Add ratchetFrom to maven

[nedtwigg]

HELP WANTED. This unfinished PR implements ratchetFrom 'origin/master', which is currently only available in plugin-gradle. I am not a maven user, finishing this PR is not going to make the top of my todo list. However, I have outlined the work necessary to complete this PR, so that any interested party can take it to the finish line.

Basic implementation

In order to integrate it into maven, we need to take these two places in the maven plugin:

spotless/plugin-maven/src/main/java/com/diffplug/spotless/maven/SpotlessCheckMojo.java

Lines 52 to 55 in e374870

	PaddedCell.DirtyState dirtyState = PaddedCell.calculateDirtyState(formatter, file);
	if (!dirtyState.isClean() && !dirtyState.didNotConverge()) {
	problemFiles.add(file);
	}

spotless/plugin-maven/src/main/java/com/diffplug/spotless/maven/SpotlessApplyMojo.java

Lines 46 to 49 in e374870

	PaddedCell.DirtyState dirtyState = PaddedCell.calculateDirtyState(formatter, file);
	if (!dirtyState.isClean() && !dirtyState.didNotConverge()) {
	dirtyState.writeCanonicalTo(file);
	}

and make it look like this place in the gradle plugin (broader context in #590).

spotless/plugin-gradle/src/main/java/com/diffplug/gradle/spotless/SpotlessTask.java

Lines 125 to 130 in e374870

	PaddedCell.DirtyState dirtyState;
	if (ratchet != null && ratchet.isClean(getProject(), rootTreeSha, input)) {
	dirtyState = PaddedCell.isClean();
	} else {
	dirtyState = PaddedCell.calculateDirtyState(formatter, input);
	}

We'll also need a test, this one from gradle gets the job done pretty well:

spotless/plugin-gradle/src/test/java/com/diffplug/gradle/spotless/RatchetFromTest.java

Lines 37 to 108 in e374870

	@Test
	public void singleProjectExhaustive() throws Exception {
	try (Git git = Git.init().setDirectory(rootFolder()).call()) {
	setFile("build.gradle").toLines(
	"plugins { id 'com.diffplug.gradle.spotless' }",
	"spotless {",
	" ratchetFrom 'baseline'",
	" format 'misc', {",
	" target 'src/markdown/*.md'",
	" custom 'lowercase', { str -> str.toLowerCase() }",
	" bumpThisNumberIfACustomStepChanges(1)",
	" }",
	"}");
	setFile(TEST_PATH).toContent("HELLO");
	git.add().addFilepattern(TEST_PATH).call();
	git.commit().setMessage("Initial state").call();
	// tag this initial state as the baseline for spotless to ratchet from
	git.tag().setName("baseline").call();
	// so at this point we have test.md, and it would normally be dirty,
	// but because it is unchanged, spotless says it is clean
	assertClean();
	// but if we change it so that it is not clean, spotless will now say it is dirty
	setFile(TEST_PATH).toContent("HELLO WORLD");
	assertDirty();
	gradleRunner().withArguments("spotlessApply").build();
	assertFile(TEST_PATH).hasContent("hello world");
	// but if we make it unchanged again, it goes back to being clean
	setFile(TEST_PATH).toContent("HELLO");
	assertClean();
	// and if we make the index dirty
	setFile(TEST_PATH).toContent("HELLO WORLD");
	git.add().addFilepattern(TEST_PATH).call();
	{
	// and the content dirty in the same way, then it's dirty
	assertDirty();
	// if we make the content something else dirty, then it's dirty
	setFile(TEST_PATH).toContent("HELLO MOM");
	assertDirty();
	// if we make the content unchanged, even though index it and index are dirty, then it's clean
	setFile(TEST_PATH).toContent("HELLO");
	assertClean();
	// if we delete the file, but it's still in the index, then it's clean
	setFile(TEST_PATH).deleted();
	assertClean();
	}
	// if we remove the file from the index
	git.rm().addFilepattern(TEST_PATH).setCached(true).call();
	{
	// and it's gone in real life too, then it's clean
	assertClean();
	// if the content is there and unchanged, then it's clean
	setFile(TEST_PATH).toContent("HELLO");
	assertClean();
	// if the content is dirty, then it's dirty
	setFile(TEST_PATH).toContent("HELLO WORLD");
	assertDirty();
	}
	// new files always get checked
	setFile("new.md").toContent("HELLO");
	{
	assertDirty();
	// even if they are added
	git.add().addFilepattern("new.md").call();
	assertDirty();
	}
	}
	}

Integration with license

Once that is done, there's a mildly tricky bit where you really want the license step's behavior to depend on whether ratchetFrom is enabled. Here is how it is documented in gradle, and here is how it is implemented:

spotless/plugin-gradle/src/main/java/com/diffplug/gradle/spotless/FormatExtension.java

Lines 464 to 468 in e374870

	return FormatterStep.createLazy(LicenseHeaderStep.name(), () -> {
	// by default, we should update the year if the user is using ratchetFrom
	boolean updateYear = updateYearWithLatest == null ? FormatExtension.this.spotless.getRatchetFrom() != null : updateYearWithLatest;
	return new LicenseHeaderStep(licenseHeader(), delimiter, yearSeparator, updateYear);
	}, step -> step::format);

[nedtwigg]

Will need to incorporate these commits

• 58931b3
• 56fcaa5

[nedtwigg]

I'm working on this now.