DetailASTTest: 'checkTree' failing on deep AST tree

[rnveach]

Taken from #3894 (comment) and seen at https://travis-ci.org/checkstyle/checkstyle/jobs/208912195#L254 ,

java.lang.StackOverflowError
at com.puppycrawl.tools.checkstyle.api.DetailASTTest.checkTree(DetailASTTest.java:158)

We should find a way to re-write this test, if possible, so it doesn't use the stack for each child.
When we run this on a deeply nested tree, we get a stackoverflow.
We should be able to walk through the tree like we do in other areas, see

checkstyle/src/main/java/com/puppycrawl/tools/checkstyle/TreeWalker.java

Lines 495 to 508 in b4a337a

	private void processIter(DetailAST root, AstState astState) {
	DetailAST curNode = root;
	while (curNode != null) {
	notifyVisit(curNode, astState);
	DetailAST toVisit = curNode.getFirstChild();
	while (curNode != null && toVisit == null) {
	notifyLeave(curNode, astState);
	toVisit = curNode.getNextSibling();
	if (toVisit == null) {
	curNode = curNode.getParent();
	}
	}
	curNode = toVisit;
	}

Any file skips in this test should be removed as proof the fix works.

[Luolc]

I have reviewed some codes in DetailASTTest when handling #3700. I think I am able to rewrite the test 😄
I will work on it once approved.

[romani]

Approved

[rnveach]

@Luolc Since your PR fixed the file with the original test, it is probably best to start off with another file that will fail and then provide fix to show it isn't an issue anymore.

[Luolc]

@rnveach That makes sense. So the steps tend to be:

1. Create an input file and let the CI fail.
2. Rewrite the test to prove the fix will work on a deeply nested tree.
3. Delete the input file.
   I will do that step by step 😄

[rnveach]

So the steps tend to be
3. Delete the input file.

Yes to all except step 3. The file needs to stay to prove we don't revert back and break the test again.
CI is our mini-regression. We want to keep moving forward and not have to redo fixes again and again.

[Luolc]

@rnveach Got it. Just not sure where to put the input file. I am doing with step one now and the input file is put at https://github.com/checkstyle/checkstyle/tree/master/src/test/resources/com/puppycrawl/tools/checkstyle/checks (where the InputAllEscapedUnicodeCharacters in #3700 is). Should I put the file at https://github.com/checkstyle/checkstyle/tree/master/src/test/resources/com/puppycrawl/tools/checkstyle/api? (same package as DetailASTTest)

[rnveach]

@Luolc Since its an input file to the test, it should be in the same package as the test.

[Luolc]

@rnveach Done. Shall we move the discussion to the PR page #3966 ? 😄

[romani]

fix is merged.