[PATCH v2] patch-ids: document intentional const-casting in patch_id_neq()
- From
Tian Yuchen <cat@malon.dev>
- Date
- Mar 8, 2026, 15:02 UTC
- Message-ID
- <20260308150203.86299-1-cat@malon.dev>
- In-Reply-To
- <20260308043131.77782-1-a3205153416@gmail.com>
The hashmap API requires the comparison function to take const pointers. However, patch_id_neq() uses lazy evaluation to compute patch IDs on demand.
Pre-calculating all patch IDs to achieve true const correctness would introduce an unacceptable performance penalty.
Remove the eight-year-old "NEEDSWORK" comment and formally document this intentional design trade-off.
Signed-off-by: Tian Yuchen <cat@malon.dev> --- patch-ids.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/patch-ids.c b/patch-ids.c index a5683b462c..35e6a974f1 100644 --- a/patch-ids.c +++ b/patch-ids.c @@ -41,7 +41,15 @@ static int patch_id_neq(const void *cmpfn_data, const struct hashmap_entry *entry_or_key, const void *keydata UNUSED) { - /* NEEDSWORK: const correctness? */ + /* + * We drop the 'const' modifier here intentionally. + * + * The hashmap API requires us to treat the entries as const. + * However, to avoid performance regression, we lazily compute + * the patch IDs inside this comparison function. This fundamentally + * requires us to mutate the 'struct patch_id'. Therefore, we use + * container_of() to cast away the constness from the hashmap_entry. + */ struct diff_options *opt = (void *)cmpfn_data; struct patch_id *a, *b;
-- 2.43.0