[v3,5/5] interpolate_path(): allow specifying paths relative to the runtime prefix

Commit Message

Johannes Schindelin July 24, 2021, 10:06 p.m. UTC

From: Johannes Schindelin <[e-mail]>

Ever since Git learned to detect its install location at runtime, there
was the slightly awkward problem that it was impossible to specify paths
relative to said location.

For example, if a version of Git was shipped with custom SSL
certificates to use, there was no portable way to specify
`http.sslCAInfo`.

In Git for Windows, the problem was "solved" for years by interpreting
paths starting with a slash as relative to the runtime prefix.

However, this is not correct: such paths _are_ legal on Windows, and
they are interpreted as absolute paths in the same drive as the current
directory.

After a lengthy discussion, and an even lengthier time to mull over the
problem and its best solution, and then more discussions, we eventually
decided to introduce support for the magic sequence `%(prefix)/`. If a
path starts with this, the remainder is interpreted as relative to the
detected (runtime) prefix. If built without runtime prefix support, Git
will simply interpolate the compiled-in prefix.

If a user _wants_ to specify a path starting with the magic sequence,
they can prefix the magic sequence with `./` and voilà, the path won't
be expanded.

Signed-off-by: Johannes Schindelin <[e-mail]>
---
 Documentation/config.txt | 9 +++++++++
 path.c                   | 8 ++++++++
 t/t0060-path-utils.sh    | 8 ++++++++
 3 files changed, 25 insertions(+)

Patch

diff --git a/Documentation/config.txt b/Documentation/config.txt
index bf82766a6a2..0c0e6b859f1 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -298,6 +298,15 @@  pathname::
 	tilde expansion happens to such a string: `~/`
 	is expanded to the value of `$HOME`, and `~user/` to the
 	specified user's home directory.
++
+If a path starts with `%(prefix)/`, the remainder is interpreted as a
+path relative to Git's "runtime prefix", i.e. relative to the location
+where Git itself was installed. For example, `%(prefix)/bin/` refers to
+the directory in which the Git executable itself lives. If Git was
+compiled without runtime prefix support, the compiled-in prefix will be
+subsituted instead. In the unlikely event that a literal path needs to
+be specified that should _not_ be expanded, it needs to be prefixed by
+`./`, like so: `./%(prefix)/bin`.
 
 
 Variables
diff --git a/path.c b/path.c
index 8dc5ad2cb55..0bc788ea40f 100644
--- a/path.c
+++ b/path.c
@@ -12,6 +12,7 @@ 
 #include "packfile.h"
 #include "object-store.h"
 #include "lockfile.h"
+#include "exec-cmd.h"
 
 static int get_st_mode_bits(const char *path, int *mode)
 {
@@ -723,6 +724,9 @@  static struct passwd *getpw_str(const char *username, size_t len)
  * failure or if path is NULL.
  *
  * If real_home is true, strbuf_realpath($HOME) is used in the `~/` expansion.
+ *
+ * If the path starts with `%(prefix)/`, the remainder is interpreted as
+ * relative to where Git is installed, and expanded to the absolute path.
  */
 char *interpolate_path(const char *path, int real_home)
 {
@@ -731,6 +735,10 @@  char *interpolate_path(const char *path, int real_home)
 
 	if (path == NULL)
 		goto return_null;
+
+	if (skip_prefix(path, "%(prefix)/", &path))
+		return system_path(path);
+
 	if (path[0] == '~') {
 		const char *first_slash = strchrnul(path, '/');
 		const char *username = path + 1;
diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index a76728c27bf..34d1061f321 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -540,6 +540,14 @@  test_expect_success RUNTIME_PREFIX,CAN_EXEC_IN_PWD 'RUNTIME_PREFIX works' '
 	cp "$GIT_EXEC_PATH"/git$X pretend/bin/ &&
 	GIT_EXEC_PATH= ./pretend/bin/git here >actual &&
 	echo HERE >expect &&
+	test_cmp expect actual'
+
+test_expect_success RUNTIME_PREFIX,CAN_EXEC_IN_PWD '%(prefix)/ works' '
+	mkdir -p pretend/bin &&
+	cp "$GIT_EXEC_PATH"/git$X pretend/bin/ &&
+	git config yes.path "%(prefix)/yes" &&
+	GIT_EXEC_PATH= ./pretend/bin/git config --path yes.path >actual &&
+	echo "$(pwd)/pretend/yes" >expect &&
 	test_cmp expect actual
 '