Hi Chris
On 23/09/2022 19:55, Stefan Xenos via GitGitGadget wrote:
From: Stefan Xenos <sxenos@xxxxxxxxxx>
metacommit.c supports the creation of metacommits and
adds the API needed to create and update changes.
Create the "modify_change" function that can be called from modification
commands like "rebase" and "git amend" to record obsolescences in the
change graph.
Create the "record_metacommit" function for recording more complicated
commit relationships in the commit graph.
Create the "write_metacommit" function for low-level creation of
metacommits.
The commit message fails to mention that we do not create a
"parent-type" header when we create a metacommit but instead abuse the
commit message.
As with the other patches there are a lot of style comments, but to try
and limit the noise I've only commented on one instance of each - you
should apply the comments to all occurrences in all patches.
I've left a couple of questions where I'm not sure exactly what the code
is trying to do but apart from an easily fixed NULL pointer de-reference
and not actually creating the "parent-type" header it looks pretty good.
I was glad to see that there are no obvious memory leaks. I do think the
patches in this series would be easier to follow if the function
parameter names were nouns rather than verbs.
Signed-off-by: Stefan Xenos <sxenos@xxxxxxxxxx>
Signed-off-by: Chris Poucet <poucet@xxxxxxxxxx>
---
Makefile | 1 +
metacommit.c | 404 +++++++++++++++++++++++++++++++++++++++++++++++++++
metacommit.h | 58 ++++++++
3 files changed, 463 insertions(+)
create mode 100644 metacommit.c
create mode 100644 metacommit.h
diff --git a/Makefile b/Makefile
index 2b847e7e7de..68082ef94c7 100644
--- a/Makefile
+++ b/Makefile
@@ -1000,6 +1000,7 @@ LIB_OBJS += merge-ort.o
LIB_OBJS += merge-ort-wrappers.o
LIB_OBJS += merge-recursive.o
LIB_OBJS += merge.o
+LIB_OBJS += metacommit.o
LIB_OBJS += metacommit-parser.o
I think the code to parse and create metacommits (as well as the change
table code) could quite happily live in the same file.
diff --git a/metacommit.c b/metacommit.c
new file mode 100644
index 00000000000..d2b859a4d3b
--- /dev/null
+++ b/metacommit.c
@@ -0,0 +1,404 @@
+#include "cache.h"
+#include "metacommit.h"
+#include "commit.h"
+#include "change-table.h"
+#include "refs.h"
+
+void init_metacommit_data(struct metacommit_data *state)
+{
+ memset(state, 0, sizeof(*state));
+}
We'd normally use an initializer macro instead
#define METACOMMIT_DATA_INIT = { 0 }
+void clear_metacommit_data(struct metacommit_data *state)
+{
+ oid_array_clear(&state->replace);
+ oid_array_clear(&state->origin);
+}
+
+static void compute_default_change_name(struct commit *initial_commit,
+ struct strbuf* result)
+{
+ struct strbuf default_name;
The canonical way to initialize an strbuf that is not on the heap is
struct strbuf buf = STRBUF_INIT;
+ const char *buffer;
+ const char *subject;
+ const char *eol;
+ int len;
+ strbuf_init(&default_name, 0);
+ buffer = get_commit_buffer(initial_commit, NULL);
+ find_commit_subject(buffer, &subject);
+ eol = strchrnul(subject, '\n');
+ for (len = 0;subject < eol && len < 10; ++subject, ++len) {
There's a space missing after the first ';'. We prefer post-increments
to pre-increments unless the pre-increment is significant.
+ char next = *subject;
+ if (isspace(next))
+ continue;
+
+ strbuf_addch(&default_name, next);
+ }
+ sanitize_refname_component(default_name.buf, result);
I suspect we need to call unuse_commit_buffer(initial_commit) here.
+}
+
+/**
+ * Computes a change name for a change rooted at the given initial commit. Good
+ * change names should be memorable, unique, and easy to type. They are not
+ * required to match the commit comment.
+ */
+static void compute_change_name(struct commit *initial_commit, struct strbuf* result)
+{
+ struct strbuf default_name;
+ struct object_id unused;
+
+ strbuf_init(&default_name, 0);
+ if (initial_commit)
+ compute_default_change_name(initial_commit, &default_name);
+ else
+ strbuf_addstr(&default_name, "change");
What does it mean to call this function with initial_commit == NULL?
+ strbuf_addstr(result, "refs/metas/");
+ strbuf_addbuf(result, &default_name);
+ /* If there is already a change of this name, append a suffix */
+ if (!read_ref(result->buf, &unused)) {
+ int suffix = 2;
+ int original_length = result->len;
This is one of many places where we have a size_t len or nr member and
assign it to an int. I think it would be clearer to use a size_t instead
to avoid adding any more signed<->unsigned conversions.
