Add support for custom ktlint reporters

[Tapchicoma]

Closes #125

[JLLeitschuh]

Can you put a README in samples/kotlin-reporter-creating describing the structure? Would it help?

Do we need to explain to developers that if they side effect change other files outside of the input and output we won't see their changes and it won't get captured in Gradle's "out of date" checking.

Also, just checking, how do custom reporters work with the Gradle Build Cache?

[Tapchicoma]

Can you put a README in samples/kotlin-reporter-creating describing the structure? Would it help?

Maybe I misunderstand you, but why we need to add README how to create ktlint reporter? It should be in a ktlint project.

Do we need to explain to developers that if they side effect change other files outside of the input and output we won't see their changes and it won't get captured in Gradle's "out of date" checking.

Can you explain here?

Also, just checking, how do custom reporters work with the Gradle Build Cache?

Should work, as all reporters produces task @OutputFiles property. I will add additional tests for it.

[JLLeitschuh]

Do we need to explain to developers that if they side effect change other files outside of the input and output we won't see their changes and it won't get captured in Gradle's "out of date" checking.

Can you explain here?

For example:

If you side effect other files in your report, you will need to manually add those side affected files as outputs of the Gradle task. Failure to do so will mean that Gradle will be unable to fully detect all file changed by the task and thus may incorrectly mark your tasks as "up-to-date" when they actually aren't.

[Tapchicoma]

If you side effect other files in your report, you will need to manually add those side affected files as outputs of the Gradle task. Failure to do so will mean that Gradle will be unable to fully detect all file changed by the task and thus may incorrectly mark your tasks as "up-to-date" when they actually aren't.

Sorry, still don't get it fully - how can consume "side-effect" output file?

All 3rd party output reports are added to task outputs, so if they will be removed or modified - task will re-run again.

[JLLeitschuh]

Example:

class CsvReporter(
    private val out: PrintStream
) : Reporter {
    override fun onLintError(file: String, err: LintError, corrected: Boolean) {
        val line = "$file;${err.line};${err.col};${err.ruleId};${err.detail};$corrected"
        out.println(line)
        File("some_other_file.txt").write(line) // Side effect: `some_other_file.txt` won't be captued as an "output"
    }
}

[Tapchicoma]

Now I got it. Yeah, such "side effect" should be mentioned in README. Not sure if it should be in this project or ktlint? 🤔

[JLLeitschuh]

Yeah, such "side effect" should be mentioned in README. Not sure if it should be in this project or ktlint?

Not sure. Both?

[AdamMc331]

Is this still in development? I was looking into the idea of a custom reporter to tweak the colored output for KtLint, being discussed here: pinterest/ktlint#582

Am I unable to implement a custom reporter without this PR being merged?

[Tapchicoma]

Yes, I am planning to finish it before next release (pretty soon). Until then, unfortunately, you can't use custom reporter with this plugin.

[AdamMc331]

Thanks for the update! Ping me if I can provide assistance in any way. :)

[Tapchicoma]

@JLLeitschuh this PR is ready to be reviewed again

[JLLeitschuh]

LGTM!