[GSoC Patch v8 1/3] path: extract format_path() and use in rev-parse

[K Jayatheerth <jayatheerthkulkarni2005@gmail.com>]

Path formatting logic in builtin/rev-parse.c writes directly to
stdout. Other builtins cannot reuse it.

Extract this logic into format_path() in path.c and expose
a path_format enum in path.h.

Convert rev-parse to use the new helper in the same step to validate
the API against existing tests and avoid introducing dead code.

Mentored-by: Justin Tobler <jltobler@gmail.com>
Mentored-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
Signed-off-by: K Jayatheerth <jayatheerthkulkarni2005@gmail.com>
---
 builtin/rev-parse.c | 79 +++++++++++++++++++++------------------------
 path.c              | 69 +++++++++++++++++++++++++++++++++++++++
 path.h              | 30 +++++++++++++++++
 3 files changed, 135 insertions(+), 43 deletions(-)

diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index bb882678fe..7d6ac92038 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -653,53 +653,46 @@ enum default_type {
 	DEFAULT_UNMODIFIED,
 };
 
-static void print_path(const char *path, const char *prefix, enum format_type format, enum default_type def)
+static void print_path(const char *path, const char *prefix,
+		       enum format_type format, enum 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 != FORMAT_DEFAULT || def != DEFAULT_RELATIVE_IF_SHARED))
-		prefix = cwd = xgetcwd();
-	if (format == FORMAT_DEFAULT && def == DEFAULT_UNMODIFIED) {
-		puts(path);
-	} else if (format == FORMAT_RELATIVE ||
-		  (format == FORMAT_DEFAULT && def == DEFAULT_RELATIVE)) {
-		/*
-		 * In order for relative_path to work as expected, we need to
-		 * make sure that both paths are absolute paths.  If we don't,
-		 * we can end up with an unexpected absolute path that the user
-		 * didn't want.
-		 */
-		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;
+	struct strbuf sb = STRBUF_INIT;
+	enum path_format fmt;
+
+	if (format == FORMAT_DEFAULT) {
+		switch (def) {
+		case DEFAULT_RELATIVE:
+			fmt = PATH_FORMAT_RELATIVE;
+			break;
+		case DEFAULT_RELATIVE_IF_SHARED:
+			fmt = PATH_FORMAT_RELATIVE_IF_SHARED;
+			break;
+		case DEFAULT_CANONICAL:
+			fmt = PATH_FORMAT_CANONICAL;
+			break;
+		case DEFAULT_UNMODIFIED:
+		default:
+			fmt = PATH_FORMAT_UNMODIFIED;
+			break;
 		}
-		puts(relative_path(path, prefix, &buf));
-		strbuf_release(&buf);
-		strbuf_release(&realbuf);
-		strbuf_release(&prefixbuf);
-	} else if (format == FORMAT_DEFAULT && def == DEFAULT_RELATIVE_IF_SHARED) {
-		struct strbuf buf = STRBUF_INIT;
-		puts(relative_path(path, prefix, &buf));
-		strbuf_release(&buf);
 	} else {
-		struct strbuf buf = STRBUF_INIT;
-		strbuf_realpath_forgiving(&buf, path, 1);
-		puts(buf.buf);
-		strbuf_release(&buf);
+		switch (format) {
+		case FORMAT_RELATIVE:
+			fmt = PATH_FORMAT_RELATIVE;
+			break;
+		case FORMAT_CANONICAL:
+			fmt = PATH_FORMAT_CANONICAL;
+			break;
+		default:
+			fmt = PATH_FORMAT_UNMODIFIED;
+			break;
+		}
 	}
-	free(cwd);
+
+	format_path(&sb, path, prefix, fmt);
+	puts(sb.buf);
+
+	strbuf_release(&sb);
 }
 
 int cmd_rev_parse(int argc,
diff --git a/path.c b/path.c
index d7e17bf174..c3a709a928 100644
--- a/path.c
+++ b/path.c
@@ -1579,6 +1579,75 @@ char *xdg_cache_home(const char *filename)
 	return NULL;
 }
 
