X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=topbloke-formulae.git;a=blobdiff_plain;f=strategy.tex;h=d9a2545f1db52b98ed9d8330cd1dfd55e91c561f;hp=a3acc81ec7560dec9a0cd0e9e7b2311ac10a4194;hb=f0f7eceb4c3b65e4728d0b04b23e28906d5038fb;hpb=790de021ff6ec354b1bf53c7b57fef89074ba4f4

diff --git a/strategy.tex b/strategy.tex
index a3acc81..d9a2545 100644
--- a/strategy.tex
+++ b/strategy.tex
@@ -1,9 +1,27 @@
-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
+(which involves 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}
@@ -14,7 +32,7 @@ The set of direct dependencies (in the form $\py$)
 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
+The Topbloke commit set $\pc$ has as a direct contributor the
 commit set $\p$.  This is an acyclic relation.
 
 \item[ $\p \hasdep \pq$ ]
@@ -23,22 +41,150 @@ set $\pq$.
 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 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[ $ \tipzc, \tipcc, \tipuc, \tipfc $ ]
+%The git ref for the Topbloke commit set $\pc$: respectively,
+%the original, current, updated, and final values.
+
+\end{basedescript}
 
-\item[ $ \tipzc, \tipcc, \tipuc, \tipfc $ ]
-The git ref for the Topbloke commit set $\pc$: respectively,
-the original, current, updated, and final values.
+\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 $\pc^{+/-}$.
+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) relation $\hasdirdep$.
 
 \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 {\bf Rank-Recurse}($\pc_0$)
+\item Until $\allpatches$ remains unchanged.
+\end{enumerate}
+\end{enumerate}
+
+{\bf Rank-Recurse}($\pc$) is:
+\begin{enumerate}
+
+\item If we have already done {\bf Rank-Recurse}($\pc$) in this
+ranking iteration, do nothing.  Otherwise:
+
+\item Add $\pc$ to $\allpatches$ if it is not there already.
+
+\item Let
+$$
+  \set S = h(\pcn)
+     \cup 
+        \bigcup_{\p \in \allpatches}
+        \bigcup_{H \in h(\pn) \lor H \in h(\py)}
+         \{ \baseof{E} \; | \; E \in \pendsof{H}{\pcy} \}
+$$
+
+and $W = w(h(\pcn))$
+
+\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 order of $\set S$, $S_i$ for $i=1 \ldots n$.
+
+\item For each $S_i$ in turn, choose a corresponding $M_i$
+such that $$
+   M_i \le S_i \land \left[
+   M_i \le W \lor \bigexists_{S_i, j<i} M_i \le s_i
+   \right]
+$$
+
+\item Set $\Gamma = \depsreqof{W}$.
+
+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:
+$$
+\Gamma \assign \text{\bf set-merge}\left(\Gamma, 
+ \left[ \begin{cases} 
+  M_i \in \pcn :     & \depsreqof{M_i} \\
+  M_i \not\in \pcn : & \{ \}
+ \end{cases} \right],
+ \depsreqof{S_i}
+ \right)
+$$
+
+\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.)
+\end{enumerate}
+\item Run ${\text{\bf Rank-Recurse}}(\pd)$.
+
+\end{enumerate}
+
+The results of the ranking phase are:
+
+$ \allpatches, \hasdirdep $ and hence the completion of $\hasdirdep$
+into the partial order $\hasdep$.
+
+For each $\pc$, the base branch starting point commit $W_{\pcn} = W$,
+the direct dependencies $\Gamma_{\pc}$,
+the ordered set of base branch sources $\set S_{\pcn} = \set S,
+S_{\pcn,i} = S_i$
+and corresponding merge bases $M_{\pcn,i} = M_i$.
+
+
+
 \section{Planning phase}
 
-The planning phase computes: 
+The results of the planning phase consist of: 
 \begin{itemize*}
-\item{ The relation $\hasdirdep$ and hence the ordering $\hasdep$. }
-\item{ For each commit set $\pc$, the order in which to merge
+\item{ The relation $\hasdirdep$ and hence the partial order $\hasdep$. }
+\item{ For each commit set $\pc$, a confirmed set of sources $\set S_{\pc}$. }
+\item{ For each commit set $\pc$, the order in which to merge the sources
         $E_{\pc,j} \in \set E_{\pc}$. }
 \item{ For each $E_{\pc,j}$ an intended merge base $M_{\pc,j}$. }
 \end{itemize*}
@@ -130,16 +276,16 @@ it is, are we fast forward to $E_i$
 and drop $E_i$ from the planned ordering.
 
 Then we will merge the direct contributors and the sources' ends.
-
 This generates more commits $\tipuc \in \pc$, but none in any other
-commit set.  We maintain XXX FIXME IS THIS THE BEST THING?
+commit set.  We maintain
 $$
  \bigforall_{\p \isdep \pc}
- \pancsof{\tipcc}{\p} \subset \left[
-   \tipfa \p \cup
-   \bigcup_{E \in \set E_{\pc}} \pancsof{E}{\p}
-  \right]
+ \pancsof{\tipcc}{\p} \subset
+   \pancsof{\tipfa \p}{\p}
 $$
+\proof{
+ For $\tipcc = \tipzc$, $T$ ...WRONG WE NEED $\tipfa \p$ TO BE IN $\set E$ SOMEHOW
+}
 
 \subsection{Merge Contributors for $\pcy$}
 
@@ -147,16 +293,18 @@ Merge $\pcn$ into $\tipc$.  That is, merge with
 $L = \tipc, R = \tipfa{\pcn}, M = \baseof{\tipc}$.
 to construct $\tipu$.
 
-Merge conditions: Ingredients satisfied by construction.
+Merge conditions:
+
+Ingredients satisfied by construction.
 Tip Merge satisfied by construction.  Merge Acyclic follows
 from Perfect Contents and $\hasdep$ being acyclic.
 
-Removal Merge Ends: For $\p = \pc$, $M \nothaspatch \p$.
-For $p \neq \pc$, by Tip Contents,
+Removal Merge Ends: For $\p = \pc$, $M \nothaspatch \p$; OK.
+For $\p \neq \pc$, by Tip Contents,
 $M \haspatch \p \equiv L \haspatch \p$, so we need only
 worry about $X = R, Y = L$; ie $L \haspatch \p$,
 $M = \baseof{L} \haspatch \p$.
-By Tip Contents for $L$, $D \le L \equiv D \le M$.  $\qed$
+By Tip Contents for $L$, $D \le L \equiv D \le M$.  OK.~~$\qed$
 
 WIP UP TO HERE
 
@@ -167,6 +315,10 @@ $R \haspatch \p$.  So we only need to worry about $Y = R = \tipfa \pcn$.
 By Tip Dependencies $\tipfa \pcn \ge \tipfa \py$.
 And by Tip Sources $\tipfa \py \ge $
 
+want to prove $E \le \tipfc$ where $E \in \pendsof{\tipcc}{\py}$
+
+$\pancsof{\tipcc}{\py} = $
+
 
 computed $\tipfa \py$, and by Perfect Contents for $\py$