* update ghc-lib patch
* update stack-snapshot.yaml
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* bazel run @stackage-unpinned//:pin (on linux) and update stackage_snapshot.json
* testcase to check type signatures in template-lets are not ignored
* update to ghc-lib commit hash following merge
* update snapshot
* update snapshot after pin on windows
* update stack pin on linux
Co-authored-by: Nick Chapman <nchapman@digitalasset.com>
* Adapt to new desugaring for choice observers.
update hash of ghc patch.
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update ghc patch to final version
update stack-snapshot hashes for ghc-lib(-parser)
update stackage_snapshot.json, following `bazel run @stackage-unpinned//:pin`
expose Optional constructors for desugared code to use
adapt LFConversion to expect a 4-tuple for a desugared choice def/sig
update LFConversion for choice-observers
first example using new choice observer syntax.
fix scala type checker to have correct scoping rules for choice-observers
remove comment from example which says it is broken
improve variable names
improve tests for choice-observer clause
only test choice-observers SINCE 1.dev
add jq queries for choice observeres
make positive statement in jq test which checks choice obserers are present
test behaviour of choice observers
squash me
typo
* test more choice-observer divulgence
* Update documention for choice observers.
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Support choice observers in 1.dev
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* fix docs build
* fix daml docs choice-observers example
* address comments: rewording text
* annotate choices observers as early-access in documention
* split out documentation code-snippets which require --target=1.dev
* final tweaks to documentation text
* Fix reference to return produced by ApplicativeDo
see https://github.com/digital-asset/ghc/pull/53 for details.
fixes#6820
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* bump to merged commit
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* switch to new ghc-lib
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fixes#3150
This PR introduces a patch to GHC to fix the performance of the
pattern match checker in the presence of multiple packages which
is currently significantly (orders of magnitude) slower than having
everything in a single package. I also added a test case that hits
this. Here’s what you need to hit this issue:
1. A typeclass with a functional dependency. `HasField` is the obvious
candidate for this.
2. A lot of instances of this typeclass in a separate package (this is
the only part where the separate package matters).
3. A reasonably large ADT with a bunch of strict fields.
4. A pattern match in the context of some constraints of the
typeclass. The constraints can be completely unused.
In that case, you will get a significant slowdown in the number of
instances, number of constructors and number of constraints (didn’t
verify if it’s linear but it is significant which is all that
matters).
Here’s why this happens:
1. The pattern match checker checks for strict fields if the type is
inhabited.
2. This calls `pmTopNormaliseType_maybe` to normalize a type (the details don’t
matter) which in turn calls into the typechecker. This function is
called very often (presumably linear in the number of constructors
but didn’t verify.)
3. The typechecker has some logic in `improveFromInstEnv` for
generating additional equations by unifying functional
dependencies `a -> b` with constraints in scope
and thereby deducing information about `b`.
4. In the pattern match checker the list of instances of the home
package is empty since the pattern match checker (apparently)
doesn’t actually care about those extra equations. However, the
list of instances in the EPS is not empty. This is the issue here:
By moving it to an external package we suddenly end up with
thousands of instances that we try to unify with the functional
dependencies every time we normalize which happens very often.
Proposed fix:
The solution is rather simple: Since the pattern match checker
apparently does not care about the instances of the home package, it
almost certainly doesn’t care about instances in general so we just
empty the instances of external packages explicitly.
Is the fix correct?
1. I verified that the GHC test suite passes with this patch which
gives me a reasonable level of confidence.
2. I verified that our own test suite passes.
3. The most dodgy part is actually emptying the instance since the
whole EPS stuff is a mutable mess. What could in theory happen is that
the PM ends up loading an interface file that mutates this
again. However, afaiu it is impossible for the PM to need an
interface that the typechecker didnt already need. I did do a bunch
of debugging and this is exactly what I observed in my experiments.
Alternative ideas and upstreaming:
The other option would be to not try and mess with the EPS but somehow
have a conditional flag somewhere in the typechecker env to disable
this logic in the pattern match checker. However, that sounds
significantly more complex so I don’t think it’s worth the effort.
GHC 8.10 has a new pattern match checker that has different
performance characteristics and seems to do much better here so there
is little reason to try and upstream this. I strongly want to avoid
upgrading DAML to 8.10 at this point (too much risk, let’s wait until
things calm down)
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- [DAML Compiler] Fix an issue where compilation slowed down
significantly when code was split up into several packages. See
https://github.com/digital-asset/daml/issues/3150
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automated ghc-lib build
This PR aims at automating the build of ghc-lib. The current process
still has a few manual steps; it needs to be updated because Bintray is
going away, so this seemed like a good opportunity to fully automate it.
This works like the "patch bazel on Windows" jobs: the filename will
contain a hash of the `ci/da-ghc-lib` folder, and the job will run only
if the corresponding filename does not yet exist on the GCS bucket. PRs
aiming at changing the ghc-lib version will need to run twice: once to
create the artifacts, and once to change the `stack-snapshot.yaml` file
to match.
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