[PATCH 3/3] Write index when populating empty untracked cache

From: Tao Klerks via GitGitGadget <gitgitgadget@gmail.com>
Date: Jun 24, 2021, 18:30 UTC
Message-ID: <627f1952fd8d4864b6b87f5539a9d9b802c5796b.1624559402.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.986.git.1624559401.gitgitgadget@gmail.com>

From: Tao Klerks <tao@klerks.biz>

It is expected that an empty/unpopulated untracked cache structure can be written to the index - by update- index, or by a "git status" call that sees the untracked cache should be enabled, but is running with options that make it non-applicable in that run.

Currently, if that happens, then subsequent "git status" calls end up populating the untracked cache, but not writing the index (not saving their work) - so the performance outcome is almost identical to the cache being altogether disabled.

This continues until the index gets written with the cache populated, for some *other* reason.

In this change, we detect the "existing cache is empty and it looks like we are using it" condition, and queues an index write when this happens.

This change depends on previous fixes to t7519 for the "ignore .git changes when invalidating UNTR" test case to pass - before this fix, the test never actually did anything as it was not set up correctly.

Signed-off-by: Tao Klerks <tao@klerks.biz>
---
 dir.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/dir.c b/dir.c
index ebe5ec046e0..a326e40e1c1 100644
--- a/dir.c
+++ b/dir.c
@@ -2703,7 +2703,8 @@ void remove_untracked_cache(struct index_state *istate)
 
 static struct untracked_cache_dir *validate_untracked_cache(struct dir_struct *dir,
 						      int base_len,
-						      const struct pathspec *pathspec)
+						      const struct pathspec *pathspec,
+						      struct index_state *istate)
 {
 	struct untracked_cache_dir *root;
 	static int untracked_cache_disabled = -1;
@@ -2767,8 +2768,15 @@ static struct untracked_cache_dir *validate_untracked_cache(struct dir_struct *d
 		return NULL;
 	}
 
-	if (!dir->untracked->root)
+	if (!dir->untracked->root) {
 		FLEX_ALLOC_STR(dir->untracked->root, name, "");
+		/*
+		 * If we've had to initialize the root, then what we had was an
+		 * empty uninitialized untracked cache structure. We will be
+		 * populating it now, so we should trigger an index write.
+		 */
+		istate->cache_changed |= UNTRACKED_CHANGED;
+	}
 
 	/* Validate $GIT_DIR/info/exclude and core.excludesfile */
 	root = dir->untracked->root;
@@ -2838,7 +2846,7 @@ int read_directory(struct dir_struct *dir, struct index_state *istate,
 		return dir->nr;
 	}
 
-	untracked = validate_untracked_cache(dir, len, pathspec);
+	untracked = validate_untracked_cache(dir, len, pathspec, istate);
 	if (!untracked)
 		/*
 		 * make sure untracked cache code path is disabled,

-- 
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