docs/gitcredentials: describe URL prefix matching

Documentation was inaccurate since 9a121b0 (credential: handle
`credential.<partial-URL>.<key>` again, 2020-04-24)

Add tests for documented behaviour.

Signed-off-by: M Hickford <mirth.hickford@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: hickford

Documentation/gitcredentials.txt

@@ -133,9 +133,8 @@ pattern in the config file. For example, if you have this in your config file:
 	username = foo
 --------------------------------------
 
-then we will match: both protocols are the same, both hosts are the same, and
-the "pattern" URL does not care about the path component at all. However, this
-context would not match:
+then we will match: both protocols are the same and both hosts are the same.
+However, this context would not match:
 
 --------------------------------------
 [credential "https://kernel.org"]
@@ -149,11 +148,11 @@ match: Git compares the protocols exactly.  However, you may use wildcards in
 the domain name and other pattern matching techniques as with the `http.<URL>.*`
 options.
 
-If the "pattern" URL does include a path component, then this too must match
-exactly: the context `https://example.com/bar/baz.git` will match a config
-entry for `https://example.com/bar/baz.git` (in addition to matching the config
-entry for `https://example.com`) but will not match a config entry for
-`https://example.com/bar`.
+If the "pattern" URL does include a path component, then this must match
+as a prefix path: the context `https://example.com/bar` will match a config
+entry for `https://example.com/bar/baz.git` but will not match a config entry for
+`https://example.com/other/repo.git` or `https://example.com/barry/repo.git`
+(even though it is a string prefix).
 
 
 CONFIGURATION OPTIONS

t/t0300-credentials.sh

@@ -991,18 +991,24 @@ test_expect_success 'url parser not confused by encoded markers' '
 
 test_expect_success 'credential config with partial URLs' '
 	echo "echo password=yep" | write_script git-credential-yep &&
-	test_write_lines url=https://user@example.com/repo.git >stdin &&
+	test_write_lines url=https://user@example.com/org/repo.git >stdin &&
 	for partial in \
 		example.com \
+		example.com/org/repo.git \
 		user@example.com \
+		user@example.com/org/repo.git \
 		https:// \
 		https://example.com \
 		https://example.com/ \
+		https://example.com/org \
+		https://example.com/org/ \
+		https://example.com/org/repo.git \
 		https://user@example.com \
 		https://user@example.com/ \
-		https://example.com/repo.git \
-		https://user@example.com/repo.git \
-		/repo.git
+		https://user@example.com/org \
+		https://user@example.com/org/ \
+		https://user@example.com/org/repo.git \
+		/org/repo.git
 	do
 		git -c credential.$partial.helper=yep \
 			credential fill <stdin >stdout &&
@@ -1012,7 +1018,12 @@ test_expect_success 'credential config with partial URLs' '
 
 	for partial in \
 		dont.use.this \
+		example.com/o \
+		user@example.com/o \
 		http:// \
+		https://example.com/o \
+		https://user@example.com/o \
+		/o \
 		/repo
 	do
 		git -c credential.$partial.helper=yep \