`copilot-language`: test compile error about copilot

[swt2c]

Thanks @ivanperez-keera I'll try putting that patch in tonight.

[swt2c]

Thanks @ivanperez-keera, I can confirm this patch gets copilot back to a green board in Debian (ignore mips64el). :-)

[ivanperez-keera]

Thanks a lot! Will review it and get back to you.

[swt2c]

Are you able to reproduce this one locally, or do you need any more info from me on it?

[ivanperez-keera]

I'm trying to reproduce it in a docker container with GHC 9.4.7 and Cabal 3.8. Cabal is giving me headaches: haskell/cabal#9444.

[ivanperez-keera]

I managed to reproduce the problem.

[swt2c]

Hey Ivan, just checking in to see if this was looking relatively easy to fix, or whether it might take a bit to sort out. I think this is the last (known) blocker in getting copilot updated in Debian. Obviously not the most urgent issue in the world, though. :-)

[ivanperez-keera]

Hi. I'm hoping we'll be able to fix this soon. I don't know if I'll be able to find time this week but I'll do everything I can. If not, I'll prioritize fixing this by next week.

And thanks for following up on this! Having Copilot in Debian is a big deal for us and your support to make that happen is invaluable :)

[ivanperez-keera]

@swt2c I was able to find the solution. I'll try to push this soon.

If you want to backport this change to Copilot 3.17 on Debian, here's the diff:

diff --git a/copilot-language/tests/Test/Copilot/Language/Reify.hs b/copilot-language/tests/Test/Copilot/Language/Reify.hs
index e056d946..d724df73 100644
--- a/copilot-language/tests/Test/Copilot/Language/Reify.hs
+++ b/copilot-language/tests/Test/Copilot/Language/Reify.hs
@@ -31,7 +31,7 @@ import qualified Copilot.Language.Operators.Integral as Copilot
 import qualified Copilot.Language.Operators.Mux      as Copilot
 import qualified Copilot.Language.Operators.Ord      as Copilot
 import           Copilot.Language.Reify              (reify)
-import           Copilot.Language.Spec               (observer)
+import           Copilot.Language.Spec               (Spec, observer)
 import           Copilot.Language.Stream             (Stream)
 import qualified Copilot.Language.Stream             as Copilot
 
@@ -732,7 +732,8 @@ semanticsShowK steps (SemanticsP (expr, exprList)) =
 checkSemanticsP :: Int -> [a] -> SemanticsP -> IO Bool
 checkSemanticsP steps _streams (SemanticsP (expr, exprList)) = do
     -- Spec with just one observer of one expression.
-    let spec = observer testObserverName expr
+    let spec :: Spec
+        spec = observer testObserverName expr
 
     -- Reified stream (low-level)
     llSpec <- reify spec

[ivanperez-keera]

Description

copilot-language's tests fail to compile with GHC 9.4. Prior versions made arbitrary decisions during type interfence, and the new type checker will simply reject such programs.

Type

• Bug: test fails to compile.

Additional context

None.

Requester

• Scott Talbert (Debian Developer & Debian Haskell Group)

Method to check presence of bug

Compiling copilot-language's tests with GHC 9.4.7 results in an error message:

# cabal test .
Build profile: -w ghc-9.4.7 -O1
In order, the following will be built (use -v for more details):
 - copilot-language-3.17 (test:unit-tests) (first run)
Preprocessing test suite 'unit-tests' for copilot-language-3.17..
Building test suite 'unit-tests' for copilot-language-3.17..
[2 of 3] Compiling Test.Copilot.Language.Reify ( tests/Test/Copilot/Language/Reify.hs, /root/copilot/dist-newstyle/build/x86_64-linux/ghc-9.4.7/copilot-language-3.17/t/unit-tests/build/unit-tests/unit-tests-tmp/Test/Copilot/Language/Reify.o )

tests/Test/Copilot/Language/Reify.hs:737:16: error:
    * Could not deduce (Copilot.Core.Type.Struct t)
        arising from a superclass required to satisfy `Typed t',
        arising from a use of `observer'
      from the context: (Read t, Eq t, Typed t, Arbitrary t)
        bound by a pattern with constructor:
                   SemanticsP :: forall t.
                                 (Typeable t, Read t, Eq t, Show t, Typed t, Arbitrary t) =>
                                 ((Typeable t, Read t, Eq t, Show t, