   }
 
+  @Override
+  public boolean inferRuntimeExceptionForThrownBoundWithNoConstraints() {
+    return false;
+  }
+
   @Override
   public PsiType adjustInferredType(PsiManager manager, PsiType guess, ConstraintType constraintType) {
     if (guess != null && !(guess instanceof PsiWildcardType)) {

java/java-psi-api/src/com/intellij/psi/impl/source/resolve/ParameterTypeInferencePolicy.java

@@ -33,6 +33,10 @@ public abstract class ParameterTypeInferencePolicy {
 
   public abstract Pair<PsiType, ConstraintType> getInferredTypeWithNoConstraint(PsiManager manager, PsiType superType);
 
+  public boolean inferRuntimeExceptionForThrownBoundWithNoConstraints() {
+    return true;
+  }
+
   public abstract PsiType adjustInferredType(PsiManager manager, PsiType guess, ConstraintType second);
 
   public boolean isVarargsIgnored() {

java/java-psi-impl/src/com/intellij/psi/impl/source/resolve/graphInference/InferenceSession.java

@@ -1259,7 +1259,7 @@ public class InferenceSession {
     }
 
     if (type == PsiType.NULL) {
-      if (var.isThrownBound() && isThrowable(var.getBounds(InferenceBound.UPPER))) {
+      if (var.isThrownBound() && myPolicy.inferRuntimeExceptionForThrownBoundWithNoConstraints() && isThrowable(var.getBounds(InferenceBound.UPPER))) {
         type =  PsiType.getJavaLangRuntimeException(myManager, GlobalSearchScope.allScope(myManager.getProject()));
       }
       else {

java/java-tests/testData/codeInsight/completion/smartType/InferThrowableBoundInCompletion-out.java

@@ -0,0 +1,15 @@
+import java.io.IOException;
+import java.util.function.Function;
+
+class LocalDateTime {}
+class Launcher {
+  public static final Function<LocalDateTime, IOException> TO_STRING = (message) -> new IOException(message.toString());
+
+  public static void main(String[] args) throws Throwable{
+    throwException(new LocalDateTime(), TO_STRING);
+  }
+
+  public static <Ex extends Throwable> void throwException(LocalDateTime str, Function<LocalDateTime, Ex> exceptionBuilder) throws Ex {
+    throw exceptionBuilder.apply(str);
+  }
+}

java/java-tests/testData/codeInsight/completion/smartType/InferThrowableBoundInCompletion.java

@@ -0,0 +1,15 @@
+import java.io.IOException;
+import java.util.function.Function;
+
+class LocalDateTime {}
+class Launcher {
+  public static final Function<LocalDateTime, IOException> TO_STRING = (message) -> new IOException(message.toString());
+
+  public static void main(String[] args) throws Throwable{
+    throwException(new LocalDateTime(), TO<caret>);
+  }
+
+  public static <Ex extends Throwable> void throwException(LocalDateTime str, Function<LocalDateTime, Ex> exceptionBuilder) throws Ex {
+    throw exceptionBuilder.apply(str);
+  }
+}

java/java-tests/testSrc/com/intellij/codeInsight/completion/SmartType18CompletionTest.java

@@ -177,6 +177,12 @@ public void testConvertToObjectStream() {
     checkResultByFile("/" + getTestName(false) + "-out.java");
   }
 
+  public void testInferThrowableBoundInCompletion() {
+    configureByTestName();
+    myFixture.complete(CompletionType.SMART, 1);
+    checkResultByFile("/" + getTestName(false) + "-out.java");
+  }
+
   public void testInsideNewExpressionWithDiamondAndOverloadConstructors() throws Exception {
     configureByTestName();
     myFixture.complete(CompletionType.SMART, 1);