path: root/patch-ids.h
AgeCommit message (Collapse)Author
2021-01-12patch-ids: handle duplicate hashmap entriesJeff King
This fixes a bug introduced in dfb7a1b4d0 (patch-ids: stop using a hand-rolled hashmap implementation, 2016-07-29) in which git rev-list --cherry-pick A...B will fail to suppress commits reachable from A even if a commit with matching patch-id appears in B. Around the time of that commit, the algorithm for "--cherry-pick" looked something like this: 0. Traverse all of the commits, marking them as being on the left or right side of the symmetric difference. 1. Iterate over the left-hand commits, inserting a patch-id struct for each into a hashmap, and pointing commit->util to the patch-id struct. 2. Iterate over the right-hand commits, checking which are present in the hashmap. If so, we exclude the commit from the output _and_ we mark the patch-id as "seen". 3. Iterate again over the left-hand commits, checking whether commit->util->seen is set; if so, exclude them from the output. At the end, we'll have eliminated commits from both sides that have a matching patch-id on the other side. But there's a subtle assumption here: for any given patch-id, we must have exactly one struct representing it. If two commits from A both have the same patch-id and we allow duplicates in the hashmap, then we run into a problem: a. In step 1, we insert two patch-id structs into the hashmap. b. In step 2, our lookups will find only one of these structs, so only one "seen" flag is marked. c. In step 3, one of the commits in A will have its commit->util->seen set, but the other will not. We'll erroneously output the latter. Prior to dfb7a1b4d0, our hashmap did not allow duplicates. Afterwards, it used hashmap_add(), which explicitly does allow duplicates. At that point, the solution would have been easy: when we are about to add a duplicate, skip doing so and return the existing entry which matches. But it gets more complicated. In 683f17ec44 (patch-ids: replace the seen indicator with a commit pointer, 2016-07-29), our step 3 goes away entirely. Instead, in step 2, when the right-hand side finds a matching patch_id from the left-hand side, we can directly mark the left-hand patch_id->commit to be omitted. Solving that would be easy, too; there's a one-to-many relationship of patch-ids to commits, so we just need to keep a list. But there's more. Commit b3dfeebb92 (rebase: avoid computing unnecessary patch IDs, 2016-07-29) built on that by lazily computing the full patch-ids. So we don't even know when adding to the hashmap whether two commits truly have the same id. We'd have to tentatively assign them a list, and then possibly split them apart (possibly into N new structs) at the moment we compute the real patch-ids. This could work, but it's complicated and error-prone. Instead, let's accept that we may store duplicates, and teach the lookup side to be more clever. Rather than asking for a single matching patch-id, it will need to iterate over all matching patch-ids. This does mean examining every entry in a single hash bucket, but the worst-case for a hash lookup was already doing that. We'll keep the hashmap details out of the caller by providing a simple iteration interface. We can retain the simple has_commit_patch_id() interface for the other callers, but we'll simplify its return value into an integer, rather than returning the patch_id struct. That way they won't be tempted to look at the "commit" field of the return value without iterating. Reported-by: Arnaud Morin <> Signed-off-by: Jeff King <> Signed-off-by: Junio C Hamano <>
2019-05-08format-patch: make --base patch-id output stableStephen Boyd
We weren't flushing the context each time we processed a hunk in the patch-id generation code in diff.c, but we were doing that when we generated "stable" patch-ids with the 'patch-id' tool. Let's port that similar logic over from patch-id.c into diff.c so we can get the same hash when we're generating patch-ids for 'format-patch --base=' types of command invocations. Cc: Xiaolong Ye <> Signed-off-by: Stephen Boyd <> Signed-off-by: Junio C Hamano <>
2018-09-21patch-ids.c: remove implicit dependency on the_indexNguyễn Thái Ngọc Duy
Signed-off-by: Nguyễn Thái Ngọc Duy <> Signed-off-by: Junio C Hamano <>
2018-08-15Add missing includes and forward declarationsElijah Newren
