Enhanced warning suppression

[stephan-herrmann]

Via https://bugs.openjdk.org/browse/JDK-8356043 javac starts to report when @SuppressWarnings is unnecesary (which ecj does since 2008).

There are, however, a few interesting bits in this, which are worth considering for ecj:

• make the warning about unnecessary SW suppressable by saying @SuppressWarnings("suppression")
• if we want to further align warnings between javac and ecj we may refer to the following file to learn about details of warning categories: https://github.com/openjdk/jdk/blob/master/src/jdk.compiler/share/classes/com/sun/tools/javac/resources/compiler.properties
  • for a list of javac warning categories I was pointed to https://docs.oracle.com/en/java/javase/25/docs/specs/man/javac.html#option-Xlint-custom
  • alternatively, javac --help-lint should print the same
  • would it be useful to add this list to ecj, so that instead of reporting Unsupported @SuppressWarnings("this-escape") we could just remain silent? If a token is in the list of javac's categories, it's less likely to be a simple typo.
• in discussion I was reminded that the following clumsy message could perhaps be avoided: "At least one of the problems in category 'foo' is not analysed due to a compiler option being ignored":
  • if "supression" warnings are enabled, this might tell the compiler to perform even disabled analyses. We should discuss if "technically" enabling all analyses and filtering only during ProblemHandler.handle() is acceptable in that case.
    • previous discussion in this regard happened here: https://bugs.eclipse.org/bugs/show_bug.cgi?id=506888#c12 (with negative result)
  • for a recent issue see Confusing "At least one of the problems in category 'resource' is not analysed due to a compiler option being ignored" #2279
  • OTOH, it might suffice to implement @SuppressWarnings("suppression") and where the undesired info appears, just add "suppression".

[stephan-herrmann]

https://bugs.eclipse.org/bugs/show_bug.cgi?id=506888#c18 discussed an implementation strategy whereby problems can be recorded at all levels: error, warning, info and even ignore. Then a Problem at level ignore could still be used to match against SW, but it will never create any marker :)