[GSoC][PATCH 1/4] path: add strbuf_add_path for formatting paths

[K Jayatheerth <jayatheerthkulkarni2005@gmail.com>]

The `print_path()` function in `builtin/rev-parse.c` contains
logic for formatting paths as either absolute or relative based on user
preferences and default behaviors. However, this logic is currently
locked inside `rev-parse` and writes directly to stdout using `puts()`.

To allow other builtins (such as the new `git repo` command) to utilize
this same path-formatting logic, extract the core algorithm into a new
string-builder function, `strbuf_add_path()`, in `path.c`.

Additionally, extract the associated enums (`format_type` and
`default_type`), and prefix them with `path_` (e.g., `path_format_type`)
to safely expose them in `path.h` without polluting the global namespace.

Signed-off-by: K Jayatheerth <jayatheerthkulkarni2005@gmail.com>
Mentored-by: Justin Tobler <jltobler@gmail.com>
Mentored-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
---
 path.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 path.h | 16 ++++++++++++++++
 2 files changed, 74 insertions(+)

diff --git a/path.c b/path.c
index d7e17bf174..914812320f 100644
--- a/path.c
+++ b/path.c
@@ -1579,6 +1579,64 @@ char *xdg_cache_home(const char *filename)
 	return NULL;
 }
 
+void strbuf_add_path(struct strbuf *sb, const char *path, const char *prefix,
+		     enum path_format_type format, enum path_default_type def)
+{
+	char *cwd = NULL;
+
+	/*
+	 * We don't ever produce a relative path if prefix is NULL, so set the
+	 * prefix to the current directory so that we can produce a relative
+	 * path whenever possible. If we're using RELATIVE_IF_SHARED mode, then
+	 * we want an absolute path unless the two share a common prefix, so don't
+	 * set it in that case, since doing so causes a relative path to always
+	 * be produced if possible.
+	 */
+	if (!prefix && (format != PATH_FORMAT_DEFAULT || def != PATH_DEFAULT_RELATIVE_IF_SHARED))
+		prefix = cwd = xgetcwd();
+
+	if (format == PATH_FORMAT_DEFAULT && def == PATH_DEFAULT_UNMODIFIED) {
+		/* Case 1: Return the path exactly as-is without modifications */
+		strbuf_addstr(sb, path);
+	} else if (format == PATH_FORMAT_RELATIVE ||
+		   (format == PATH_FORMAT_DEFAULT && def == PATH_DEFAULT_RELATIVE)) {
+		/*
+		 * Case 2: Explicitly or implicitly relative.
+		 * inside relative_path(), both targets must be absolute paths
+		 * to compute a reliable relative tracking offset.
+		 */
+		struct strbuf buf = STRBUF_INIT, realbuf = STRBUF_INIT, prefixbuf = STRBUF_INIT;
+
+		if (!is_absolute_path(path)) {
+			strbuf_realpath_forgiving(&realbuf, path, 1);
+			path = realbuf.buf;
+		}
+		if (!is_absolute_path(prefix)) {
+			strbuf_realpath_forgiving(&prefixbuf, prefix, 1);
+			prefix = prefixbuf.buf;
+		}
+
+		strbuf_addstr(sb, relative_path(path, prefix, &buf));
+
+		strbuf_release(&buf);
+		strbuf_release(&realbuf);
+		strbuf_release(&prefixbuf);
+	} else if (format == PATH_FORMAT_DEFAULT && def == PATH_DEFAULT_RELATIVE_IF_SHARED) {
+		/* Case 3: Relative format if they share a common root pathway */
+		struct strbuf buf = STRBUF_INIT;
+		strbuf_addstr(sb, relative_path(path, prefix, &buf));
+		strbuf_release(&buf);
+	} else {
+		/* Case 4: Forced absolute / canonical format optimization */
+		struct strbuf buf = STRBUF_INIT;
+		strbuf_realpath_forgiving(&buf, path, 1);
+		strbuf_addbuf(sb, &buf);
+		strbuf_release(&buf);
+	}
+
+	free(cwd);
+}
+
 REPO_GIT_PATH_FUNC(squash_msg, "SQUASH_MSG")
 REPO_GIT_PATH_FUNC(merge_msg, "MERGE_MSG")
 REPO_GIT_PATH_FUNC(merge_rr, "MERGE_RR")
diff --git a/path.h b/path.h
index 0434ba5e07..b9b626ce4a 100644
--- a/path.h
+++ b/path.h
@@ -262,6 +262,22 @@ enum scld_error safe_create_leading_directories_no_share(char *path);
 int safe_create_file_with_leading_directories(struct repository *repo,
 					      const char *path);
 
+enum path_format_type {
+	PATH_FORMAT_DEFAULT,
+	PATH_FORMAT_RELATIVE,
+	PATH_FORMAT_CANONICAL
+};
+
+enum path_default_type {
+	PATH_DEFAULT_RELATIVE,
+	PATH_DEFAULT_RELATIVE_IF_SHARED,
+	PATH_DEFAULT_CANONICAL,
+	PATH_DEFAULT_UNMODIFIED
+};
+
+void strbuf_add_path(struct strbuf *buf, const char *path, const char *prefix,
+		     enum path_format_type format, enum path_default_type def);
+
 # ifdef USE_THE_REPOSITORY_VARIABLE
 #  include "strbuf.h"
 #  include "repository.h"
-- 
2.54.0