Disallow Arg wrapped Args and exceptions

[SerialVelocity]

What happened?

Arg<?> someSharedArg = UnsafeArg.of("arg", arg);
log.error("ERROR", SafeArg.of("arg", someSharedArg));

This will have output similar to:

{"key":"arg","value":["arg-val"],"safeForLogging":false}

The same happens with exceptions (if the exception is "safe"):

log.error("ERROR", SafeArg.of("exception", e));

What did you want to happen?

Error-prone should complain that these are invalid.

[iamdanfox]

@SerialVelocity would you be able to put up a quick PR for this? I think it could look quite similar to https://github.com/palantir/gradle-baseline/blob/develop/baseline-error-prone/src/main/java/com/palantir/baseline/errorprone/DangerousThrowableMessageSafeArg.java

[stale[bot]]

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