fsck: test & document {fetch,receive}.fsck.* config fallback

Test and document that the {fetch,receive}.fsck.* family of variables
doesn't fall back on the corresponding .fsck.* variables.

This was alluded to in the existing documentation by saying that
"receive" looks at receive.fsck.* and "fsck" looks at fsck.* etc., but
it wasn't explicitly stated that there was no fallback, and if you'd
e.g. like to configure the skipList you need to do that for all three.

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

Documentation/config.txt

@@ -1619,6 +1619,12 @@ The rest of the documentation discusses `fsck.*` for brevity, but the
 same applies for the corresponding `receive.fsck.*` and
 `fetch.<msg-id>.*`. variables.
 +
+Unlike variables like `color.ui` and `core.editor` the
+`receive.fsck.<msg-id>` and `fetch.fsck.<msg-id>` variables will not
+fall back on the `fsck.<msg-id>` configuration if they aren't set. To
+uniformly configure the same fsck settings in different circumstances
+all three of them they must all set to the same values.
++
 When `fsck.<msg-id>` is set, errors can be switched to warnings and
 vice versa by configuring the `fsck.<msg-id>` setting where the
 `<msg-id>` is the fsck message ID and the value is one of `error`,
@@ -1642,6 +1648,12 @@ fsck.skipList::
 +
 Like `fsck.<msg-id>` this variable has corresponding
 `receive.fsck.skipList` and `fetch.fsck.skipList` variants.
++
+Unlike variables like `color.ui` and `core.editor` the
+`receive.fsck.skipList` and `fetch.fsck.skipList` variables will not
+fall back on the `fsck.skipList` configuration if they aren't set. To
+uniformly configure the same fsck settings in different circumstances
+all three of them they must all set to the same values.
 
 gc.aggressiveDepth::
 	The depth parameter used in the delta compression

t/t5504-fetch-receive-strict.sh

@@ -140,8 +140,13 @@ test_expect_success 'push with receive.fsck.skipList' '
 	git init dst &&
 	git --git-dir=dst/.git config receive.fsckObjects true &&
 	test_must_fail git push --porcelain dst bogus &&
-	git --git-dir=dst/.git config receive.fsck.skipList SKIP &&
 	echo $commit >dst/.git/SKIP &&
+
+	# receive.fsck.* does not fall back on fsck.*
+	git --git-dir=dst/.git config fsck.skipList SKIP &&
+	test_must_fail git push --porcelain dst bogus &&
+
+	git --git-dir=dst/.git config receive.fsck.skipList SKIP &&
 	git push --porcelain dst bogus
 '
 
@@ -153,8 +158,15 @@ test_expect_success 'fetch with fetch.fsck.skipList' '
 	git init dst &&
 	git --git-dir=dst/.git config fetch.fsckObjects true &&
 	test_must_fail git --git-dir=dst/.git fetch "file://$(pwd)" $refspec &&
-	git --git-dir=dst/.git config fetch.fsck.skipList dst/.git/SKIP &&
+	git --git-dir=dst/.git config fetch.fsck.skipList /dev/null &&
+	test_must_fail git --git-dir=dst/.git fetch "file://$(pwd)" $refspec &&
 	echo $commit >dst/.git/SKIP &&
+
+	# fetch.fsck.* does not fall back on fsck.*
+	git --git-dir=dst/.git config fsck.skipList dst/.git/SKIP &&
+	test_must_fail git --git-dir=dst/.git fetch "file://$(pwd)" $refspec &&
+
+	git --git-dir=dst/.git config fetch.fsck.skipList dst/.git/SKIP &&
 	git --git-dir=dst/.git fetch "file://$(pwd)" $refspec
 '
 
@@ -166,6 +178,11 @@ test_expect_success 'push with receive.fsck.missingEmail=warn' '
 	git init dst &&
 	git --git-dir=dst/.git config receive.fsckobjects true &&
 	test_must_fail git push --porcelain dst bogus &&
+
+	# receive.fsck.<msg-id> does not fall back on fsck.<msg-id>
+	git --git-dir=dst/.git config fsck.missingEmail warn &&
+	test_must_fail git push --porcelain dst bogus &&
+
 	git --git-dir=dst/.git config \
 		receive.fsck.missingEmail warn &&
 	git push --porcelain dst bogus >act 2>&1 &&
@@ -185,6 +202,11 @@ test_expect_success 'fetch with fetch.fsck.missingEmail=warn' '
 	git init dst &&
 	git --git-dir=dst/.git config fetch.fsckobjects true &&
 	test_must_fail git --git-dir=dst/.git fetch "file://$(pwd)" $refspec &&
+
+	# fetch.fsck.<msg-id> does not fall back on fsck.<msg-id>
+	git --git-dir=dst/.git config fsck.missingEmail warn &&
+	test_must_fail git --git-dir=dst/.git fetch "file://$(pwd)" $refspec &&
+
 	git --git-dir=dst/.git config \
 		fetch.fsck.missingEmail warn &&
 	git --git-dir=dst/.git fetch "file://$(pwd)" $refspec >act 2>&1 &&