[PATCH v3 10/12] read-cache: drop explicit `CLOSE_LOCK`-flag

["Martin Ågren" <martin.agren@gmail.com>]

`write_locked_index()` takes two flags: `COMMIT_LOCK` and `CLOSE_LOCK`.
At most one is allowed. But it is also possible to use no flag, i.e.,
`0`. But when `write_locked_index()` calls `do_write_index()`, the
temporary file, a.k.a. the lockfile, will be closed. So passing `0` is
effectively the same as `CLOSE_LOCK`, which seems like a bug.

We might feel tempted to restructure the code in order to close the file
later, or conditionally. It also feels a bit unfortunate that we simply
"happen" to close the lock by way of an implementation detail of
lockfiles. But note that we need to close the temporary file before
`stat`-ing it, at least on Windows. See 9f41c7a6b (read-cache: close
index.lock in do_write_index, 2017-04-26).

Drop `CLOSE_LOCK` and make it explicit that `write_locked_index()`
always closes the lock. Whether it is also committed is governed by the
remaining flag, `COMMIT_LOCK`.

This means we neither have nor suggest that we have a mode to write the
index and leave the file open. Whatever extra contents we might
eventually want to write, we should probably write it from within
`write_locked_index()` itself anyway.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
---
v3: Dropped the comment in `do_write_locked_index()` and documented how
`do_write_index()` handles the temporary file instead.

 builtin/commit.c | 10 +++++-----
 cache.h          |  5 ++---
 read-cache.c     | 14 ++++++++------
 3 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index 0f8ddb686..32dc2101f 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -355,7 +355,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 
 		refresh_cache_or_die(refresh_flags);
 
-		if (write_locked_index(&the_index, &index_lock, CLOSE_LOCK))
+		if (write_locked_index(&the_index, &index_lock, 0))
 			die(_("unable to create temporary index"));
 
 		old_index_env = getenv(INDEX_ENVIRONMENT);
@@ -374,7 +374,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 		if (update_main_cache_tree(WRITE_TREE_SILENT) == 0) {
 			if (reopen_lock_file(&index_lock) < 0)
 				die(_("unable to write index file"));
-			if (write_locked_index(&the_index, &index_lock, CLOSE_LOCK))
+			if (write_locked_index(&the_index, &index_lock, 0))
 				die(_("unable to update temporary index"));
 		} else
 			warning(_("Failed to update main cache tree"));
@@ -401,7 +401,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 		add_files_to_cache(also ? prefix : NULL, &pathspec, 0);
 		refresh_cache_or_die(refresh_flags);
 		update_main_cache_tree(WRITE_TREE_SILENT);
-		if (write_locked_index(&the_index, &index_lock, CLOSE_LOCK))
+		if (write_locked_index(&the_index, &index_lock, 0))
 			die(_("unable to write new_index file"));
 		commit_style = COMMIT_NORMAL;
 		ret = get_lock_file_path(&index_lock);
@@ -474,7 +474,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 	add_remove_files(&partial);
 	refresh_cache(REFRESH_QUIET);
 	update_main_cache_tree(WRITE_TREE_SILENT);
-	if (write_locked_index(&the_index, &index_lock, CLOSE_LOCK))
+	if (write_locked_index(&the_index, &index_lock, 0))
 		die(_("unable to write new_index file"));
 
 	hold_lock_file_for_update(&false_lock,
@@ -486,7 +486,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
 	add_remove_files(&partial);
 	refresh_cache(REFRESH_QUIET);
 
-	if (write_locked_index(&the_index, &false_lock, CLOSE_LOCK))
+	if (write_locked_index(&the_index, &false_lock, 0))
 		die(_("unable to write temporary index file"));
 
 	discard_cache();
diff --git a/cache.h b/cache.h
index e9d9556e3..21a6856c5 100644
--- a/cache.h
+++ b/cache.h
@@ -604,11 +604,10 @@ extern int read_index_unmerged(struct index_state *);
 
 /* For use with `write_locked_index()`. */
 #define COMMIT_LOCK		(1 << 0)
-#define CLOSE_LOCK		(1 << 1)
 
 /*
- * Write the index while holding an already-taken lock. The flags may
- * contain at most one of `COMMIT_LOCK` and `CLOSE_LOCK`.
+ * Write the index while holding an already-taken lock. Close the lock,
+ * and if `COMMIT_LOCK` is given, commit it.
  *
  * Unless a split index is in use, write the index into the lockfile.
  *
diff --git a/read-cache.c b/read-cache.c
index 65f4fe837..c7aa3632a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2187,6 +2187,13 @@ void update_index_if_able(struct index_state *istate, struct lock_file *lockfile
 		rollback_lock_file(lockfile);
 }
 
+/*
+ * On success, `tempfile` is closed. If it is the temporary file
+ * of a `struct lock_file`, we will therefore effectively perform
+ * a 'close_lock_file_gently()`. Since that is an implementation
+ * detail of lockfiles, callers of `do_write_index()` should not
+ * rely on it.
+ */
 static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 			  int strip_extensions)
 {
@@ -2343,14 +2350,9 @@ static int do_write_locked_index(struct index_state *istate, struct lock_file *l
 	int ret = do_write_index(istate, lock->tempfile, 0);
 	if (ret)
 		return ret;
-	assert((flags & (COMMIT_LOCK | CLOSE_LOCK)) !=
-	       (COMMIT_LOCK | CLOSE_LOCK));
 	if (flags & COMMIT_LOCK)
 		return commit_locked_index(lock);
-	else if (flags & CLOSE_LOCK)
-		return close_lock_file_gently(lock);
-	else
-		return ret;
+	return close_lock_file_gently(lock);
 }
 
 static int write_split_index(struct index_state *istate,
-- 
2.15.0.rc0