RFR: 8257872: UL: -Xlog does not check number of options

[Ioi Lam]

On Tue, 8 Dec 2020 03:02:03 GMT, Koichi Sakata <ksakata at openjdk.org> wrote:

> In Unified Logging options can be specified up to four (`-Xlog[:[selections][:[output][:[decorators][:output-options]]]]`).
> But it’s possible to specify options with more colons like `java -Xlog:::::`.
> It’s better to show a message when more options are specified than maximum number.
> 
> By this PR a warning message is outputted when options are specified more than the max number.

Should this be a warning or an error? The behavior seems inconsistent:

$ java -Xlog:gc=error:::foo -version
[0.000s][warning][logging] Output options for existing outputs are ignored.
java version "16-internal" 2021-03-16
Java(TM) SE Runtime Environment (build 16-internal+0-adhoc.iklam.open)
Java HotSpot(TM) 64-Bit Server VM (build 16-internal+0-adhoc.iklam.open, mixed mode, sharing)

$ java -Xlog:gc=error::foo -version
[0.000s][error][logging] Invalid decorator 'foo'.
Invalid -Xlog option '-Xlog:gc=error::foo', see error log for details.
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

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PR: https://git.openjdk.java.net/jdk/pull/1685