I looped over the toplevel header files, creating a temporary two-line C program for each consisting of #include "git-compat-util.h" #include $HEADER This patch is the result of manually fixing errors in compiling those tiny programs. Signed-off-by: Elijah Newren <> Signed-off-by: Junio C Hamano <>
2017-06-02patch-ids: convert to struct object_idBrandon Williams
Signed-off-by: Brandon Williams <> Signed-off-by: Junio C Hamano <>
2017-03-27Convert GIT_SHA1_RAWSZ used for allocation to GIT_MAX_RAWSZbrian m. carlson
Since we will likely be introducing a new hash function at some point, and that hash function might be longer than 20 bytes, use the constant GIT_MAX_RAWSZ, which is designed to be suitable for allocations, instead of GIT_SHA1_RAWSZ. This will ease the transition down the line by distinguishing between places where we need to allocate memory suitable for the largest hash from those where we need to handle the current hash. Signed-off-by: brian m. carlson <> Signed-off-by: Junio C Hamano <>
2016-08-11rebase: avoid computing unnecessary patch IDsKevin Willford
The `rebase` family of Git commands avoid applying patches that were already integrated upstream. They do that by using the revision walking option that computes the patch IDs of the two sides of the rebase (local-only patches vs upstream-only ones) and skipping those local patches whose patch ID matches one of the upstream ones. In many cases, this causes unnecessary churn, as already the set of paths touched by a given commit would suffice to determine that an upstream patch has no local equivalent. This hurts performance in particular when there are a lot of upstream patches, and/or large ones. Therefore, let's introduce the concept of a "diff-header-only" patch ID, compare those first, and only evaluate the "full" patch ID lazily. Please note that in contrast to the "full" patch IDs, those "diff-header-only" patch IDs are prone to collide with one another, as adjacent commits frequently touch the very same files. Hence we now have to be careful to allow multiple hash entries with the same hash. We accomplish that by using the hashmap_add() function that does not even test for hash collisions. This also allows us to evaluate the full patch ID lazily, i.e. only when we found commits with matching diff-header-only patch IDs. We add a performance test that demonstrates ~1-6% improvement. In practice this will depend on various factors such as how many upstream changes and how big those changes are along with whether file system caches are cold or warm. As Git's test suite has no way of catching performance regressions, we also add a regression test that verifies that the full patch ID computation is skipped when the diff-header-only computation suffices. Signed-off-by: Kevin Willford <> Signed-off-by: Junio C Hamano <>
2016-07-29patch-ids: replace the seen indicator with a commit pointerKevin Willford
The cherry_pick_list was looping through the original side checking the seen indicator and setting the cherry_flag on the commit. If we save off the commit in the patch_id we can set the cherry_flag on the correct commit when running through the other side when a patch_id match is found. Signed-off-by: Kevin Willford <> Signed-off-by: Junio C Hamano <>
2016-07-29patch-ids: stop using a hand-rolled hashmap implementationKevin Willford
This change will use the hashmap from the hashmap.h to keep track of the patch_ids that have been encountered instead of using an internal implementation. This simplifies the implementation of the patch ids. Signed-off-by: Kevin Willford <> Signed-off-by: Junio C Hamano <>
2016-04-26patch-ids: make commit_patch_id() a public helper functionXiaolong Ye
Make commit_patch_id() available to other builtins. Signed-off-by: Xiaolong Ye <> Signed-off-by: Junio C Hamano <>
2007-04-12Refactor patch-id filtering out of git-cherry and git-format-patch.Junio C Hamano
This implements the patch-id computation and recording library, patch-ids.c, and rewrites the get_patch_ids() function used in cherry and format-patch to use it, so that they do not pollute the object namespace. Earlier code threw non-objects into the in-core object database, and hoped for not getting bitten by SHA-1 collisions. While it may be practically Ok, it still was an ugly hack. Signed-off-by: Junio C Hamano <>