From 4deb3898941f51544d43bfef7345114b161e64cc Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Thu, 11 Jun 2026 15:27:13 +0200 Subject: [PATCH] builtin/history: implement "drop" subcommand A common operation when editing the commit history is to drop a specific commit from the history entirely, but this operation is not currently covered by git-history(1). A couple of noteworthy bits: - This is the first git-history(1) command that will ultimately result in changes to both the index and the working tree. We thus have to add logic to merge resulting changes into those. - It is still not possible to replay merge commits, so this limitation is inherited for the new "drop" command. - For now we refuse to drop root commits. While we _can_ indeed drop root commits in the general case, there are edge cases where the resulting history would become completely empty. This is thus left to a subsequent patch series. Other than that, most of the logic is rather straight-forward as we can continue to build on the preexisting logic in git-history(1) for most of the part. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- Documentation/git-history.adoc | 38 ++- builtin/history.c | 186 ++++++++++++ t/meson.build | 1 + t/t3454-history-drop.sh | 537 +++++++++++++++++++++++++++++++++ 4 files changed, 761 insertions(+), 1 deletion(-) create mode 100755 t/t3454-history-drop.sh diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc index 2ba8121795..28b477cd37 100644 --- a/Documentation/git-history.adoc +++ b/Documentation/git-history.adoc @@ -8,6 +8,7 @@ git-history - EXPERIMENTAL: Rewrite history SYNOPSIS -------- [synopsis] +git history drop [--dry-run] [--update-refs=(branches|head)] [--empty=(drop|keep|abort)] git history fixup [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)] git history reword [--dry-run] [--update-refs=(branches|head)] git history split [--dry-run] [--update-refs=(branches|head)] [--] [...] @@ -51,13 +52,28 @@ be stateful operations. The limitation can be lifted once (if) Git learns about first-class conflicts. When using `fixup` with `--empty=drop`, dropping the root commit is not yet -supported. +supported. Likewise, `drop` cannot remove the root commit or a merge commit. COMMANDS -------- The following commands are available to rewrite history in different ways: +`drop `:: + Remove the specified commit from the history. All descendants of the + commit are replayed directly onto its parent. ++ +The root commit cannot be dropped as that may lead to edge cases where refs +end up with no commits anymore. Merge commits cannot be dropped either; see +LIMITATIONS. ++ +If `HEAD` points at a commit that is to be rewritten, the index and working +tree are updated to match the new `HEAD`. The command aborts before any +references are updated in case local modifications would be overwritten. ++ +If replaying any descendant would result in a conflict, the command aborts +with an error. + `fixup `:: Apply the currently staged changes to the specified commit. This is similar in nature to `git commit --fixup=` followed by `git @@ -170,6 +186,26 @@ The staged addition of `unrelated.txt` has been incorporated into the `first` commit. All descendant commits have been replayed on top of the rewritten history. +Drop a commit +~~~~~~~~~~~~~ + +---------- +$ git log --oneline +abc1234 (HEAD -> main) third +def5678 second +ghi9012 first + +$ git history drop 'main^{/second}' + +$ git log --oneline +jkl3456 (HEAD -> main) third +ghi9012 first +---------- + +The `second` commit has been removed from the history, and `third` has been +replayed directly on top of `first`. All branches that pointed at the dropped +commit have been moved to its parent. + Split a commit ~~~~~~~~~~~~~~ diff --git a/builtin/history.c b/builtin/history.c index 4fadf38c32..e59f69233b 100644 --- a/builtin/history.c +++ b/builtin/history.c @@ -17,13 +17,17 @@ #include "read-cache.h" #include "refs.h" #include "replay.h" +#include "reset.h" #include "revision.h" #include "sequencer.h" #include "strvec.h" #include "tree.h" +#include "tree-walk.h" #include "unpack-trees.h" #include "wt-status.h" +#define GIT_HISTORY_DROP_USAGE \ + N_("git history drop [--dry-run] [--update-refs=(branches|head)] [--empty=(drop|keep|abort)]") #define GIT_HISTORY_FIXUP_USAGE \ N_("git history fixup [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]") #define GIT_HISTORY_REWORD_USAGE \ @@ -1001,12 +1005,193 @@ out: return ret; } +static int update_worktree(struct repository *repo, + const struct commit *old_head, + const struct commit *new_head, + bool dry_run) +{ + struct reset_working_tree_options opts = { + .oid_from = &old_head->object.oid, + .oid = &new_head->object.oid, + }; + if (dry_run) + opts.flags |= RESET_WORKING_TREE_DRY_RUN; + return reset_working_tree(repo, &opts); +} + +static int find_head_tree_change(struct repository *repo, + const struct replay_result *result, + struct commit **old_head, + struct commit **new_head, + bool *changed) +{ + const struct replay_ref_update *head_update = NULL; + struct commit *old_head_commit, *new_head_commit; + struct tree *old_head_tree, *new_head_tree; + const char *head_target; + int head_flags; + + *changed = false; + + head_target = refs_resolve_ref_unsafe(get_main_ref_store(repo), + "HEAD", RESOLVE_REF_NO_RECURSE, + NULL, &head_flags); + if (!head_target) + return error(_("cannot look up HEAD")); + if (!(head_flags & REF_ISSYMREF)) + head_target = "HEAD"; + + for (size_t i = 0; i < result->updates_nr; i++) { + if (!strcmp(result->updates[i].refname, head_target)) { + head_update = &result->updates[i]; + break; + } + } + + if (!head_update) + return 0; + + old_head_commit = lookup_commit_reference(repo, &head_update->old_oid); + new_head_commit = lookup_commit_reference(repo, &head_update->new_oid); + if (!old_head_commit || !new_head_commit) + return error(_("cannot resolve HEAD commit")); + + old_head_tree = repo_get_commit_tree(repo, old_head_commit); + new_head_tree = repo_get_commit_tree(repo, new_head_commit); + if (!old_head_tree || !new_head_tree) + return error(_("cannot resolve tree for HEAD")); + + if (oideq(&old_head_tree->object.oid, &new_head_tree->object.oid)) + return 0; + + *old_head = old_head_commit; + *new_head = new_head_commit; + *changed = true; + + return 0; +} + +static int cmd_history_drop(int argc, + const char **argv, + const char *prefix, + struct repository *repo) +{ + const char * const usage[] = { + GIT_HISTORY_DROP_USAGE, + NULL, + }; + enum replay_empty_commit_action empty = REPLAY_EMPTY_COMMIT_DROP; + enum ref_action action = REF_ACTION_DEFAULT; + int dry_run = 0; + struct option options[] = { + OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)", + N_("control which refs should be updated"), + PARSE_OPT_NONEG, parse_ref_action), + OPT_BOOL('n', "dry-run", &dry_run, + N_("perform a dry-run without updating any refs")), + OPT_CALLBACK_F(0, "empty", &empty, "(drop|keep|abort)", + N_("how to handle descendants that become empty"), + PARSE_OPT_NONEG, parse_opt_empty), + OPT_END(), + }; + struct strbuf reflog_msg = STRBUF_INIT; + struct commit *original, *rewritten; + struct rev_info revs = { 0 }; + struct replay_result result = { 0 }; + struct commit *old_head, *new_head; + bool head_moves = false; + int ret; + + argc = parse_options(argc, argv, prefix, options, usage, 0); + if (argc != 1) { + ret = error(_("command expects a single revision")); + goto out; + } + repo_config(repo, git_default_config, NULL); + + if (action == REF_ACTION_DEFAULT) + action = REF_ACTION_BRANCHES; + + original = lookup_commit_reference_by_name(argv[0]); + if (!original) { + ret = error(_("commit cannot be found: %s"), argv[0]); + goto out; + } + + if (!original->parents) { + ret = error(_("cannot drop root commit %s: " + "it has no parent to replay onto"), + argv[0]); + goto out; + } else if (original->parents->next) { + ret = error(_("cannot drop merge commit: %s"), argv[0]); + goto out; + } + + ret = setup_revwalk(repo, action, original, &revs); + if (ret) + goto out; + + rewritten = original->parents->item; + + ret = compute_pending_ref_updates(&revs, action, original, rewritten, + empty, &result); + if (ret) { + ret = error(_("failed replaying descendants")); + goto out; + } + + /* + * If HEAD will move as a result of the rewrite then we'll have to + * merge in the changes into the worktree and index. This merge can of + * course conflict, which will cause the whole operation to abort. + * + * If we had already updated the refs at that point then we'd have an + * inconsistent repository state. So we first perform a dry-run merge + * here before updating refs. + */ + if (!is_bare_repository()) { + ret = find_head_tree_change(repo, &result, &old_head, + &new_head, &head_moves); + if (ret < 0) + goto out; + + if (head_moves && update_worktree(repo, old_head, new_head, true) < 0) { + ret = error(_("dropping this commit would " + "overwrite local changes; aborting")); + goto out; + } + } + + strbuf_addf(&reflog_msg, "drop: dropping %s", argv[0]); + ret = apply_pending_ref_updates(repo, &result, reflog_msg.buf, dry_run); + if (ret < 0) { + ret = error(_("failed to update references")); + goto out; + } + + if (!dry_run && head_moves && update_worktree(repo, old_head, new_head, false) < 0) { + ret = error(_("could not update working tree to new commit %s"), + oid_to_hex(&new_head->object.oid)); + goto out; + } + + ret = 0; + +out: + replay_result_release(&result); + strbuf_release(&reflog_msg); + release_revisions(&revs); + return ret; +} + int cmd_history(int argc, const char **argv, const char *prefix, struct repository *repo) { const char * const usage[] = { + GIT_HISTORY_DROP_USAGE, GIT_HISTORY_FIXUP_USAGE, GIT_HISTORY_REWORD_USAGE, GIT_HISTORY_SPLIT_USAGE, @@ -1014,6 +1199,7 @@ int cmd_history(int argc, }; parse_opt_subcommand_fn *fn = NULL; struct option options[] = { + OPT_SUBCOMMAND("drop", &fn, cmd_history_drop), OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup), OPT_SUBCOMMAND("reword", &fn, cmd_history_reword), OPT_SUBCOMMAND("split", &fn, cmd_history_split), diff --git a/t/meson.build b/t/meson.build index 2af8d01279..d5e71056b2 100644 --- a/t/meson.build +++ b/t/meson.build @@ -399,6 +399,7 @@ integration_tests = [ 't3451-history-reword.sh', 't3452-history-split.sh', 't3453-history-fixup.sh', + 't3454-history-drop.sh', 't3500-cherry.sh', 't3501-revert-cherry-pick.sh', 't3502-cherry-pick-merge.sh', diff --git a/t/t3454-history-drop.sh b/t/t3454-history-drop.sh new file mode 100755 index 0000000000..0f33247212 --- /dev/null +++ b/t/t3454-history-drop.sh @@ -0,0 +1,537 @@ +#!/bin/sh + +test_description='tests for git-history drop subcommand' + +. ./test-lib.sh +. "$TEST_DIRECTORY/lib-log-graph.sh" + +expect_graph () { + cat >expect && + lib_test_cmp_graph --format=%s "$@" +} + +expect_log () { + git log --format="%s" "$@" >actual && + cat >expect && + test_cmp expect actual +} + +test_expect_success 'errors on missing commit argument' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit initial && + test_must_fail git history drop 2>err && + test_grep "command expects a single revision" err + ) +' + +test_expect_success 'errors on too many arguments' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit initial && + test_must_fail git history drop HEAD HEAD 2>err && + test_grep "command expects a single revision" err + ) +' + +test_expect_success 'errors on unknown revision' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit initial && + test_must_fail git history drop does-not-exist 2>err && + test_grep "commit cannot be found: does-not-exist" err + ) +' + +test_expect_success 'errors with invalid --empty= value' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit initial && + test_commit second && + test_must_fail git history drop --empty=bogus HEAD 2>err && + test_grep "unrecognized.*--empty.*bogus" err + ) +' + +test_expect_success 'drops a commit in the middle and replays descendants' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit first && + test_commit second && + test_commit third && + + git symbolic-ref HEAD >expect && + git history drop HEAD~ && + git symbolic-ref HEAD >actual && + test_cmp expect actual && + + expect_log <<-\EOF && + third + first + EOF + + test_must_fail git show HEAD:second.t && + test_path_is_missing second.t && + + git reflog >reflog && + test_grep "drop: dropping HEAD~" reflog + ) +' + +test_expect_success 'drops the HEAD commit' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit first && + test_commit second && + + git history drop HEAD && + + expect_log <<-\EOF + first + EOF + ) +' + +test_expect_success 'drops a commit on detached HEAD' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit first && + test_commit second && + test_commit third && + git checkout --detach HEAD && + + git history drop HEAD~ && + + expect_log <<-\EOF + third + first + EOF + ) +' + +# Note: in this case it would actually be fine to drop the root commit, as we +# do have a descendant commit, and no reference points to the root