tests: start asserting that *.txt SYNOPSIS matches -h output

There's been a lot of incremental effort to make the SYNOPSIS output
in our documentation consistent with the -h output,
e.g. cbe485298b (git reflog [expire|delete]: make -h output
consistent with SYNOPSIS, 2022-03-17) is one recent example, but that
effort has been an uphill battle due to the lack of regression
testing.

This adds such regression testing, we can parse out the SYNOPSIS
output with "sed", and it turns out it's relatively easy to normalize
it and the "-h" output to match on another.

We now ensure that we won't have regressions when it comes to the list
of commands in "expect_help_to_match_txt" below, and in subsequent
commits we'll make more of them consistent.

The naïve parser here gets quite a few things wrong, but it doesn't
need to be perfect, just good enough that we can compare /some/ of
this help output. There's no cases where the output would match except
for the parser's stupidity, it's all cases of e.g. comparing the *.txt
to non-parse_options() output.

Since that output is wildly different than the *.txt anyway let's
leave this for now, we can fix the parser some other time, or it won't
become necessary as we'll e.g. convert more things to using
parse_options().

Having a special-case for "merge-tree"'s 1f0c3a29da (merge-tree:
implement real merges, 2022-06-18) is a bit ugly, but preferred to
blessing that " (deprecated)" pattern for other commands. We'd
probably want to add some other way of marking deprecated commands in
the SYNOPSIS syntax. Syntactically 1f0c3a29da3's way of doing it is
indistinguishable from the command taking an optional literal
"deprecated" string as an argument.

Some of the issues that are left:

 * "git show -h", "git whatchanged -h" and "git reflog --oneline -h"
   all showing "git log" and "git show" usage output. I.e. the
   "builtin_log_usage" in builtin/log.c doesn't take into account what
   command we're running.

 * Commands which implement subcommands such as like
   "multi-pack-index", "notes", "remote" etc. having their subcommands
   in a very different order in the *.txt and *.c. Fixing it would
   require some verbose diffs, so it's been left alone for now.

 * Commands such as "format-patch" have a very long argument list in
   the *.txt, but just "[<options>]" in the *.c.

   What to do about these has been left out of this series, except to
   the extent that preceding commits changed "[<options>]" (or
   equivalent) to the list of options in cases where that list of
   options was tiny, or we clearly meant to exhaustively list the
   options in both *.txt and *.c.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t0450-txt-doc-vs-help.sh

@@ -1,6 +1,9 @@
 #!/bin/sh
 
-test_description='assert (unbuilt) Documentation/*.txt and -h output'
+test_description='assert (unbuilt) Documentation/*.txt and -h output
+
+Run this with --debug to see a summary of where we still fail to make
+the two versions consistent with one another.'
 
 TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
@@ -9,6 +12,14 @@ test_expect_success 'setup: list of builtins' '
 	git --list-cmds=builtins >builtins
 '
 
+test_expect_success 'list of txt and help mismatches is sorted' '
+	sort -u "$TEST_DIRECTORY"/t0450/txt-help-mismatches >expect &&
+	if ! test_cmp expect "$TEST_DIRECTORY"/t0450/txt-help-mismatches
+	then
+		BUG "please keep the list of txt and help mismatches sorted"
+	fi
+'
+
 help_to_synopsis () {
 	builtin="$1" &&
 	out_dir="out/$builtin" &&
@@ -49,6 +60,9 @@ txt_to_synopsis () {
 			/^$/d;
 			/^\[verse\]$/d;
 
+			s/{litdd}/--/g;
+			s/'\''\(git[ a-z-]*\)'\''/\1/g;
+
 			p;
 		}' \
 		<"$b2t" >"$out" &&
@@ -61,6 +75,15 @@ check_dashed_labels () {
 
 HT="	"
 
+align_after_nl () {
+	builtin="$1" &&
+	len=$(printf "git %s " "$builtin" | wc -c) &&
+	pad=$(printf "%${len}s" "") &&
+
+	sed "s/^[ $HT][ $HT]*/$pad/"
+}
+
+test_debug '>failing'
 while read builtin
 do
 	# -h output assertions
@@ -85,6 +108,50 @@ do
 	test_expect_success "$preq" "$builtin *.txt SYNOPSIS has dashed labels" '
 		check_dashed_labels "$(txt_to_synopsis "$builtin")"
 	'
+
+	# *.txt output consistency assertions
+	result=
+	if grep -q "^$builtin$" "$TEST_DIRECTORY"/t0450/txt-help-mismatches
+	then
+		result=failure
+	else
+		result=success
+	fi &&
+	test_expect_$result "$preq" "$builtin -h output and SYNOPSIS agree" '
+		t2s="$(txt_to_synopsis "$builtin")" &&
+		if test "$builtin" = "merge-tree"
+		then
+			test_when_finished "rm -f t2s.new" &&
+			sed -e '\''s/ (deprecated)$//g'\'' <"$t2s" >t2s.new
+			t2s=t2s.new
+		fi &&
+		h2s="$(help_to_synopsis "$builtin")" &&
+
+		# The *.txt and -h use different spacing for the
+		# alignment of continued usage output, normalize it.
+		align_after_nl "$builtin" <"$t2s" >txt &&
+		align_after_nl "$builtin" <"$h2s" >help &&
+		test_cmp txt help
+	'
+
+	if test_have_prereq "$preq" && test -e txt && test -e help
+	then
+		test_debug '
+			if test_cmp txt help >cmp 2>/dev/null
+			then
+				echo "=== DONE: $builtin ==="
+			else
+				echo "=== TODO: $builtin ===" &&
+				cat cmp
+			fi >>failing
+		'
+
+		# Not in test_expect_success in case --run is being
+		# used with --debug
+		rm -f txt help tmp 2>/dev/null
+	fi
 done <builtins
 
+test_debug 'say "$(cat failing)"'
+
 test_done

t/t0450/txt-help-mismatches

@@ -0,0 +1,58 @@
+add
+am
+apply
+archive
+bisect
+blame
+branch
+check-ref-format
+checkout
+checkout-index
+clone
+column
+config
+credential
+credential-cache
+credential-store
+fast-export
+fast-import
+fetch-pack
+fmt-merge-msg
+for-each-ref
+format-patch
+fsck-objects
+fsmonitor--daemon
+gc
+grep
+index-pack
+init-db
+log
+ls-files
+ls-tree
+mailinfo
+mailsplit
+maintenance
+merge
+merge-file
+merge-index
+merge-one-file
+multi-pack-index
+name-rev
+notes
+pack-objects
+push
+range-diff
+rebase
+remote
+remote-ext
+remote-fd
+repack
+reset
+restore
+rev-parse
+show
+stage
+switch
+update-index
+update-ref
+whatchanged