config: include file if remote URL matches a glob

This is a feature that supports config file inclusion conditional on
whether the repo has a remote with a URL that matches a glob.

Similar to my previous work on remote-suggested hooks [1], the main
motivation is to allow remote repo administrators to provide recommended
configs in a way that can be consumed more easily (e.g. through a
package installable by a package manager - it could, for example,
contain a file to be included conditionally and a post-install script
that adds the include directive to the system-wide config file).

In order to do this, Git reruns the config parsing mechanism upon
noticing the first URL-conditional include in order to find all remote
URLs, and these remote URLs are then used to determine if that first and
all subsequent includes are executed. Remote URLs are not allowed to be
configued in any URL-conditionally-included file.

[1] https://lore.kernel.org/git/cover.1623881977.git.jonathantanmy@google.com/

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Acked-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 1167e88..0b8929b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -159,6 +159,33 @@ all branches that begin with `foo/`. This is useful if your branches are
 organized hierarchically and you would like to apply a configuration to
 all the branches in that hierarchy.
 
+`hasconfig:remote.*.url:`::
+	The data that follows this keyword is taken to
+	be a pattern with standard globbing wildcards and two
+	additional ones, `**/` and `/**`, that can match multiple
+	components. The first time this keyword is seen, the rest of
+	the config files will be scanned for remote URLs (without
+	applying any values). If there exists at least one remote URL
+	that matches this pattern, the include condition is met.
++
+Files included by this option (directly or indirectly) are not allowed
+to contain remote URLs.
++
+Note that unlike other includeIf conditions, resolving this condition
+relies on information that is not yet known at the point of reading the
+condition. A typical use case is this option being present as a
+system-level or global-level config, and the remote URL being in a
+local-level config; hence the need to scan ahead when resolving this
+condition. In order to avoid the chicken-and-egg problem in which
+potentially-included files can affect whether such files are potentially
+included, Git breaks the cycle by prohibiting these files from affecting
+the resolution of these conditions (thus, prohibiting them from
+declaring remote URLs).
++
+As for the naming of this keyword, it is for forwards compatibiliy with
+a naming scheme that supports more variable-based include conditions,
+but currently Git only supports the exact keyword described above.
+
 A few more notes on matching via `gitdir` and `gitdir/i`:
 
  * Symlinks in `$GIT_DIR` are not resolved before matching.
@@ -226,6 +253,14 @@ Example
 ; currently checked out
 [includeIf "onbranch:foo-branch"]
 	path = foo.inc
+
+; include only if a remote with the given URL exists (note
+; that such a URL may be provided later in a file or in a
+; file read after this file is read, as seen in this example)
+[includeIf "hasconfig:remote.*.url:https://example.com/**"]
+	path = foo.inc
+[remote "origin"]
+	url = https://example.com/git
 ----
 
 Values