Re: [PATCH 6/7] test-lib: make --verbose output valid TAP

Make the --verbose output be valid TAP, making it machine-readable for
TAP parsers again.

Both the verbose and non-verbose test outputs were valid TAP back when
I added support for TAP in 5099b99d25f (test-lib: Adjust output to be
valid TAP format, 2010-06-24).

Sometime after that the --verbose output broke due to some tests
emitting their own lines starting "ok" (or otherwise invalidate the
TAP). That was noticed and fixed in 452320f1f5 (test-lib: add
--verbose-log option, 2016-10-21) and "fixed" by simply turning off
the verbose mode when we were running under TAP::Harness (e.g. under
"prove").

That solution worked for running under Travis CI. After that fix it
was made to use the --verbose-log option in 041c72de109 (travis: use
--verbose-log test option, 2016-10-21), see 522354d70f4 (Add Travis CI
support, 2015-11-27) for the "cat t/test-results/*.out" code that was
aimed at.

But that solution and others discussed in 452320f1f5 closed the door
on us having reliable machine-readable TAP output.

Let's instead revert the work done in 452320f1f5 and, as well as the
follow-up commits 88c6e9d31c (test-lib: --valgrind should not override
--verbose-log, 2017-09-05) and f5ba2de6bc (test-lib: make "-x" work
with "--verbose-log", 2017-12-08), which were only needed to work
around bugs in the the previous --verbose-log implementation.

Replace it with a simple method for ensuring that we have valid TAP
both on stdout, and in any verbose output we write. When we detect
that we're running under "prove" we prefix all legitimate TAP
directives with "GIT_TEST_TEE_STARTED":

    $ GIT_TEST_TEE_STARTED=1 ./t5547-push-quarantine.sh
    GIT_TEST_TEE_STARTED ok 1 - create picky dest repo
    GIT_TEST_TEE_STARTED ok 2 - accepted objects work
    [...]
    GIT_TEST_TEE_STARTED 1..6

Then, instead of piping the output to "tee -a" we pipe it to a helper
which first converts "ok" and other TAP syntax to e.g. "\ok", and then
strips that "GIT_TEST_TEE_STARTED " prefix from the start of the line.

The end result is that we're guaranteed to have valid TAP syntax on
stdout.

We can thus get rid of the --verbose-log special-case. Since that
option was meant to get around the TAP issue let's simply make it an
alias for "--verbose --tee".

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 t/README         |  9 ++++++---
 t/t0000-basic.sh |  8 ++++++++
 t/test-lib.sh    | 43 +++++++++++++++++++++----------------------
 3 files changed, 35 insertions(+), 25 deletions(-)

diff --git a/t/README b/t/README
index 2cc8cbc7185..f09d94e754e 100644
--- a/t/README
+++ b/t/README

@@ -157,10 +157,13 @@ appropriately before running "make". Short options can be bundled, i.e.
 
 -V::
 --verbose-log::
-	Write verbose output to the same logfile as `--tee`, but do
-	_not_ write it to stdout. Unlike `--tee --verbose`, this option
+	An alias for `--verbose --tee`. This option
 	is safe to use when stdout is being consumed by a TAP parser
-	like `prove`. Implies `--tee` and `--verbose`.
+	like `prove`.
+	Historically this option was different from `--verbose --tee`
+	and would not write any verbose output to stdout to ensure the
+	TAP-correctness of the output. The TAP-correctness of the
+	output is now sanity checked by the test library,