The javac compiler should include the string 'error' in any error messages.

Historically, javac emitted few warning messages, so any messages emitted were clearly errors, so these didn't have the word 'error' in them. More recently the JLS has started to require warning messages in certain cases, and javac has options that will cause additional warnings to be emitted. These warning messages all include the string 'warning' in the message text.

Ideally every code base should compile without any warnings, however, sadly, this isn't always the case. This gives rise to the possibility of a javac run emitting dozens or hundreds of warnings, with an error buried somewhere in the middle. The error message is distinguished by the *lack* of the word 'warning' in the message text. This makes it difficult to find the error in an IDE output window or in a build log file. It's certainly possible to capture the output and delete all the warnings and the corresponding source lines, leaving just the errors, but this is quite inconvenient.

It seems unlikely that adding 'error' to the text of error messages would be incompatible. If it is, however, it might be possible to mitigate the incompatibility through some option such as -XDdiags.