+void format_path(struct strbuf *dest, const char *path,
+		 const char *prefix, enum path_format format)
+{
+	strbuf_reset(dest);
+
+	switch (format) {
+	case PATH_FORMAT_UNMODIFIED:
+		strbuf_addstr(dest, path);
+		break;
+
+	case PATH_FORMAT_RELATIVE: {
+		struct strbuf relative_buf = STRBUF_INIT;
+		struct strbuf real_path = STRBUF_INIT;
+		struct strbuf real_prefix = STRBUF_INIT;
+		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 (!prefix)
+			prefix = cwd = xgetcwd();
+
+		if (!is_absolute_path(path)) {
+			strbuf_realpath_forgiving(&real_path, path, 1);
+			path = real_path.buf;
+		}
+		if (!is_absolute_path(prefix)) {
+			strbuf_realpath_forgiving(&real_prefix, prefix, 1);
+			prefix = real_prefix.buf;
+		}
+
+		strbuf_addstr(dest, relative_path(path, prefix, &relative_buf));
+
+		strbuf_release(&relative_buf);
+		strbuf_release(&real_path);
+		strbuf_release(&real_prefix);
+		free(cwd);
+		break;
+	}
+
+	case PATH_FORMAT_RELATIVE_IF_SHARED: {
+		struct strbuf relative_buf = STRBUF_INIT;
+
+		/*
+		 * If we're using RELATIVE_IF_SHARED mode, then we want an
+		 * absolute path unless the two share a common prefix, so don't
+		 * default the prefix to the current working directory. Doing so
+		 * would cause a relative path to always be produced if possible.
+		 */
+		strbuf_addstr(dest, relative_path(path, prefix, &relative_buf));
+		strbuf_release(&relative_buf);
+		break;
+	}
+
+	case PATH_FORMAT_CANONICAL:
+		/*
+		 * strbuf_realpath_forgiving inherently resets the destination
+		 * buffer, safely aligning with our replace semantics.
+		 */
+		strbuf_realpath_forgiving(dest, path, 1);
+		break;
+
+	default:
+		BUG("unknown path_format value %d", format);
+	}
+}
+
 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 4c2958a903..7e7408dd05 100644
--- a/path.h
+++ b/path.h
@@ -262,6 +262,36 @@ enum scld_error safe_create_leading_directories_no_share(char *path);
 int safe_create_file_with_leading_directories(struct repository *repo,
 					      const char *path);
 
+/**
+ * The formatting strategy to apply when writing a path into a buffer.
+ */
+enum path_format {
+	/* Output the path exactly as-is without any modifications. */
+	PATH_FORMAT_UNMODIFIED,
+
+	/* Output a path relative to the provided directory prefix. */
+	PATH_FORMAT_RELATIVE,
+
+	/* Output a relative path only if the path shares a root with the prefix. */
+	PATH_FORMAT_RELATIVE_IF_SHARED,
+
+	/* Output a fully resolved, absolute canonical path. */
+	PATH_FORMAT_CANONICAL
+};
+
+/**
+ * Format a path according to the specified formatting strategy and store
+ * the result in the given strbuf, replacing any existing contents.
+ *
+ * `dest`   : The string buffer to store the formatted path into.
+ * `path`   : The path string that needs to be formatted.
+ * `prefix` : The directory prefix to calculate relative offsets against.
+ * Pass NULL to default to the current working directory where applicable.
+ * `format` : The formatting behavior rule to execute.
+ */
+void format_path(struct strbuf *dest, const char *path,
+		 const char *prefix, enum path_format format);
+
 # ifdef USE_THE_REPOSITORY_VARIABLE
 #  include "strbuf.h"
 #  include "repository.h"
-- 
2.55.0-rc1