doc SYNOPSIS & -h: use "-" to separate words in labels, not "_"

Change "builtin/credential-cache--daemon.c" to use "<socket-path>" not
"<socket_path>" in a placeholder label, almost all of our
documentation uses this form.

This is now consistent with the "If a placeholder has multiple words,
they are separated by dashes" guideline added in
9c9b4f2f8b (standardize usage info string format, 2015-01-13), let's
add a now-passing test to assert that that's the case.

To do this we need to introduce a very sed-powered parser to extract
the SYNOPSIS from the *.txt, and handle not all commands with "-h"
having a corresponding *.txt (e.g. "bisect--helper"). We'll still want
to handle syntax edge cases in the *.txt in subsequent commits for
other checks, but let's do that then.

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

builtin/credential-cache--daemon.c

@@ -267,7 +267,7 @@ int cmd_credential_cache_daemon(int argc, const char **argv, const char *prefix)
 	const char *socket_path;
 	int ignore_sighup = 0;
 	static const char *usage[] = {
-		"git-credential-cache--daemon [opts] <socket_path>",
+		"git-credential-cache--daemon [opts] <socket-path>",
 		NULL
 	};
 	int debug = 0;

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

@@ -30,6 +30,35 @@ help_to_synopsis () {
 	echo "$out"
 }
 
+builtin_to_txt () {
+       echo "$GIT_BUILD_DIR/Documentation/git-$1.txt"
+}
+
+txt_to_synopsis () {
+	builtin="$1" &&
+	out_dir="out/$builtin" &&
+	out="$out_dir/txt.synopsis" &&
+	if test -f "$out"
+	then
+		echo "$out" &&
+		return 0
+	fi &&
+	b2t="$(builtin_to_txt "$builtin")" &&
+	sed -n \
+		-e '/^\[verse\]$/,/^$/ {
+			/^$/d;
+			/^\[verse\]$/d;
+
+			p;
+		}' \
+		<"$b2t" >"$out" &&
+	echo "$out"
+}
+
+check_dashed_labels () {
+	! grep -E "<[^>_-]+_" "$1"
+}
+
 HT="	"
 
 while read builtin
@@ -39,6 +68,23 @@ do
 		h2s="$(help_to_synopsis "$builtin")" &&
 		! grep "$HT" "$h2s"
 	'
+
+	test_expect_success "$builtin -h output has dashed labels" '
+		check_dashed_labels "$(help_to_synopsis "$builtin")"
+	'
+
+	txt="$(builtin_to_txt "$builtin")" &&
+	preq="$(echo BUILTIN_TXT_$builtin | tr '[:lower:]-' '[:upper:]_')" &&
+
+	if test -f "$txt"
+	then
+		test_set_prereq "$preq"
+	fi &&
+
+	# *.txt output assertions
+	test_expect_success "$preq" "$builtin *.txt SYNOPSIS has dashed labels" '
+		check_dashed_labels "$(txt_to_synopsis "$builtin")"
+	'
 done <builtins
 
 test_done