t0450: add allowlist for builtins with missing .adoc

Before we were silently skipping all builtins that don't have a matching
.adoc file. This is overly loose and might skip documentation files
when it shouldn't, for example when there was a typo in the filename.

To ensure no new builtins are added without documentation, add an
allowlist: t0450/adoc-missing. In this file only builtin commands that
do *not* have a corresponding .adoc file shall be listed. If there is a
mismatch, fail the test. This should force future contributions to
either add an .adoc, or add the builtin name to the allowlist file.

Signed-off-by: Toon Claes <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: To1ne

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

@@ -112,10 +112,16 @@ do
 	adoc="$(builtin_to_adoc "$builtin")" &&
 	preq="$(echo BUILTIN_ADOC_$builtin | tr '[:lower:]-' '[:upper:]_')" &&
 
-	if test -f "$adoc"
+	# if and only if *.adoc is missing, builtin shall be listed in t0450/adoc-missing
+	result=success
+	if grep -q "^$builtin$" "$TEST_DIRECTORY"/t0450/adoc-missing
 	then
 		test_set_prereq "$preq"
+		result=failure
 	fi &&
+	test_expect_$result "$builtin appropriately marked as having missing .adoc" '
+		test -f "$adoc"
+	'
 
 	# *.adoc output assertions
 	test_expect_success "$preq" "$builtin *.adoc SYNOPSIS has dashed labels" '