+
+ while (1) {
+ strbuf_addf(result, "%d", suffix);
+ if (read_ref(result->buf, &unused))
+ break;
+ strbuf_remove(result, original_length, result->len - original_length);
+ ++suffix;
+ }
+ }
+
+ strbuf_release(&default_name);
+}
+
+struct resolve_metacommit_callback_data
While there are some structs with a _callback_data suffix in the code
base, it is far more common to use _context and name any corresponding
variables ctx.
+{
+ struct change_table* active_changes;
+ struct string_list *changes;
+ struct oid_array *heads;
+};
+
+static int resolve_metacommit_callback(const char *refname, void *cb_data)
+{
+ struct resolve_metacommit_callback_data *data = (struct resolve_metacommit_callback_data *)cb_data;
We don't use redundant casts such as this.
+ struct change_head *chhead;
+
+ chhead = get_change_head(data->active_changes, refname);
This is really a comment on the previous patch but are there uses of
for_each_change_referencing() for which just the refname is sufficient?
It might be more convenient to pass the change head into the callback as
well.
+
+ if (data->changes)
+ string_list_append(data->changes, refname)->util = &(chhead->head);
We don't use redundant parentheses such as this (and this patch does not
use them consistently)
+ if (data->heads)
+ oid_array_append(data->heads, &(chhead->head));
+
+ return 0;
+}
+
+/**
+ * Produces the final form of a metacommit based on the current change refs.
+ */
+static void resolve_metacommit(
+ struct repository* repo,
+ struct change_table* active_changes,
+ const struct metacommit_data *to_resolve,
[testing my understanding] This is the metacommit we want to update
+ struct metacommit_data *resolved_output,
This is the updated metacommit returned to the user
+ struct string_list *to_advance,
Is also an output? It ends up as a list of refname to change head mappings
+ int allow_append)
+{
+ int i;
+ int len = to_resolve->replace.nr;
+ struct resolve_metacommit_callback_data cbdata;
This would be a good place to a designated initializer.
struct resolve_metacommit_context ctx = {
.active_changes = active_changes,
.changes = to_advance,
.heads = &resolved_output->replace
};
+ int old_change_list_length = to_advance->nr;
+ struct commit* content;
+
+ oidcpy(&resolved_output->content, &to_resolve->content);
+
+ /* First look for changes that point to any of the replacement edges in the
+ * metacommit. These will be the changes that get advanced by this
+ * metacommit. */
Style: '/*' & '*/' should be on their own lines.
+ resolved_output->abandoned = to_resolve->abandoned;
+ cbdata.active_changes = active_changes;
+ cbdata.changes = to_advance;
+ cbdata.heads = &(resolved_output->replace);
+
+ if (allow_append) {
+ for (i = 0; i < len; i++) {
+ int old_number = resolved_output->replace.nr;
+ for_each_change_referencing(active_changes, &(to_resolve->replace.oid[i]),
+ resolve_metacommit_callback, &cbdata);
+ /* If no changes were found, use the unresolved value. */
+ if (old_number == resolved_output->replace.nr)
+ oid_array_append(&(resolved_output->replace), &(to_resolve->replace.oid[i]));
We see if there are any refs under refs/metas/ which point to
'to_resolve' or its content and if there are we add those refs and the
corresponding change head to 'to_advance'. If we don't find any refs
then we copy the replace oid from 'to_resolve' to 'resolved_output'
If allow_append is false then we ignore all the replace oids in 'to_resolve'
+ }
+ }
+
+ cbdata.changes = NULL;
+ cbdata.heads = &(resolved_output->origin);
+
+ len = to_resolve->origin.nr;
+ for (i = 0; i < len; i++) {
+ int old_number = resolved_output->origin.nr;
+ for_each_change_referencing(active_changes, &(to_resolve->origin.oid[i]),
+ resolve_metacommit_callback, &cbdata);
+ if (old_number == resolved_output->origin.nr)
+ oid_array_append(&(resolved_output->origin), &(to_resolve->origin.oid[i]));
+ }
This is copying the origin oids in the same way as we copied the replace
oids above.
