-When we are trying to do a merge of some kind, in general,
-we want to merge some source commits $S_0 \ldots S_n$.
-We'll write $S_0 = L$. We require that $L$ is the current git ref
-for $\patchof{L}$.
-
-\stdsection{Notation}
+Here we describe the update algorithm. This is responsible for
+refreshing patches against updated versions of their dependencies,
+for merging different versions of the various braches created by
+distributed development, and for implementing decisions to add and
+remove dependencies from patches.
+
+Broadly speaking the update proceeds as follows: during the Ranking
+phase we construct the intended graph of dependencies between patches
+(and incidentally select a merge order for the base branch of each
+patch). Then during the Traversal phase we walk that graph from the
+bottom up, constructing for each patch by a series of merges and other
+operations first a new base branch head commit and then a new tip
+branch head commit. These new head commits are maximums - that is,
+each has as ancestors all of its branches' sources and indeed all
+relevant commits in that branch.
+
+We have two possible strategies for constructing new base branch
+heads: we can either Merge (works incrementally even if there the
+patch has multiple dependencies, but may sometimes not be possible) or
+we can Regenerate (trivial if there is a single dependency, and is
+always possible, but may involve the user re-resolving conflicts if
+there are multiple dependencies).
+
+\section{Notation}
\begin{basedescript}{
\desclabelwidth{5em}
requested in the commit $K$ ($K \in \pn$) for the patch $\p$.
\item[ $\pc \hasdirdep \p$ ]
-The Topbloke commit set $\pc$ has as a direct contributors the
-commit set $\p$. This is an acyclic relation.
+The patch $\pc$ has as a direct dependency the
+patch $\p$. This is an acyclic relation.
\item[ $\p \hasdep \pq$ ]
-The commit set $\p$ has as direct or indirect contributor the commit
-set $\pq$.
+The patch $\p$ has as direct or indirect dependency the
+patch $\pq$.
Acyclic; the completion of $\hasdirdep$ into a
partial order.
-\item[ $\set E_{\pc}$ ]
-$ \bigcup_i \pendsof{S_i}{\pc} $.
-All the ends of $\pc$ in the sources.
+\item[ $\pendsof{\set J}{\p}$ ]
+Convenience notation for
+the $\le$-maximal elements of $\bigcup_{J \in \set J} \pendsof{J}{\p}$
+(where $\set J$ is some set of commits).
+
+\item[ $\pendsof{\set X}{\p} \le T$ ]
+Convenience notation for
+$\bigforall_{E \in \pendsof{\set X}{\p}} E \le T$
+
+%\item[ $\set E_{\pc}$ ]
+%$ \bigcup_i \pendsof{S_{\pc,i}}{\pc} $.
+%All the ends of $\pc$ in the sources.
-\item[ $ \grefzc, \grefcc, \grefuc, \greffc $ ]
-The git ref for the Topbloke commit set $\pc$: respectively,
-the original, current, updated, and final values.
+%\item[ $ \tipzc, \tipcc, \tipuc, \tipfc $ ]
+%The git ref for the Topbloke commit set $\pc$: respectively,
+%the original, current, updated, and final values.
+
+\end{basedescript}
+
+\stdsection{Inputs to the update algorithm}
+
+\begin{basedescript}{
+\desclabelwidth{5em}
+\desclabelstyle{\nextlinelabel}
+}
+\item[ $\pc_0$ ]
+The topmost patch which we are trying to update. This and
+all of its dependencies will be updated.
+
+\item[ $h : \pc^{+/-} \mapsto \set H_{\pc^{+/-}}$ ]
+Function for getting the existing heads $\set H$ of the branch $\pc^{+/-}$.
+These are the heads which will be merged and used in this update.
+This will include the current local and remote git refs, as desired.
+
+\item[ $g : \pc, \Gamma \mapsto \Gamma'$ ]
+Function to allow explicit adjustment of the direct dependencies
+of $\pc$. It is provided with a putative set of direct dependencies
+$\Gamma$ computed as an appropriate merge of the dependencies requested by the
+sources and should return the complete actual set $\Gamma'$ of direct
+dependencies to use. This allows the specification of any desired
+(acyclic) relations $\hasdirdep$ and $\hasdep$.
