A variable declared to suppress a warning throws the same warning on second assignment.

[Utkarsh Rai]

Minimum Working Example -

import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

public class BugCheck {
public static void main(String[] args) {
@SuppressWarnings("assignment.type.incompatible")
@NonNull String s1 = nString1();
s1 = nString2();
}

private static @Nullable String nString2() {
return "World";
}

private static @Nullable String nString1() {
return "Hello";
}
}

Command -

javacheck -processor nullness BugCheck.java

Expected behavior -

Compile normally.

Actual behavior -

BugCheck.java:8: error: [assignment.type.incompatible] incompatible types in assignment.
        s1 = nString2();
                     ^
  found: @Initialized @Nullable String
  required: @UnknownInitialization @NonNull String
1 error

Comments -

This might be the expected behavior to prevent the misuse of variable s1 further in the code, but I read through section 29.1 (@SuppressWarnings annotation) in the manual and did not find any clarifications regarding this, so I decided to report it. This is a recurring pattern in my case study where I have to transfer the (Nullable) contents of a ResultSet to an ArrayList which holds NonNull elements, where I can guarantee that the contents are not null.

Thanks in advance.

[Michael Ernst]

This is the documented behavior of the @SuppressWarnings annotation.  That warning is defined by Java, so this isn't specific to the Checker Framework.  A @SuppressWarnings annotation applies to all warnings within the program element on which it is written.  The Checker Framework Manual explains this, in the 4th sentence of the section you cited:  "It [a @SuppressWarnings annotation] suppresses all warnings within that program element."  The program element is the declaration, not all uses of the variable.

Mike

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[Utkarsh Rai]

"The program element is the declaration, not all uses of the variable.", this is what I was missing.

Thanks for the clarification.

[Michael Ernst]

I also added a clarification to the manual:

https://github.com/typetools/checker-framework/commit/57dd3519ba47343d4cf9928d1b415d9e59a19329

To view this discussion on the web visit https://groups.google.com/d/msgid/checker-framework-gsoc/01097b85-51a7-49f6-8954-3eb497730306n%40googlegroups.com.