[RFC] git-config-batch: a new builtin for tools reading config

.gitignore

@@ -44,6 +44,7 @@
 /git-commit-graph
 /git-commit-tree
 /git-config
+/git-config-batch
 /git-count-objects
 /git-credential
 /git-credential-cache

Documentation/git-config-batch.adoc

@@ -0,0 +1,109 @@
+git-config-batch(1)
+===================
+
+NAME
+----
+git-config-batch - Get and set options using machine-parseable interface
+
+
+SYNOPSIS
+--------
+[verse]
+'git config-batch' <options>
+
+DESCRIPTION
+-----------
+Tools frequently need to change their behavior based on values stored in
+Git's configuration files. These files may have complicated conditions
+for including extra files, so it is difficult to produce an independent
+parser. To avoid executing multiple processes to discover or modify
+multiple configuration values, the `git config-batch` command allows a
+single process to handle multiple requests using a machine-parseable
+interface across `stdin` and `stdout`.
+
+PROTOCOL
+--------
+By default, the protocol uses line feeds (`LF`) to signal the end of a
+command over `stdin` or a response over `stdout`.
+
+The protocol will be extended in the future, and consumers should be
+resilient to older Git versions not understanding the latest command
+set. Thus, if the Git version includes the `git config-batch` builtin
+but doesn't understand an input command, it will return a single line
+response:
+
+------------
+unknown_command LF
+------------
+
+These are the commands that are currently understood:
+
+`help` version 1::
+	The `help` command lists the currently-available commands in
+	this version of Git. The output is multi-line, but the first
+	line provides the count of possible commands via `help count <N>`.
+	The next `<N>` lines are of the form `help <command> <version>`
+	to state that this Git version supports that `<command>` at
+	version `<version>`. Note that the same command may have multiple
+	available versions.
++
+Here is the currentl output of the help text at the latest version:
++
+------------
+help count 2
+help help 1
+help get 1
+------------
+
+`get` version 1::
+	The `get` command searches the config key-value pairs within a
+	given `<scope>` for values that match the fixed `<key>` and
+	filters the resulting value based on an optional `<value-filter>`.
+	This can either be a regex or a fixed value. The command format
+	is one of the following formats:
++
+------------
+get 1 <scope> <key>
+get 1 <scope> <key> regex <value-pattern>
+get 1 <scope> <key> fixed-value <value>
+------------
++
+The `<scope>` value can be one of `inherited`, `system`, `global`,
+`local`, `worktree`, `submodule`, or `command`. If `inherited`, then all
+config key-value pairs will be considered regardless of scope. Otherwise,
+only the given scope will be considered.
++
+If no optional arguments are given, then the value will not be filtered
+by any pattern matching. If `regex` is specified, then `<value-pattern>`
+is interpreted as a regular expression for matching against stored
+values, similar to specifying a value to `get config --get <key> <value>`.
+If `fixed-value` is specified, then `<value>` is checked for an exact
+match against the key-value pairs, simmilar to `git config --get <key>
+--fixed-value <value>`.
++
+At mmost one key-value pair is returned, that being the last key-value
+pair in the standard config order by scope and sequence within each scope.
++
+If a key-value pair is found, then the following output is given:
++
+------------
+get found <key> <scope> <value>
+------------
++
+If no matching key-value pair is found, then the following output is
+given:
++
+------------
+get missing <key> [<value-pattern>|<value>]
+------------
++
+where `<value-pattern>` or `<value>` is only supplied if provided in
+the command.
+
+SEE ALSO
+--------
+linkgit:git-config[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite

Makefile

@@ -1390,6 +1390,7 @@ BUILTIN_OBJS += builtin/commit-graph.o
 BUILTIN_OBJS += builtin/commit-tree.o
 BUILTIN_OBJS += builtin/commit.o
 BUILTIN_OBJS += builtin/config.o
+BUILTIN_OBJS += builtin/config-batch.o
 BUILTIN_OBJS += builtin/count-objects.o
 BUILTIN_OBJS += builtin/credential-cache--daemon.o
 BUILTIN_OBJS += builtin/credential-cache.o

builtin.h

@@ -68,10 +68,14 @@
  *
  * . Add `builtin/foo.o` to `BUILTIN_OBJS` in `Makefile`.
  *
+ * . Add 'builtin/foo.c' to the 'builtin_sources' array in 'meson.build'.
+ *
  * Additionally, if `foo` is a new command, there are 4 more things to do:
  *
  * . Add tests to `t/` directory.
  *
+ * . Add the test script to 'integration_tests' in  't/meson.build'.
+ *
  * . Write documentation in `Documentation/git-foo.adoc`.
  *
  * . Add an entry for `git-foo` to `command-list.txt`.
@@ -167,6 +171,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix, struct repositor
 int cmd_commit_graph(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_commit_tree(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_config(int argc, const char **argv, const char *prefix, struct repository *repo);
+int cmd_config_batch(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_count_objects(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_credential(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_credential_cache(int argc, const char **argv, const char *prefix, struct repository *repo);