X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=topbloke-formulae.git;a=blobdiff_plain;f=strategy.tex;h=bfd392224d6e5c854573b4988f4314fd66d40530;hp=50efed7c8598cbf61a0e9b349b9dece2e3634267;hb=d29c556b0ebedf4081684216f426b83ee9f04573;hpb=d38e61b9455e0d0d4e9faadf5df29bb75a125331

diff --git a/strategy.tex b/strategy.tex
index 50efed7..bfd3922 100644
--- a/strategy.tex
+++ b/strategy.tex
@@ -1,11 +1,27 @@
-\section{Strategy}
-
-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 $\patchof{L}$.
-
-\subsection{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}
@@ -15,77 +31,81 @@ for $\patchof{L}$.
 The set of direct dependencies (in the form $\py$)
 requested in the commit $K$ ($K \in \pn$) for the patch $\p$.
 
-\item[ $\pc \succ_1 \{ \p, \pq \ldots \}$ ]
-The Topbloke commit set $\pc$ has as direct contributors
-(see below) exactly $\p, \pq, \ldots$.  This is an acyclic relation.
+\item[ $\pc \hasdirdep \p$ ]
+The patch $\pc$ has as a direct dependency the
+patch $\p$.  This is an acyclic relation.
 
-\item[ $\p \succ \pq$ ]
-The commit set $\p$ has as direct or indirect contributor the commit
-set $\pq$.
-This is an acyclic relation, and is the completion of $\succ_1$ into a
+\item[ $\p \hasdep \pq$ ]
+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.
-
-\end{basedescript}
-
-\subsection{Planning phase}
-
-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 $\pc$.  We start with $\pc = \pl$
-where $\pl = \patchof{L}$.
-
-At each recursive step 
-we intend to merge all $\set E_{\pc} = \{ E_{\pc,j \ldots} \}$
-and all the direct contributors of $\pc$ (as determined below)
-into the existing git ref for $\pc$, to make $T_{\pc}$.
-The direct contributors of $\pcn$ are the Topbloke commit sets
-corresponding to the tip branches for the direct dependencies of
-$\pc$.
-The sole direct contributor of $\pcy$ is $\pcn$.
-
-\subsubsection{Planning step for $\pc = \pcn$.}
-
-Choose an (arbitrary, but ideally somehow optimal in
-a way not discussed here) ordering of $\set E_{\pc}$, $E_j$ (for
-$j = 1 \ldots m$).  Remove from that set (and ordering) any $E_j$ which
-are $\le$ and $\neq$ some other $E_k$.
-
-Initially let $T_{\pc,0}$ be the git ref for $\pcn$.  And let
-$\set D_0 = \depsreqof{T_{\pc,0}}$.
-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 for $\pcn$.
-
-However, the invocation may specify 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.
-
+\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[ $\allsrcs$ ]
+$\bigcup_{\p \in \allpatches} \set H^{\pn} \cup \set H^{\py}$.
+All the input commits to the update algorithm.  (See below.)
 
+%\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.
 
-Imagine that we will merge the direct 
+\end{basedescript}
 
-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 
+\stdsection{Inputs to the update algorithm}
 
-So, formally, we select somehow an order of sources $S_i$.  For each 
+\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}
 
-Make use of the following recursive algorithm, Plan 
+\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 appropriate commits (and the appropriate other patches),
+as generated by the Traversal phase of the update algorithm.
 
- recursively make a plan to merge all $E = \pends$
+\end{basedescript}
 
-Specifically, in