Introduce "setup dependencies" #2515
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It turns out not to be the right solution for general private dependencies and is just complicated. However we keep qualified goals, just much simpler. Now dependencies simply inherit the qualification of their parent goal. This gets us closer to the intended behaviour for the --independent-goals feature, and for the simpler case of private dependencies for setup scripts. When not using --independent-goals, the solver behaves exactly as before (tested by comparing solver logs for a hard hackage goal). When using --independent-goals, now every dep of each independent goal is qualified, so the dependencies are solved completely independently (which is actually too much still).
POption annotates a package choice with a "linked to" field. This commit just introduces the datatype and deals with the immediate fallout, it doesn't actually use the field for anything.
This is implemented as a separate pass so that it can be understood independently of the rest of the solver.
In particular, in the definition of dependencyInconsistencies. One slightly annoying thing is that in order to validate an install plan, we need to know if the goals are to be considered independent. This means we need to pass an additional Bool to a few functions; to limit the number of functions where this is necessary, also recorded whether or not goals are independent as part of the InstallPlan itself.
Since we didn't really have a unit test setup for the solver yet, this introduces some basic tests for solver, as well as tests for independent goals specifically.
This address @23Skidoo's comment #2500 (comment)
I don't know why we we constructed this graph manually here rather than calling `graphFromEdges`; it doesn't really matter except that we will want to change the structure of this graph somewhat once we have more fine-grained dependencies, and then the manual construction becomes a bit more painful; easier to use the standard construction.
This commit does nothing but rearrange the Modular.Dependency module into a number of separate sections, so that's a bit clearer to see what's what. No actual code changes here whatsoever.
The ComponentDeps datatype will give us fine-grained information about the dependencies of a package's components. This commit just introduces the datatype, we don't use it anywhere yet.
The modular solver has its own representation for a package (PInfo). In this commit we modify PInfo to keep track of the different kinds of dependencies. This is a bit intricate because the solver also regards top-level goals as dependencies, but of course those dependencies are not part of any 'component' as such, unlike "real" dependencies. We model this by adding a type parameter to FlaggedDeps and go which indicates whether or not we have component information; crucially, underneath flag choices we _always_ have component information available. Consequently, the modular solver itself will not make use of the ComponentDeps datatype (but only using the Component type, classifying components); we will use ComponentDeps when we translate out of the results from the modular solver into cabal-install's main datatypes. We don't yet _return_ fine-grained dependencies from the solver; this will be the subject of the next commit.
In this commit we modify the _output_ of the modular solver (CP, the modular's solver internal version of ConfiguredPackage) to have fine-grained dependency. This doesn't yet modify the rest of cabal-install, so once we translate from CP to ConfiguredPackage we still lose the distinctions between different kinds of dependencies; this will be the topic of the next commit. In the modular solver (and elsewhere) we use Data.Graph to represent the dependency graph (and the reverse dependency graph). However, now that we have more fine-grained dependencies, we really want an _edge-labeled_ graph, which unfortunately it not available in the `containers` package. Therefore I've written a very simple wrapper around Data.Graph that supports edge labels; we don't need many fancy graph algorithms, and can still use Data.Graph on these edged graphs when we want (by calling them on the underlying unlabeled graph), so adding a dependency on `fgl` does not seem worth it.
The crucial change in this commit is the change to PackageFixedDeps to return a
ComponentDeps structure, rather than a flat list of dependencies, as long with
corresponding changes in ConfiguredPackage and ReadyPackage to accomodate this.
We don't actually take _advantage_ of these more fine-grained dependencies yet;
any use of
depends
is now a use of
CD.flatDeps . depends
but we will :)
Note that I have not updated the top-down solver, so in the output of the
top-down solver we cheat and pretend that all dependencies are library
dependencies.
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/cc @kosmikus . |
Although we don't use the new setup dependency component anywhere yet, I've replaced all uses of CD.flatDeps with CD.nonSetupDeps. This means that when we do introduce the setup dependencies, all code in Cabal will still use all dependencies except the setup dependencies, just like now. In other words, using the setup dependencies in some places would be a conscious decision; the default is that we leave the behaviour unchanged.
This patch adds it to the package description types and to the parser. There is a new custom setup section which contains the setup script's dependencies. Also add some sanity checks.
(and, therefore, also to the modular solver's output)
By chosing setup dependencies after regular dependencies we get more opportunities for linking setup dependencies against regular dependencies.
The only problematic thing is that when we call `cabal clean` or `cabal
haddock` (and possibly others), _without_ first having called `configure`, we
attempt to build the setup script without calling the solver at all. This means
that if you do, say,
cabal configure
cabal clean
cabal clean
for a package with a custom setup script that really needs setup dependencies
(for instance, because there are two versions of Cabal in the global package DB
and the setup script needs the _older_ one), then first call to `clean` will
succeed, but the second call will fail because we will try to build the setup
script without the solver and that will fail.
This was referenced Apr 9, 2015
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I think the status here is that @kosmikus is happy for this to be committed, and for his comments to be addressed after merging. Right @kosmikus? The only other thing is a follow-up patch to address @23Skidoo's comment about cabal version checks. Anything else? From my point of view this is ready to go in (and we'll follow up on the comments). |
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@dcoutts |
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@23Skidoo promise :-) Thanks. (We want it to work well and be maintainable obviously) |
dcoutts
added a commit
that referenced
this pull request
May 21, 2015
Introduce "setup dependencies"
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Yay! |
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One thing that hasn't been discussed here, is what recommended backwards-compatible usage for people who don't have the newest version of Cabal? Example: ekmett/lens#496 (comment) where people want to support older versions of GHC with the stock Cabal. |
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.. And finally, the pièce de résistance, introducing suppport for setup dependencies! This PR relies on #2500, #2504 and #2514.
In this PR we add a new section to the
.cabalfile in which packages can specify explicit setup dependencies. When this section is absent (i.e., currently for all packages) we don't do anything different to what we do now, but when the section is present then that section is used to the dependencies of a setup script.For example, suppose we have two versions of package A available in our global (or user local, if not using sandboxes) DB. If we have a package whose setup script relies on version 0.1 of A, rather than version 0.2, it will fail to build because by default
cabal-installjust makes all packages visible when compiling a setup script, which means that it will be linked against the newer version.However, we can now use an explicit setup dependencies stanza to address this:
Setup dependencies are treated as independent in the solver: we can pick different versions of packages for the setup script that we pick for the package proper, although we make an attempt not to do so (as explained in the blog post about independent goals).
As a sanity check, I ran the solver after all these PRs against all (the latest versions of) all packages on Hackage (all 7889), and wherever we produce an install plan we produce the same install plan, so that's reassuring.
In addition, I also did some performance measurements, but there's hardly any difference in performance. The modified solver is slightly slower, but barely so: here's a density plot of execution time in seconds; red is stock cabal-install 1.22, blue is the solver with all my PRs:
And here's a density plot of the relative performance of the two solvers; 1.0 meaning exactly equal, below 1.0 meaning the modified solver is faster, above 1.0 meaning the modified solver is slower:
Basically, the conclusion -- performance-wise anyway -- is: no significant difference.