\end{basedescript}
-\section{Planning phase}
+\stdsection{Important variables and values in the update algorithm}
+
+\begin{basedescript}{
+\desclabelwidth{5em}
+\desclabelstyle{\nextlinelabel}
+}
+\item[ $\Gamma_{\pc}$ ]
+The desired direct dependencies of $\pc$, a set of patches.
+
+\item[ $\allpatches$ ]
+The set of all the patches we are dealing with (constructed
+during the update algorithm).
+
+\item[ $\tipcn, \tipcy$ ]
+The new tips of the git branches $\pcn$ and $\pcy$, containing
+all the correct commits (and the correct other patches), as
+generated by the Traversal phase of the update algorithm.
+
+\end{basedescript}
+
+\section{Ranking phase}
+
+We run the following algorithm:
+\begin{enumerate}
+\item Set $\allpatches = \{ \}$.
+\item Repeatedly:
+\begin{enumerate}
+\item Clear out the graph $\hasdirdep$ so it has no edges.
+\item Execute $\alg{Rank-Recurse}(\pc_0)$
+\item Until $\allpatches$ remains unchanged.
+\end{enumerate}
+\end{enumerate}
+
+$\alg{Rank-Recurse}(\pc)$ is:
+\begin{enumerate}
+
+\item If we have already done $\alg{Rank-Recurse}(\pc)$ in this
+ranking iteration, do nothing. Otherwise:
+
+\item Add $\pc$ to $\allpatches$ if it is not there already.
+
+\item Set
+$$
+ \set S \iassign h(\pcn)
+ \cup
+ \bigcup_{\p \in \allpatches}
+ \bigcup_{H \in h(\pn) \lor H \in h(\py)}
+ \{ \baseof{E} \; | \; E \in \pendsof{H}{\pcy} \}
+$$
+
+and $W \iassign w(h(\pcn))$
+
+\item While $\exists_{S \in \set S} S \ge W$,
+update $W \assign S$ and $\set S \assign \set S \, \backslash \{ S \}$
+
+(This will often remove $W$ from $\set S$. Afterwards, $\set S$
+is a collection of heads to be merged into $W$.)
+
+\item Choose an ordering of $\set S$, $S_i$ for $i=1 \ldots n$.
+
+\item For each $S_i$ in turn, choose a corresponding $M_i$
+such that $$
+ M_i \le S_i \land \left[
+ M_i \le W \lor \bigexists_{j<i} M_i \le S_j
+ \right]
+$$
+
+\item Set $\Gamma \iassign \depsreqof{W}$.
+
+If there are multiple candidates we prefer $M_i \in \pcn$
+if available.
+
+\item For each $i \ldots 1..n$, update our putative direct
+dependencies:
+$$
+\Gamma \assign \setmergeof{
+ \Gamma
+ }{
+ \begin{cases}
+ M_i \in \pcn : & \depsreqof{M_i} \\
+ M_i \not\in \pcn : & \{ \}
+ \end{cases}
+ }{
+ \depsreqof{S_i}
+ }
+$$
+
+TODO define $\setmerge$
+
+\item Finalise our putative direct dependencies
+$
+\Gamma \assign g(\pc, \Gamma)
+$
+
+\item For each direct dependency $\pd \in \Gamma$,
+
+\begin{enumerate}
+\item Add an edge $\pc \hasdirdep \pd$ to the digraph (adding nodes
+as necessary).
+If this results in a cycle, abort entirely (as the function $g$ is
+inappropriate; a different $g$ could work).
+\item Run $\alg{Rank-Recurse}(\pd)$.
+\end{enumerate}
+
+\end{enumerate}
+
+\subsection{Results of the ranking phase}
+
+By the end of the ranking phase, we have recorded the following
+information:
+
+\begin{itemize}
+\item
+$ \allpatches, \hasdirdep $ and hence the completion of $\hasdirdep$
+into the partial order $\hasdep$.
+
+\item
+For each $\pc \in \allpatches$,
+the base branch starting point commit $W^{\pcn} = W$.
+
+\item
+For each $\pc$,
+the direct dependencies $\Gamma^{\pc} = \Gamma$.
+
+\item
+For each $\pc$,
+the ordered set of base branch sources $\set S^{\pcn} = \set S,
+S^{\pcn}_i = S_i$
+and corresponding merge bases $M^{\pcn}_i = M_i$.
