1 Here we describe the update algorithm. This is responsible for
2 refreshing patches against updated versions of their dependencies,
3 for merging different versions of the various braches created by
4 distributed development, and for implementing decisions to add and
5 remove dependencies from patches.
7 Broadly speaking the update proceeds as follows: during the Ranking
8 phase we construct the intended graph of dependencies between patches
9 (which involves select a merge order for the base branch of each
10 patch). Then during the Traversal phase we walk that graph from the
11 bottom up, constructing for each patch by a series of merges and other
12 operations first a new base branch head commit and then a new tip
13 branch head commit. These new head commits are maximums - that is,
14 each has as ancestors all of its branches' sources and indeed all
15 relevant commits in that branch.
17 We have two possible strategies for constructing new base branch
18 heads: we can either Merge (works incrementally even if there the
19 patch has multiple dependencies, but may sometimes not be possible) or
20 we can Regenerate (trivial if there is a single dependency, and is
21 always possible, but may involve the user re-resolving conflicts if
22 there are multiple dependencies).
28 \desclabelstyle{\nextlinelabel}
30 \item[ $\depsreqof{K}$ ]
31 The set of direct dependencies (in the form $\py$)
32 requested in the commit $K$ ($K \in \pn$) for the patch $\p$.
34 \item[ $\pc \hasdirdep \p$ ]
35 The Topbloke commit set $\pc$ has as a direct contributor the
36 commit set $\p$. This is an acyclic relation.
38 \item[ $\p \hasdep \pq$ ]
39 The commit set $\p$ has as direct or indirect contributor the commit
41 Acyclic; the completion of $\hasdirdep$ into a
44 \item[ $\pendsof{\set J}{\p}$ ]
45 Convenience notation for
46 the maximal elements of $\bigcup_{J \in \set J} \pendsof{J}{\p}$
47 (where $\set J$ is some set of commits).
49 \item[ $\pendsof{\set X}{\p} \le T$ ]
50 Convenience notation for
51 $\bigforall_{E \in \pendsof{\set X}{\p}} E \le T$
53 %\item[ $\set E_{\pc}$ ]
54 %$ \bigcup_i \pendsof{S_{\pc,i}}{\pc} $.
55 %All the ends of $\pc$ in the sources.
57 %\item[ $ \tipzc, \tipcc, \tipuc, \tipfc $ ]
58 %The git ref for the Topbloke commit set $\pc$: respectively,
59 %the original, current, updated, and final values.
63 \stdsection{Inputs to the update algorithm}
67 \desclabelstyle{\nextlinelabel}
70 The topmost patch which we are trying to update. This and
71 all of its dependencies will be updated.
73 \item[ $h : \pc^{+/-} \mapsto \set H_{\pc^{+/-}}$ ]
74 Function for getting the existing heads $\set H$ of the branch $\pc^{+/-}$.
75 This will include the current local and remote git refs, as desired.
77 \item[ $g : \pc, \Gamma \mapsto \Gamma'$ ]
78 Function to allow explicit adjustment of the direct dependencies
79 of $\pc$. It is provided with a putative set of direct dependencies
80 $\Gamma$ computed as an appropriate merge of the dependencies requested by the
81 sources and should return the complete actual set $\Gamma'$ of direct
82 dependencies to use. This allows the specification of any desired
83 (acyclic) relation $\hasdirdep$.
87 \section{Ranking phase}
89 We start with $\allpatches = \{ \}$. We repeat
90 {\bf Rank-Recurse}($\pc_0$) until $\allpatches$ is unchanged.
92 {\bf Rank-Recurse}($\pc$) is:
98 \section{Planning phase}
100 The results of the planning phase consist of:
102 \item{ The relation $\hasdirdep$ and hence the partial order $\hasdep$. }
103 \item{ For each commit set $\pc$, a confirmed set of sources $\set S_{\pc}$. }
104 \item{ For each commit set $\pc$, the order in which to merge the sources
105 $E_{\pc,j} \in \set E_{\pc}$. }
106 \item{ For each $E_{\pc,j}$ an intended merge base $M_{\pc,j}$. }
109 We use a recursive planning algorith, recursing over Topbloke commit
110 sets (ie, sets $\py$ or $\pn$). We'll call the commit set we're
111 processing at each step $\pc$.
112 At each recursive step
113 we make a plan to merge all $\set E_{\pc} = \{ E_{\pc,j \ldots} \}$
114 and all the direct contributors of $\pc$ (as determined below)
115 into $\tipzc$, to make $\tipfc$.
117 We start with $\pc = \pl$ where $\pl = \patchof{L}$.
120 \subsection{Direct contributors for $\pc = \pcn$}
122 The direct contributors of $\pcn$ are the commit sets corresponding to
123 the tip branches for the direct dependencies of the patch $\pc$. We
124 need to calculate what the direct dependencies are going to be.
126 Choose an (arbitrary, but ideally somehow optimal in
127 a way not discussed here) ordering of $\set E_{\pc}$, $E_{\pc,j}$
129 For brevity we will write $E_j$ for $E_{\pc,j}$.
130 Remove from that set (and ordering) any $E_j$ which
131 are $\le$ and $\neq$ some other $E_k$.