commit +# directly. So this is something that we may relax eventually. +test_expect_success 'refuses to drop the root commit' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit first && + test_commit second && + + test_must_fail git history drop HEAD~ 2>err && + test_grep "cannot drop root commit" err + ) +' + +# In contrast to the above case, we actually don't want to drop the root commit +# here as that would cause us to end up with an empty commit graph. +test_expect_success 'refuses to drop the root commit when branch becomes empty' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit first && + + test_must_fail git history drop HEAD 2>err && + test_grep "cannot drop root commit" err + ) +' + +test_expect_success 'refuses to drop a merge commit' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit base && + git branch branch && + test_commit ours && + git switch branch && + test_commit theirs && + git switch - && + git merge theirs && + + test_must_fail git history drop HEAD 2>err && + test_grep "cannot drop merge commit" err + ) +' + +test_expect_success 'refuses when descendants contain a merge commit' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit base && + test_commit middle && + git branch branch && + test_commit ours && + git switch branch && + test_commit theirs && + git switch - && + git merge theirs && + + test_must_fail git history drop middle 2>err && + test_grep "replaying merge commits is not supported yet" err + ) +' + +test_expect_success 'works in a bare repository' ' + test_when_finished "rm -rf repo repo.git" && + + git init repo && + test_commit -C repo first && + test_commit -C repo second && + test_commit -C repo third && + + git clone --bare repo repo.git && + ( + cd repo.git && + + git history drop HEAD~ && + expect_log <<-\EOF + third + first + EOF + ) +' + +test_expect_success 'updates branches on other lines of descent' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit base && + test_commit target && + git branch theirs && + test_commit ours && + git switch theirs && + test_commit theirs && + + expect_graph --branches <<-\EOF && + * theirs + | * ours + |/ + * target + * base + EOF + + git history drop target && + + expect_graph --branches <<-\EOF + * ours + | * theirs + |/ + * base + EOF + ) +' + +test_expect_success 'moves branch pointing at dropped commit to its parent' ' + test_when_finished "rm -rf repo" && + git init repo --initial-branch=main && + ( + cd repo && + test_commit first && + test_commit second && + git branch points-at-second && + test_commit third && + + git rev-parse first >expect && + git history drop second && + git rev-parse points-at-second >actual && + test_cmp expect actual && + + expect_log --format="%s %D" --branches <<-\EOF + third HEAD -> main + first tag: first, points-at-second + EOF + ) +' + +test_expect_success '--dry-run prints ref updates without modifying repo' ' + test_when_finished "rm -rf repo" && + git init repo --initial-branch=main && + ( + cd repo && + test_commit base && + git branch branch && + test_commit middle && + test_commit ours && + git switch branch && + test_commit theirs && + + git refs list >refs-expect && + git history drop --dry-run main~ >updates && + git refs list >refs-actual && + test_cmp refs-expect refs-actual && + test_grep "update refs/heads/main" updates && + + git update-ref --stdin modify-me && + + git refs list >refs-expect && + git diff >diff-expect && + test_must_fail git history drop --dry-run HEAD 2>err && + test_grep "dropping this commit would overwrite local changes" err && + git diff >diff-actual && + git refs list >refs-actual && + + test_cmp diff-expect diff-actual && + test_cmp refs-expect refs-actual + ) +' + +test_expect_success '--update-refs=head updates only HEAD' ' + test_when_finished "rm -rf repo" && + git init repo --initial-branch=main && + ( + cd repo && + test_commit base && + test_commit target && + git branch theirs && + test_commit ours && + git switch theirs && + test_commit theirs && + + # When told to update HEAD only, the command refuses to + # rewrite commits that are not an ancestor of HEAD. + test_must_fail git history drop --update-refs=head main 2>err && + test_grep "rewritten commit must be an ancestor of HEAD" err && + + expect_graph --branches <<-\EOF && + * theirs + | * ours + |/ + * target + * base + EOF + + git