[PATCH v6 1/2] setup: distinguish ENOENT from other stat errors

[Tian Yuchen <a3205153416@gmail.com>]

Currently, 'read_gitfile_gently()' treats all 'stat()' failures as
generic errors. This prevents distinguishing between a missing file and
real errors like permission denied (fatal).

Split 'READ_GITFILE_ERR_STAT_FAILED' into two:
 - 'READ_GITFILE_ERR_STAT_ENOENT': The file simply does not exist;
 - 'READ_GITFILE_ERR_STAT_FAILED': Real I/O or permission errors.

Introduce 'READ_GITFILE_ERR_IS_A_DIR':
 - Used when the path exists but is a directory.

Update 'read_gitfile_error_die()' to handle these cases:
 - Happy path ('ENOENT', 'IS_A_DIR'): Return without dying;
 - Fatal path ('STAT_FAILED', 'NOA_A_FILE'): Die immediately.

This prepares for error handling in the next commit.

Signed-off-by: Tian Yuchen <a3205153416@gmail.com>
---
 setup.c | 17 +++++++++++++----
 setup.h |  2 ++
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/setup.c b/setup.c
index c8336eb20e..d48b6a3a3d 100644
--- a/setup.c
+++ b/setup.c
@@ -897,10 +897,13 @@ int verify_repository_format(const struct repository_format *format,
 void read_gitfile_error_die(int error_code, const char *path, const char *dir)
 {
 	switch (error_code) {
+	case READ_GITFILE_ERR_STAT_ENOENT:
+	case READ_GITFILE_ERR_IS_A_DIR:
+		break;
 	case READ_GITFILE_ERR_STAT_FAILED:
+		die(_("error reading %s"), path);
 	case READ_GITFILE_ERR_NOT_A_FILE:
-		/* non-fatal; follow return path */
-		break;
+		die(_("not a regular file: %s"), path);
 	case READ_GITFILE_ERR_OPEN_FAILED:
 		die_errno(_("error opening '%s'"), path);
 	case READ_GITFILE_ERR_TOO_LARGE:
@@ -941,8 +944,14 @@ const char *read_gitfile_gently(const char *path, int *return_error_code)
 	static struct strbuf realpath = STRBUF_INIT;
 
 	if (stat(path, &st)) {
-		/* NEEDSWORK: discern between ENOENT vs other errors */
-		error_code = READ_GITFILE_ERR_STAT_FAILED;
+		if (errno == ENOENT)
+			error_code = READ_GITFILE_ERR_STAT_ENOENT;
+		else
+			error_code = READ_GITFILE_ERR_STAT_FAILED;
+		goto cleanup_return;
+	}
+	if (S_ISDIR(st.st_mode)) {
+		error_code = READ_GITFILE_ERR_IS_A_DIR;
 		goto cleanup_return;
 	}
 	if (!S_ISREG(st.st_mode)) {
diff --git a/setup.h b/setup.h
index 0738dec244..ed4b13f061 100644
--- a/setup.h
+++ b/setup.h
@@ -36,6 +36,8 @@ int is_nonbare_repository_dir(struct strbuf *path);
 #define READ_GITFILE_ERR_NO_PATH 6
 #define READ_GITFILE_ERR_NOT_A_REPO 7
 #define READ_GITFILE_ERR_TOO_LARGE 8
+#define READ_GITFILE_ERR_STAT_ENOENT 9
+#define READ_GITFILE_ERR_IS_A_DIR 10
 void read_gitfile_error_die(int error_code, const char *path, const char *dir);
 const char *read_gitfile_gently(const char *path, int *return_error_code);
 #define read_gitfile(path) read_gitfile_gently((path), NULL)
-- 
2.43.0