Proposal: Warnings for unnecessary warning suppression

[Archie Cobbs]

On Thu, Mar 6, 2025 at 9:45 AM Magnus Ihse Bursie <
magnus.ihse.bursie at oracle.com> wrote:

> But having warning suppression that does not make sense for a given
> compiler is not necessary a problem, and if it should be flagged, it
> should be something you opt into, and possibly, as Joe suggests, somehow
> lie outside normal warnings.


I did think about this question of interactions between -Werror, -Xlint:all,
and different compiler versions with respect to these new warning
categories. In particular, thinking through the scenarios is why the
-Xlint:suppression flag is ignored unless the -Xlint:options flag is also
enabled (see below).

Here are my thoughts... please check my logic:

   - In the case of @SuppressWarnings annotations:
      - What if a compiler doesn't recognize
      @SuppressWarnings("suppression")?
         - No problem - it's already the case that unrecognized keys are
         ignored
      - What if two compiler versions handle some warning "foo"
      differently, so that one warns where one doesn't?
         - In this case @SuppressWarnings("foo") will be unnecessary in one
         case but not the other
            - In the latter you'd then get a "suppression" warning if
            enabled and the compiler supports it
         - But this happens all the time - i.e., a new warning is
         introduced or an existing warning's behavior changes
         - The usual answer is to add @SuppressWarnings("foo") to suppress
         the warning in the compiler version where it occurs
         - Similarly, the answer here is to add
         @SuppressWarnings("suppression") to suppress the warning in the
         compiler version where it occurs
      - In the case of -Xlint:suppression-option flags:
      - It's always safe to add -Xlint:-suppression-option to a build to
      restore the current behavior IF every compiler version knows that flag
      - If some compiler version doesn't know -Xlint:-suppression-option
      then -Xlint:-options also works
      - So there's always a way to disable suppression warnings, regardless
      of whether the compiler knows about "suppression-option"
      - Using -Xlint:-options  is only a temporary measure until all
      compiler versions support "suppression-option

-Archie

-- 
Archie L. Cobbs
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