+
+\end{itemize}
+
+\subsection{Proof of termination}
+
+$\alg{Rank-Recurse}(\pc)$ recurses but only downwards through the
+finite graph $\hasdirdep$, so it must terminate.
+
+The whole ranking algorithm iterates but each iteration involves
+adding one or more patches to $\allpatches$. Since there are
+finitely many patches and we never remove anything from $\allpatches$
+this must complete eventually.
+
+$\qed$
+
+\section{Traversal phase}
+
+(In general, unless stated otherwise below, when we generate a new
+commit $C$ using one of the commit kind algorith, we update
+$W \assign C$. In any such case where we say we're going to Merge
+with $L = W$, if $R \ge W$ we do not Merge but instead simply set
+$W \assign R$.)
+
+
+For each patch $\pc \in \allpatches$ in topological order by $\hasdep$,
+lowest first:
+
+\begin{enumerate}
+
+\item Optionally, attempt
+ $\alg{Merge-Base}(\pc)$. This may or may not succeed.
+
+\item If this didn't succeed, or was not attempted, execute
+ $\alg{Recreate-Base}(\pc)$.
+
+\item Then in any case, execute
+ $\alg{Merge-Tip}(\pc)$.
+
+\end{enumerate}
+
+After processing each $\pc$ we will have created:
+
+\begin{itemize}
+
+\item $\tipcn$ and $\tipcy$ such that $\baseof{\tipcy} = \tipcn$.
+
+\end{itemize}
+
+\subsection{$\alg{Merge-Base}(\pc)$}
+
+This algorithm attempts to construct a suitably updated version of the
+base branch $\pcn$ using some existing version of $\pcn$ as a starting
+point.
+
+It should be executed noninteractively. Specifically, if any step
+fails with a merge conflict, the whole thing should be abandoned.
+This avoids asking the user to resolve confusing conflicts. It also
+avoids asking the user to pointlessly resolve conflicts in situations
+where we will later discover that $\alg{Merge-Base}$ wasn't feasible
+after all.
+
+If $\pc$ has only one direct dependency, this algorithm should not be
+used as in that case $\alg{Recreate-Base}$ is trivial and guaranteed
+to generate a perfect answer, whereas this algorithm might involve
+merges and therefore might not produce a perfect answer if the
+situation is complicated.
+
+Initially, set $W \iassign W^{\pcn}$.
+
+\subsubsection{Bases and sources}
+
+In some order, perhaps interleaving the two kinds of merge:
+
+\begin{enumerate}
+
+\item For each $\pd \isdirdep \pc$, find a merge base
+$M \le W,\; \le \tipdy$ and merge $\tipdy$ into $W$.
+That is, use $\alg{Merge}$ with $L = W,\; R = \tipdy$.
+(Dependency Merge.)
+
+\item For each $S \in S^{\pcn}_i$, merge it into $W$.
+That is, use $\alg{Merge}$ with $L = W,\; R = S,\; M = M^{\pcn}_i$.
+(Base Sibling Merge.)
+
+\end{enumerate}
+
+\subsubsection{Fixup}
-The planning phase computes:
-\begin{itemize*}
-\item{ The relation $\hasdirdep$ and hence the ordering $\hasdep$. }
-\item{ For each commit set $\pc$, the order in which to merge
- $E_{\pc,j} \in \set E_{\pc}$. }
-\item{ For each $E_{\pc,j}$ an intended merge base $M_{\pc,j}$. }
-\end{itemize*}
+Execute $\alg{Fixup-Base}(W,\pc)$.
-We use a recursive planning algorith, recursing over Topbloke commit
-sets (ie, sets $\py$ or $\pn$). We'll call the commit set we're
-processing at each step $\pc$.
-At each recursive step
-we make a plan to merge all $\set E_{\pc} = \{ E_{\pc,j \ldots} \}$
-and all the direct contributors of $\pc$ (as determined below)
-into $\grefzc$, to make $\greffc$.
-We start with $\pc = \pl$ where $\pl = \patchof{L}$.
+\subsection{$\alg{Recreate-Base}(\pc)$}
+\begin{enumerate}
-\subsection{Direct contributors for $\pc = \pcn$}
+\item
-The direct contributors of $\pcn$ are the commit sets corresponding to
-the tip branches for the direct dependencies of the patch $\pc$. We
-need to calculate what the direct dependencies are going to be.