133 Initially let $\set D_0 = \depsreqof{\tipzc}$.
134 For each $E_j$ starting with $j=1$ choose a corresponding intended
135 merge base $M_j$ such that $M_j \le E_j \land M_j \le T_{\pc,j-1}$.
136 Calculate $\set D_j$ as the 3-way merge of the sets $\set D_{j-1}$ and
137 $\depsreqof{E_j}$ using as a base $\depsreqof{M_j}$. This will
138 generate $D_m$ as the putative direct contributors of $\pcn$.
140 However, the invocation may give instructions that certain direct
141 dependencies are definitely to be included, or excluded. As a result
142 the set of actual direct contributors is some arbitrary set of patches
143 (strictly, some arbitrary set of Topbloke tip commit sets).
145 \subsection{Direct contributors for $\pc = \pcy$}
147 The sole direct contributor of $\pcy$ is $\pcn$.
149 \subsection{Recursive step}
151 For each direct contributor $\p$, we add the edge $\pc \hasdirdep \p$
152 and augment the ordering $\hasdep$ accordingly.
154 If this would make a cycle in $\hasdep$, we abort . The operation must
155 then be retried by the user, if desired, but with different or
156 additional instructions for modifying the direct contributors of some
157 $\pqn$ involved in the cycle.
159 For each such $\p$, after updating $\hasdep$, we recursively make a plan
164 \section{Execution phase}
166 We process commit sets from the bottom up according to the relation
167 $\hasdep$. For each commit set $\pc$ we construct $\tipfc$ from
168 $\tipzc$, as planned. By construction, $\hasdep$ has $\patchof{L}$
169 as its maximum, so this operation will finish by updating
170 $\tipca{\patchof{L}}$ with $\tipfa{\patchof{L}}$.
172 After we are done with each commit set $\pc$, the
173 new tip $\tipfc$ has the following properties:
174 \[ \eqn{Tip Sources}{
175 \bigforall_{E_i \in \set E_{\pc}} \tipfc \ge E_i
177 \[ \eqn{Tip Dependencies}{
178 \bigforall_{\pc \hasdep \p} \tipfc \ge \tipfa \p
180 \[ \eqn{Perfect Contents}{
181 \tipfc \haspatch \p \equiv \pc \hasdep \py
184 For brevity we will sometimes write $\tipu$ for $\tipuc$, etc. We will start
185 out with $\tipc = \tipz$, and at each step of the way construct some
186 $\tipu$ from $\tipc$. The final $\tipu$ becomes $\tipf$.
188 \subsection{Preparation}
190 Firstly, we will check each $E_i$ for being $\ge \tipc$. If
191 it is, are we fast forward to $E_i$
192 --- formally, $\tipu = \text{max}(\tipc, E_i)$ ---
193 and drop $E_i$ from the planned ordering.
195 Then we will merge the direct contributors and the sources' ends.
196 This generates more commits $\tipuc \in \pc$, but none in any other
197 commit set. We maintain
199 \bigforall_{\p \isdep \pc}
200 \pancsof{\tipcc}{\p} \subset
201 \pancsof{\tipfa \p}{\p}
204 For $\tipcc = \tipzc$, $T$ ...WRONG WE NEED $\tipfa \p$ TO BE IN $\set E$ SOMEHOW
207 \subsection{Merge Contributors for $\pcy$}
209 Merge $\pcn$ into $\tipc$. That is, merge with
210 $L = \tipc, R = \tipfa{\pcn}, M = \baseof{\tipc}$.
211 to construct $\tipu$.
215 Ingredients satisfied by construction.
216 Tip Merge satisfied by construction. Merge Acyclic follows
217 from Perfect Contents and $\hasdep$ being acyclic.
219 Removal Merge Ends: For $\p = \pc$, $M \nothaspatch \p$; OK.
220 For $\p \neq \pc$, by Tip Contents,
221 $M \haspatch \p \equiv L \haspatch \p$, so we need only
222 worry about $X = R, Y = L$; ie $L \haspatch \p$,
223 $M = \baseof{L} \haspatch \p$.
224 By Tip Contents for $L$, $D \le L \equiv D \le M$. OK.~~$\qed$
228 Addition Merge Ends: If $\py \isdep \pcn$, we have already
229 done the execution phase for $\pcn$ and $\py$. By
230 Perfect Contents for $\pcn$, $\tipfa \pcn \haspatch \p$ i.e.
231 $R \haspatch \p$. So we only need to worry about $Y = R = \tipfa \pcn$.
232 By Tip Dependencies $\tipfa \pcn \ge \tipfa \py$.
233 And by Tip Sources $\tipfa \py \ge $
235 want to prove $E \le \tipfc$ where $E \in \pendsof{\tipcc}{\py}$
237 $\pancsof{\tipcc}{\py} = $
240 computed $\tipfa \py$, and by Perfect Contents for $\py$
243 with $M=M_j, L=T_{\pc,j-1}, R=E_j$,
244 and calculate what the resulting desired direct dependencies file
245 (ie, the set of patches $\set D_j$)
246 would be. Eventually we
248 So, formally, we select somehow an order of sources $S_i$. For each
251 Make use of the following recursive algorithm, Plan
256 recursively make a plan to merge all $E = \pends$