relax "!null" contract checking to accept exceptions thrown (IDEA-133488)

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/ContractChecker.java

@@ -97,7 +97,7 @@ class ContractChecker extends DataFlowRunner {
     }
 
     if (instruction instanceof ReturnInstruction) {
-      if (((ReturnInstruction)instruction).isViaException()) {
+      if (((ReturnInstruction)instruction).isViaException() && myContract.returnValue != MethodContract.ValueConstraint.NOT_NULL_VALUE) {
         ContainerUtil.addIfNotNull(myFailures, ((ReturnInstruction)instruction).getAnchor());
       }
     }

java/java-tests/testData/inspection/dataFlow/contractCheck/ExceptionWhenDeclaredNotNull.java

@@ -0,0 +1,17 @@
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+class Foo {
+
+  @Contract(value = "_, true -> !null")
+  public @Nullable String noNotAllowed(@NotNull String bar, boolean reallyNotAllowed) {
+    if (bar.equals("no")) {
+      if (reallyNotAllowed) {
+        throw new IllegalArgumentException("heck no");
+      }
+      return null;
+    }
+    return bar;
+  }
+}

java/java-tests/testData/inspection/dataFlow/contractCheck/FailDelegation.java

@@ -5,7 +5,7 @@ import org.jetbrains.annotations.Nullable;
 class Foo {
   @Contract("!null,true->!null")
   String delegationToInstance(@NotNull Foo f, boolean createIfNeeded) {
-    return <warning descr="Contract clause '!null, true -> !null' is violated: exception might be thrown instead of returning !null">f.getString(createIfNeeded)</warning>;
+    return f.getString(createIfNeeded); // not smart enough to check this 
   }
 
   @Contract("true->fail")

java/java-tests/testSrc/com/intellij/codeInspection/ContractCheckTest.java

@@ -36,6 +36,7 @@ public class ContractCheckTest extends LightCodeInsightFixtureTestCase {
   public void testDelegationWithUnknownArgument() { doTest(); }
   public void testEqualsUnknownValue() { doTest(); }
   public void testMissingFail() { doTest(); }
+  public void testExceptionWhenDeclaredNotNull() { doTest(); }
   public void testCheckSuperContract() { doTest(); }
   public void testNestedCallsMayThrow() { doTest(); }