+Choose a $\hasdep$-maximal direct dependency $\pd$ of $\pc$.
-Choose an (arbitrary, but ideally somehow optimal in
-a way not discussed here) ordering of $\set E_{\pc}$, $E_{\pc,j}$
-($j = 1 \ldots m$).
-For brevity we will write $E_j$ for $E_{\pc,j}$.
-Remove from that set (and ordering) any $E_j$ which
-are $\le$ and $\neq$ some other $E_k$.
+\item
-Initially let $\set D_0 = \depsreqof{\grefzc}$.
-For each $E_j$ starting with $j=1$ choose a corresponding intended
-merge base $M_j$ such that $M_j \le E_j \land M_j \le T_{\pc,j-1}$.
-Calculate $\set D_j$ as the 3-way merge of the sets $\set D_{j-1}$ and
-$\depsreqof{E_j}$ using as a base $\depsreqof{M_j}$. This will
-generate $D_m$ as the putative direct contributors of $\pcn$.
+Use $\alg{Create Base}$ with $L$ = $\pdy,\; \pq = \pc$ to generate $C$
+and set $W \iassign C$. (Recreate Base Beginning.)
-However, the invocation may give instructions that certain direct
-dependencies are definitely to be included, or excluded. As a result
-the set of actual direct contributors is some arbitrary set of patches
-(strictly, some arbitrary set of Topbloke tip commit sets).
+\item
-\subsection{Direct contributors for $\pc = \pcy$}
+Execute the subalgorithm $\alg{Recreate-Recurse}(\pc)$.
-The sole direct contributor of $\pcy$ is $\pcn$.
+\item
-\subsection{Recursive step}
+Declare that we contain all of the relevant information from the
+sources. That is, use $\alg{Pseudo-merge}$ with $L = W, \;
+\set R = \{ W \} \cup \set S^{\pcn}$.
+(Recreate Base Final Declaration.)
-For each direct contributor $\p$, we add the edge $\pc \hasdirdep \p$
-and augment the ordering $\hasdep$ accordingly.
+\end{enumerate}
-If this would make a cycle in $\hasdep$, we abort . The operation must
-then be retried by the user, if desired, but with different or
-additional instructions for modifying the direct contributors of some
-$\pqn$ involved in the cycle.
+\subsubsection{$\alg{Recreate-Recurse}(\pd)$}
-For each such $\p$, after updating $\hasdep$, we recursively make a plan
-for $\pc' = \p$.
+\begin{enumerate}
-\section{Execution phase}
+\item Is $W \haspatch \pd$ ? If so, there is nothing to do: return.
+\item TODO what about non-Topbloke base branches
+\item Use $\alg{Pseudo-Merge}$ with $L = W,\; \set R = \{ \tipdn \}$.
+(Recreate Base Dependency Base Declaration.)
+\item For all $\hasdep$-maximal $\pd' \isdirdep \pd$,
+execute $\alg{Recreate-Recurse}(\pd')$.
-with $M=M_j, L=T_{\pc,j-1}, R=E_j$,
-and calculate what the resulting desired direct dependencies file
-(ie, the set of patches $\set D_j$)
-would be. Eventually we
+\item Use $\alg{Merge}$ to apply $\pd$ to $W$. That is,
+$L = W, \; R = \tipdy, \; M = \baseof{R} = \tipdn$.
+(Recreate Reapply.)
-So, formally, we select somehow an order of sources $S_i$. For each
+\end{enumerate}
-Make use of the following recursive algorithm, Plan
+\subsection{$\alg{Merge-Tip}(\pc)$}
+\begin{enumerate}
+\item TODO CHOOSE/REFINE W AND S as was done during Ranking for bases
+\item $\alg{Merge}$ from $\tipcn$. That is, $L = W, \;
+R = \tipcn$ and choose any suitable $M$. (Tip Base Merge.)
- recursively make a plan to merge all $E = \pends$
+\item For each source $S \in \set S^{\pcy}$,
+$\alg{Merge}$ with $L = W, \; R = S$ and any suitable $M$.
+(Tip Source Merge.)
-Specifically, in
+\end{enumerate}
~ian / topbloke-formulae.git / blobdiff