+ /* If no changes were advanced by this metacommit, we'll need to create a new
+ * one. */
+ if (to_advance->nr == old_change_list_length) {
+ struct strbuf change_name;
+
+ strbuf_init(&change_name, 80);
+ content = lookup_commit_reference_gently(repo, &(to_resolve->content), 1);
+
+ compute_change_name(content, &change_name);
+ string_list_append(to_advance, change_name.buf);
+ strbuf_release(&change_name);
+ }
+}
+
+static void lookup_commits(
+ struct repository *repo,
+ struct oid_array *to_lookup,
+ struct commit_list **result)
+{
+ int i = to_lookup->nr;
+
+ while (--i >= 0) {
+ struct object_id *next = &(to_lookup->oid[i]);
+ struct commit *commit = lookup_commit_reference_gently(repo, next, 1);
+ commit_list_insert(commit, result);
+ }
We walk backwards because commit_list_insert prepends to the list - good.
+}
+
+#define PARENT_TYPE_PREFIX "parent-type "
+
+/**
+ * Creates a new metacommit object with the given content. Writes the object
+ * id of the newly-created commit to result.
+ */
+int write_metacommit(struct repository *repo, struct metacommit_data *state,
+ struct object_id *result)
+{
+ struct commit_list *parents = NULL;
+ struct strbuf comment;
+ int i;
+ struct commit *content;
+
+ strbuf_init(&comment, strlen(PARENT_TYPE_PREFIX)
+ + 1 + 2 * (state->origin.nr + state->replace.nr));
+ lookup_commits(repo, &state->origin, &parents);
+ lookup_commits(repo, &state->replace, &parents);
+ content = lookup_commit_reference_gently(repo, &state->content, 1);
+ if (!content) {
+ strbuf_release(&comment);
+ free_commit_list(parents);
+ return -1;
+ }
+ commit_list_insert(content, &parents);
+
+ strbuf_addstr(&comment, PARENT_TYPE_PREFIX);
+ strbuf_addstr(&comment, state->abandoned ? "a" : "c");
+ for (i = 0; i < state->replace.nr; i++)
+ strbuf_addstr(&comment, " r");
+
+ for (i = 0; i < state->origin.nr; i++)
+ strbuf_addstr(&comment, " o"); > + /* The parents list will be freed by this call. */
+ commit_tree(comment.buf, comment.len, repo->hash_algo->empty_tree, parents,
+ result, NULL, NULL);
It would be relatively easy to use commit_tree_extended() with
extra_headers so that we create a commit with a "parent-type" header
rather than abusing the commit message.
struct commit_extra_header extra = { .key = "parent-type" };
/* build header value in strbuf */
extra.value = buf.buf;
extra.len = buf.len;
commit_tree_extended("", 0, repo->hash_algo->empty_tree,
parents, result, NULL, NULL, NULL,
&extra);
+
+ strbuf_release(&comment);
+ return 0;
+}
+
+/**
+ * Returns true iff the given metacommit is abandoned, has one or more origin
+ * parents, or has one or more replacement parents.
+ */
+static int is_nontrivial_metacommit(struct metacommit_data *state)
+{
+ return state->replace.nr || state->origin.nr || state->abandoned;
+}
+
+/*
+ * Records the relationships described by the given metacommit in the
+ * repository.
+ *
+ * If override_change is NULL (the default), an attempt will be made
+ * to append to existing changes wherever possible instead of creating new ones.
+ * If override_change is non-null, only the given change ref will be updated.
So override_head is the refname of an existing change?
+ * options is a bitwise combination of the UPDATE_OPTION_* flags.
+ */
+int record_metacommit(
+ struct repository *repo,
+ const struct metacommit_data *metacommit, const char *override_change,
+ int options, struct strbuf *err)
+{
+ struct change_table chtable;
+ struct string_list changes;
+ int result;
+
+ change_table_init(&chtable);
+ change_table_add_all_visible(&chtable, repo);
+ string_list_init_dup(&changes);
+
+ result = record_metacommit_withresult(repo, &chtable, metacommit,
+ override_change, options, err, &changes);
+
+ string_list_clear(&changes, 0);
+ change_table_clear(&chtable);
+ return result;
+}
+
+/*
+ * Records the relationships described by the given metacommit in the
+ * repository.
+ *
+ * If override_change is NULL (the default), an attempt will be made
+ * to append to existing changes wherever possible instead of creating new ones.
+ * If override_change is non-null, only the given change ref will be updated.
+ *
+ * The changes list is filled in with the list of change refs that were updated,
+ * with the util pointers pointing to the old object IDS for those changes.
+ * The object ID pointers all point to objects owned by the change_table and
+ * will go out of scope when the change_table is destroyed.
That potentially sounds like an invitation to create use after free bugs
unless we're careful. Does this function need to be public?
+ *
+ * options is a bitwise combination of the UPDATE_OPTION_* flags.
