[PATCH v2 3/4] fsmonitor: avoid overriding `cache_changed` bits

From: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>
Date: Mar 26, 2023, 22:45 UTC
Message-ID: <89b3cd9a66823829ce6e425e827b70bc2816d3cd.1679870743.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.1497.v2.git.1679870743.gitgitgadget@gmail.com>

From: Johannes Schindelin <johannes.schindelin@gmx.de>

As of e636a7b4d030 (read-cache: be specific what part of the index has changed, 2014-06-13), the paradigm `cache_changed = 1` fell out of fashion and it became a bit field instead.

This is important because some bits have specific meaning and should not be unset without care, e.g. `SPLIT_INDEX_ORDERED`.

However, b5a816975206 (mark_fsmonitor_valid(): mark the index as changed if needed, 2019-05-24) did use the `cache_changed` attribute as if it were a Boolean instead of a bit field.

That not only would override the `SPLIT_INDEX_ORDERED` bit when marking index entries as valid via the FSMonitor, but worse: it would set the `SOMETHING_OTHER` bit (whose value is 1). This means that Git would unnecessarily force a full index to be written out when a split index was asked for.

Let's instead use the bit that is specifically intended to indicate FSMonitor-triggered changes, allowing the split-index feature to work as designed.

Noticed-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 fsmonitor.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fsmonitor.h b/fsmonitor.h
index edf7ce5203b..778707b131b 100644
--- a/fsmonitor.h
+++ b/fsmonitor.h
@@ -86,7 +86,7 @@ static inline void mark_fsmonitor_valid(struct index_state *istate, struct cache
 	    !(ce->ce_flags & CE_FSMONITOR_VALID)) {
 		if (S_ISGITLINK(ce->ce_mode))
 			return;
-		istate->cache_changed = 1;
+		istate->cache_changed |= FSMONITOR_CHANGED;
 		ce->ce_flags |= CE_FSMONITOR_VALID;
 		trace_printf_key(&trace_fsmonitor, "mark_fsmonitor_clean '%s'", ce->name);
 	}

-- 
gitgitgadget