1 Basic update algorithm:
3 1. recurse to all of our direct dependencies and
4 update their bases and tips
8 i. Compute our base's set of desired included deps:
9 The set of desired included deps for a base
10 is the union of the desired included deps for each
11 branch named in the base's branch's direct deps, plus
12 the name of every direct external dep.
13 The set of desired included deps for a branch
14 is the set of desired included deps for the branch's
15 base plus the branch name itself.
17 ii. For each source in the best order, do the following merge:
18 (Our base has sources:
19 - the branch for each direct dep
21 - the topgit base, if this is a topgit import)
23 Find the (latest) common ancestor.
25 Check for unwanted dependency removals.
26 An unwanted dependency removal is
27 A branch in the desired included deps
28 Which exists in the common ancestor's actual included deps
29 but which is missing in the source's actual included deps
30 (NB that this definition excludes dependency removals
31 which have already occurred on our base; these will be
33 For each unwanted dependency removal (ie for each such
34 branch), search as follows:
35 * An "unwanted removal commit" is a non-merge commit in the
36 history of the source, which removes the dep from the
38 * But the search stops at any point where we would have to
39 traverse a commit where .topbloke/deps is empty (which
40 stops us looking into the hitory of non-topbloke-controlled
41 branches). This can be done with git-rev-list
43 * The the relevant unwanted removal commit for that dep is
44 the most recent unwanted removal commit, as defined.
45 Select the unwantedly removed dep whose relevant unwanted
46 removal commit is the earliest. Merge from the ancestor of
47 that relevant unwanted removal commit. Merge from the relevant
48 unwanted removal commit using -s ours.
50 Now continue to the next unwanted dependency removal.
52 (The purpose of this, and the result, is that the unwanted
53 dependency removal has gone away. Doing things in this order
54 tries to keep the unwanted dependency removal's reversions as
55 close as possible to their originating points. The
56 recursion, which processes dependencies before their clients,
57 tries to keep the reversion churn localised: client patches
58 of a patch affected by an unwanted removal will benefit from
59 that client's resolution of the situation.)
61 If there are no (more) unwanted dependency removals, merge
65 Check for missing or unwanted dependency inclusions. Compare
66 our base's desired included deps with our base's actual
67 included deps. In exceptional conditions, they will not
68 be identical. This can happen, for example, because a
69 dependency removal was incorporated into our base branch but
70 the removed branch was introduced as an explicit dependency.
71 This will also happen if we remove a dependency ourselves.
73 Do the unwanted inclusions first, and then the missing ones.
74 (This is because that the missing ones cannot depend on the
75 unwanted ones, as otherwise the unwanted ones would be in the
76 desired inclusions. So removing the unwanted ones first
77 reduces the chances of conflicts.)
80 * Do the comparison between desired and actual included
81 * Pick a missing inclusion, or failing that an unwanted one
82 (call this the "relevant" branch)
83 * Depth first search all of the dependencies of the
84 relevant branch; if any of these is also a missing
85 (resp. unwanted) inclusion, start again processing it
87 * Attempt to apply the appropriate diff to add (resp. remove)
88 the contents of the relevant patch (adjusted appropriately
89 for metadata, XXX??? particularly the actual inclusion list)
90 XXX if we want to add a dep we need to update the dep first
91 * Go round again looking for another discrepancy.
94 Our branch has sources:
96 - the remote for our branch
97 - the topgit branch, if this is a topgit import
98 For each source in the best order, do the merge.
100 Double-check the actual dependency inclusions. In
101 particular, if we just upgraded to actual dependency tracking
102 we may need to explicitly add our branch name to the actual
103 dependency inclusion list.
105 The "best order" for merges is in order of recency of common
106 ancestor, most recent first, and if that does not distinguish,
107 merging from local branches first.
109 "Recency" refers to the order from git-rev-list --date-order.
111 Actual included deps:
113 This is tracked explicitly in .topbloke/included, one branch per
114 line. For compatibility with older versions, every time we think
115 about a base, branch or source above, we check whether
116 .topbloke/included is present.
