grep: fix --follow with no --diff nor --rev to not fall back to plain grep Before, "grep --follow" would only print matches in the working directory. Since --follow is the option to specify the search space, it should disable the plain (i.e. wdir) grep.

test-grep: add tests for --follow with/without --diff and/or paths This tests the behavior of cmdutil.walkchangerevs(). I'm going to rewrite cmdutil.walkchangerevs() to leverage the "log -f" logic, but the code coverage looked quite small. And the history traversal of "grep -f" goes wrong in various ways.

grep: clarify that --all works exactly the same way as --diff 7fbb5d76c555 "grep: add --diff flag" says as such, but the help strings have diverged since, and it's getting fuzzier what this --all will do.

churn: add an usage example in docstring

tests: run test-check-py3-compat only in pure python mode This test was added few years ago to detect syntax and import related warnings and kickstart the python-3 porting efforts. It tries to parse the ast and import the module. When using in strict modes like `HGMODULEPOLICY=rust` or `HGMODULEPOLICY=c`, the test fails. Let's run the test only on pure python mode. We now have full test suite being run with python 3 and some people even use hg with python 3 in production (like me).

log: make -frREV PATH detect missing files before falling back to slow path If -rREV isn't specified, "log --follow" would abort on nonexistent paths. Let's implement this behavior for "-frREV" case as we have ctx.hasdir() now. Otherwise "log -frREV PATH" would silently fall back to slow path and files wouldn't be followed across renames. The loop is quadratic (as before), but the size of the startctxs and match.files() should be small in general. Some tests are marked as BROKEN since file renames aren't tracked in the slow path. This is a known limitation of the current history traversal function.

log: fix -fr'wdir()' PATH to follow newly added file Testing filelog doesn't make sense in this case because the file existence is tested against the specified changectxs. If the filelog is empty and if startctxs != [wctx], 'f not in c' should be triggered.