chainlint.pl: check line numbers in expected output

chainlint.pl: check line numbers in expected output

While working on chainlint.pl recently, we introduced some bugs that
showed incorrect line numbers in the output. But it was hard to notice,
since we sanitize the output by removing all of the line numbers! It
would be nice to retain these so we can catch any regressions.

The main reason we sanitize is for maintainability: we concatenate all
of the test snippets into a single file, so it's hard for each ".expect"
file to know at which offset its test input will be found. We can handle
that by storing the per-test line numbers in the ".expect" files, and
then dynamically offsetting them as we build the concatenated test and
expect files together.

The changes to the ".expect" files look like tedious boilerplate, but it
actually makes adding new tests easier. You can now just run:

  perl chainlint.pl chainlint/foo.test |
  tail -n +2 >chainlint/foo.expect

to save the output of the script minus the comment headers (after
checking that it is correct, of course). Whereas before you had to strip
the line numbers. The conversions here were done mechanically using
something like the script above, and then spot-checked manually.

It would be possible to do all of this in shell via the Makefile, but it
gets a bit complicated (and requires a lot of extra processes). Instead,
I've written a short perl script that generates the concatenated files
(we already depend on perl, since chainlint.pl uses it). Incidentally,
this improves a few other things:

  - we incorrectly used $(CHAINLINTTMP_SQ) inside a double-quoted
    string. So if your test directory required quoting, like:

       make "TEST_OUTPUT_DIRECTORY=/tmp/h'orrible"

    we'd fail the chainlint tests.

  - the shell in the Makefile didn't handle &&-chaining correctly in its
    loops (though in practice the "sed" and "cat" invocations are not
    likely to fail).

  - likewise, the sed invocation to strip numbers was hiding the exit
    code of chainlint.pl itself. In practice this isn't a big deal;
    since there are linter violations in the test files, we expect it to
    exit non-zero. But we could later use exit codes to distinguish
    serious errors from expected ones.

  - we now use a constant number of processes, instead of scaling with
    the number of test scripts. So it should be a little faster (on my
    machine, "make check-chainlint" goes from 133ms to 73ms).

There are some alternatives to this approach, but I think this is still
a good intermediate step:

  1. We could invoke chainlint.pl individually on each test file, and
     compare it to the expected output (and possibly using "make" to
     avoid repeating already-done checks). This is a much bigger change
     (and we'd have to figure out what to do with the "# LINT" lines in
     the inputs). But in this case we'd still want the "expect" files to
     be annotated with line numbers. So most of what's in this patch
     would be needed anyway.

  2. Likewise, we could run a single chainlint.pl and feed it all of the
     scripts (with "--jobs=1" to get deterministic output). But we'd
     still need to annotate the scripts as we did here, and we'd still
     need to either assemble the "expect" file, or break apart the
     script output to compare to each individual ".expect" file.

So we may pursue those in the long run, but this patch gives us more
robust tests without too much extra work or moving in a useless
direction.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>