118 If it isn't then we calculate a child commit which has a
119 .topbloke/included. In the case of a remote branch or base, we
120 substitute this child commit for the relevant remote ref but do
121 not record it in the remote ref; in the case of a local branch or
122 base, we advance the local branch or base accordingly.
124 When .topbloke/included is calculated in this way, it always gets
125 the list of desired included deps. (topgit,
126 which does not support dependency deletion, always has exactly the
127 desired deps actually included.)
129 Foreign branches cannot be removed from included and cannot
130 therefore be removed from dependency lists.
135 - removed patch must be removed from the deps of its
136 ex-children, and replaced with the deps of the removed
139 - removed patch wants not to be in list of patches "tb-list"
141 branches in refs/topbloke-tips ? yes
142 deleted patches do something to the base ? no
144 deleting empty patch: dependencies fine
145 deleting nonempty patch: if any dependencies found, their
149 - remove from views of active patches
150 - prevent new commits
151 - remove from dependencies of active patches
152 only makes sense if no active patches depend on it.
155 - just unmark the patch as deleted
159 When merging from a foreign dependency, check that it
160 does not have .topbloke metadata; LATER if it
161 does, could produce a new commit which has .topbloke removed
165 needs to be globally unique
166 so put email address in it
167 tg operations search for applicable patches
168 safe charset for patch names
170 not permitted (git-check-ref-format(1))
176 When pulling, which remotes get to update which patches ?
177 Complicated question!
179 For now, have "blessed" remotes, which we always pull and update from.
180 All these count as sources above.
182 Update operation restrictions available, which restrict use of various
183 sources above ? What about implications for correctness of merge
187 Concept of a "stack" ?
188 Unnecessary - instead, deal with leaf patches
189 Operations like "go up the stack", goes towards leaf. Hopefully unique.
190 "Down" the stack, uses a "conventional" linearisation
191 Stack reordering op ? auto adjust deps
194 When merging, we need to DTRT with our metadata.
195 Do this by running write-tree/read-tree etc. ourselves ?
196 For a source we're merging from, we make a version where the
197 metadata we shouldn't be merging is removed ?
199 Have discovered that specifying a custom merge driver for a file does
200 not have any effect if the three-way-merge looks trivial based
201 on looking at the file contents - at least, if you use git-merge.
203 Only thing which knows how to do all the gitattributes stuff and
204 conflict markers and what have you is git-merge. (git-merge-tree does
205 too but the output format is unsuitable.) "git-merge-index
206 ... git-merge-one-file" does not honour the merge drivers and is,
207 contrary to what the git docs seem to suggest but don't actually
208 state, not actualy used by git-merge.
210 OK so here is a plan:
211 Use git-merge --no-commit
212 Perhaps on a HEAD, and/or against a tree, which have been massaged
213 to make the metadata suitable as input.
214 Filtering out the "merge was successful but we aren't committing"
215 message. Use a single pipe for stdout/stderr to get interleaving
216 right; the message from git-merge is not i18n'd.
218 Check for merge success in the index and compare to exit status
219 from git-merge (which is 1 if the merge failed).
221 Print appropriate big fat warnings if we have merge conflicts in our
223 Commit, adjusting the parents of the new commit to the original
224 parents if we made the merge with special massaged parents.
225 We may still need to have custom merge drivers for metadata.
228 Strategies for each metadata file merge:
230 in base/tip same patch's tip dep -> base base -> tip
232 msg T textual merge rm from src not in src
233 deps T list merge rm from src not in src
234 deleted T std existence merge rm from src not in src
235 patch- BT must be same rm from src must be same
236 topgit- T must be same rm from src not in src
237 [^+]*- ?? textual merge rm from src rm from src
238 +included BT list merge rm from non-tb src list merge
239 +*- ?? textual merge rm from non-tb src textual merge
240 *[^-] ?? die, aborting all ops, if found in any tb src or branch