+ */
+int record_metacommit_withresult(
+ struct repository *repo,
+ struct change_table *chtable,
+ const struct metacommit_data *metacommit,
+ const char *override_change,
+ int options, struct strbuf *err,
+ struct string_list *changes)
+{
+ static const char *msg = "updating change";
+ struct metacommit_data resolved_metacommit;
+ struct object_id commit_target;
+ struct ref_transaction *transaction = NULL;
+ struct change_head *overridden_head;
+ const struct object_id *old_head;
+
+ int i;
+ int ret = 0;
+ int force = (options & UPDATE_OPTION_FORCE);
+
+ init_metacommit_data(&resolved_metacommit);
+
+ resolve_metacommit(repo, chtable, metacommit, &resolved_metacommit, changes,
+ (options & UPDATE_OPTION_NOAPPEND) == 0);
+
+ if (override_change) {
+ string_list_clear(changes, 0);
+ overridden_head = get_change_head(chtable, override_change);
+ if (!overridden_head) {
We enter this branch if overridden_head is NULL
+ /* This is an existing change */
+ old_head = &overridden_head->head;
Here we de-reference overridden_head which is NULL
+ if (!force) {
+ if (!oid_array_readonly_contains(&(resolved_metacommit.replace),
+ &overridden_head->head)) {
+ /* Attempted non-fast-forward change */
+ strbuf_addf(err, _("non-fast-forward update to '%s'"),
+ override_change);
+ ret = -1;
+ goto cleanup;
+ }
+ }
+ } else
Style: if one branch of an if statement requires braces then all
branches should have braces.
+ /* ...then this is a newly-created change */
+ old_head = null_oid();
+
+ /* The expected "current" head of the change is stored in the util
+ * pointer. */
+ string_list_append(changes, override_change)->util = (void*)old_head;
No need to cast here
+ }
+
+ if (is_nontrivial_metacommit(&resolved_metacommit)) {
+ /* If there are any origin or replacement parents, create a new metacommit
+ * object. */
+ if (write_metacommit(repo, &resolved_metacommit, &commit_target) < 0) {
+ ret = -1;
+ goto cleanup;
+ }
+ } else
+ /**
+ * If the metacommit would only contain a content commit, point to the
+ * commit itself rather than creating a trivial metacommit.
+ */
+ oidcpy(&commit_target, &(resolved_metacommit.content));
Oh, is this optimization why we don't insist on metacommits but also
allow ordinary commits to be added to the change table?
diff --git a/metacommit.h b/metacommit.h
new file mode 100644
index 00000000000..fdb253f0f04
--- /dev/null
+++ b/metacommit.h
@@ -0,0 +1,58 @@
+#ifndef METACOMMIT_H
+#define METACOMMIT_H
+
+#include "hash.h"
+#include "oid-array.h"
+#include "repository.h"
+#include "string-list.h"
+
+
+struct change_table;
+
+/* If specified, non-fast-forward changes are permitted. */
+#define UPDATE_OPTION_FORCE 0x0001
+/**
+ * If specified, no attempt will be made to append to existing changes.
+ * Normally, if a metacommit points to a commit in its replace or origin
+ * list and an existing change points to that same commit as its content, the
+ * new metacommit will attempt to append to that same change. This may replace
+ * the commit parent with one or more metacommits from the head of the appended
+ * changes. This option disables this behavior, and will always create a new
+ * change rather than reusing existing changes.
+ */
+#define UPDATE_OPTION_NOAPPEND 0x0002
+
+/* Metacommit Data */
+
+struct metacommit_data {
+ struct object_id content;
+ struct oid_array replace;
+ struct oid_array origin;
+ int abandoned;
+};
+
+extern void init_metacommit_data(struct metacommit_data *state);
+
+extern void clear_metacommit_data(struct metacommit_data *state);
+
+extern int record_metacommit(struct repository *repo,
+ const struct metacommit_data *metacommit,
+ const char* override_change, int options, struct strbuf *err);
+
+extern int record_metacommit_withresult(
+ struct repository *repo,
+ struct change_table *chtable,
+ const struct metacommit_data *metacommit,
+ const char *override_change,
+ int options,
+ struct strbuf *err,
+ struct string_list *changes);
Does this need to be public? i.e. why would one call this rather than
record_metacommit()?
+extern void modify_change(struct repository *repo,
+ const struct object_id *old_commit, const struct object_id *new_commit,
+ struct strbuf *err);
+
+extern int write_metacommit(struct repository *repo, struct metacommit_data *state,
+ struct object_id *result);
The documentation for the flags is very welcome but this header could to
with the api being documented as well.
Best Wishes
Phillip
