Re: [PATCH v6 1/1] config: add conditional include

Signed-off-by: Nguyễn Thái Ngọc Duy <redacted>
---
 Documentation/config.txt  | 61 +++++++++++++++++++++++++++++
 config.c                  | 97 +++++++++++++++++++++++++++++++++++++++++++++++
 t/t1305-config-include.sh | 56 +++++++++++++++++++++++++++
 3 files changed, 214 insertions(+)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 015346c417..6c0cd2a273 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt

@@ -91,6 +91,56 @@ found at the location of the include directive. If the value of the
 relative to the configuration file in which the include directive was
 found.  See below for examples.
 
+Conditional includes
+~~~~~~~~~~~~~~~~~~~~
+
+You can include one config file from another conditionally by setting
+a `includeIf.<condition>.path` variable to the name of the file to be
+included. The variable's value is treated the same way as `include.path`.
+
+The condition starts with a keyword followed by a colon and some data
+whose format and meaning depends on the keyword. Supported keywords
+are:
+
+`gitdir`::
+
+	The data that follows the keyword `gitdir:` is used as a glob
+	pattern. If the location of the .git directory match the
+	pattern, the include condition is met.
++
+The .git location which may be auto-discovered, or come from
+`$GIT_DIR` environment variable. If the repository auto discovered via
+a .git file (e.g. from submodules, or a linked worktree), the .git
+location would be the final location, not where the .git file is.
++
+The pattern can contain standard globbing wildcards and two additional
+ones, `**/` and `/**`, that can match multiple path components. Please
+refer to linkgit:gitignore[5] for details. For convenience:
+
+ * If the pattern starts with `~/`, `~` will be substituted with the
+   content of the environment variable `HOME`.
+
+ * If the pattern starts with `./`, it is replaced with the directory
+   containing the current config file.
+
+ * If the pattern does not start with either `~/`, `./` or `/`, `**/`
+   will be automatically prepended. For example, the pattern `foo/bar`
+   becomes `**/foo/bar` and would match `/any/path/to/foo/bar`.
+
+ * If the pattern ends with `/`, `**` will be automatically added. For
+   example, the pattern `foo/` becomes `foo/**`. In other words, it
+   matches "foo" and everything inside, recursively.
+
+`gitdir/i`::
+	This is the same as `gitdir` except that matching is done
+	case-insensitively (e.g. on case-insensitive file sytems)
+
+A few more notes on matching with `gitdir` and `gitdir/i`:
+
+ * Symlinks in `$GIT_DIR` are not resolved before matching.
+
+ * Note that "../" is not special and will match literally, which is
+   unlikely what you want.
 
 Example
 ~~~~~~~

@@ -119,6 +169,17 @@ Example
 		path = foo ; expand "foo" relative to the current file
 		path = ~/foo ; expand "foo" in your `$HOME` directory
 
+	; include if $GIT_DIR is /path/to/foo/.git
+	[include-if "gitdir:/path/to/foo/.git"]