switch main && + git history drop --update-refs=head target && + + expect_graph --branches <<-\EOF + * ours + | * theirs + | * target + |/ + * base + EOF + ) +' + +test_expect_success 'conflict with replayed commit aborts cleanly' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit base && + test_commit conflict-a file && + test_commit conflict-b file && + + git refs list >refs-expect && + test_must_fail git history drop HEAD~ 2>err && + test_grep "failed replaying descendants" err && + git refs list >refs-actual && + test_cmp refs-expect refs-actual + ) +' + +# Build a history where a descendant of the drop target reverts the change +# introduced by the drop target. After dropping, the descendant's diff applies +# against a tree that already lacks the change, so it becomes empty. +setup_empty_descendant_repo () { + git init "$1" && + ( + cd "$1" && + echo C1 >file && + git add file && + git commit -m "base" && + git tag base && + echo C2 >file && + git add file && + git commit -m "drop-me" && + git tag drop-me && + test_commit middle && + echo C1 >file && + git add file && + git commit -m "revert-drop-me" && + git tag revert-drop-me + ) +} + +test_expect_success '--empty=drop drops descendants that become empty' ' + test_when_finished "rm -rf repo" && + setup_empty_descendant_repo repo && + ( + cd repo && + + git history drop --empty=drop drop-me && + + expect_log <<-\EOF + middle + base + EOF + ) +' + +test_expect_success '--empty=keep keeps descendants that become empty' ' + test_when_finished "rm -rf repo" && + setup_empty_descendant_repo repo && + ( + cd repo && + + git history drop --empty=keep drop-me && + + expect_log <<-\EOF && + revert-drop-me + middle + base + EOF + git diff HEAD~ HEAD >diff && + test_must_be_empty diff + ) +' + +test_expect_success '--empty=abort errors out when a descendant becomes empty' ' + test_when_finished "rm -rf repo" && + setup_empty_descendant_repo repo && + ( + cd repo && + + test_must_fail git history drop --empty=abort drop-me 2>err && + test_grep "became empty after replay" err + ) +' + +test_expect_success 'updates index and worktree when HEAD moves' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit first && + test_commit second && + test_commit third && + + git history drop second && + + # Worktree should no longer contain second.t. + test_path_is_missing second.t && + test_path_is_file first.t && + test_path_is_file third.t && + + # Index and worktree should both match the new HEAD. + git status --porcelain --untracked-files=no >status && + test_must_be_empty status + ) +' + +test_expect_success 'updates worktree when dropping HEAD itself' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit first && + test_commit second && + + git history drop HEAD && + + test_path_is_missing second.t && + test_path_is_file first.t && + + git status --porcelain --untracked-files=no >status && + test_must_be_empty status + ) +' + +test_expect_success 'preserves unrelated unstaged modifications' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit first && + echo first-content >unrelated.txt && + git add unrelated.txt && + git commit -m "add unrelated" && + test_commit second && + test_commit third && + + echo locally-modified >unrelated.txt && + + git diff >diff-expect && + git history drop second && + git diff >diff-actual && + test_cmp diff-expect diff-actual && + test_path_is_missing second.t + ) +' + +test_expect_success 'preserves unrelated staged changes' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit first && + echo first-content >unrelated.txt && + git add unrelated.txt && + git commit -m "add unrelated" && + test_commit second && + test_commit third && + + echo staged-change >unrelated.txt && + git add unrelated.txt && + + git diff --cached >diff-expect && + git history drop second && + git diff --cached >diff-actual && + test_cmp diff-expect diff-actual && + test_path_is_missing second.t + ) +' + +test_expect_success 'aborts when local modifications would be overwritten' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + test_commit base && + test_commit conflict && + + echo local-edit >conflict.t && + git diff >diff-expect && + test_must_fail git history drop HEAD 2>err && + test_grep "would overwrite local changes" err && + git diff >diff-actual && + test_cmp diff-expect diff-actual + ) +' + +test_done