[PATCH 13/14] tree-diff: simplify emit_path() list management

From: Jeff King <peff@peff.net>
Date: Jan 9, 2025, 08:54 UTC
Message-ID: <20250109085405.GM2748836@coredump.intra.peff.net>
In-Reply-To: <20250109082723.GA2748497@coredump.intra.peff.net>

In emit_path() we may append a new combine_diff_path entry to our list, decide that we don't want it (because opt->pathchange() told us so) and then roll it back.

Between the addition and the rollback, it doesn't matter if it's in the list or not (no functions can even tell, since it's a singly-linked list and we pass around just the tail entry).

So it's much simpler to just wait until opt->pathchange() tells us whether to keep it, and either attach it (or free it) then. We do still have to allocate it up front since it's that struct itself which is passed to the pathchange callback.

Signed-off-by: Jeff King <peff@peff.net>
---
 tree-diff.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/tree-diff.c b/tree-diff.c
index a1a611bef6..f5ec19113c 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -177,14 +177,12 @@ static struct combine_diff_path *emit_path(struct combine_diff_path *tail,
 
 	if (emitthis) {
 		int keep;
-		struct combine_diff_path *pprev = tail, *p;
+		struct combine_diff_path *p;
 
 		strbuf_add(base, path, pathlen);
 		p = combine_diff_path_new(base->buf, base->len, mode,
 					  oid ? oid : null_oid(),
 					  nparent);
-		tail->next = p;
-		tail = p;
 		strbuf_setlen(base, old_baselen);
 
 		for (i = 0; i < nparent; ++i) {
@@ -220,10 +218,11 @@ static struct combine_diff_path *emit_path(struct combine_diff_path *tail,
 		if (opt->pathchange)
 			keep = opt->pathchange(opt, p);
 
-		if (!keep) {
+		if (keep) {
+			tail->next = p;
+			tail = p;
+		} else {
 			free(p);
-			pprev->next = NULL;
-			tail = pprev;
 		}
 	}

-- 
2.48.0.rc2.413.gc1c80375a3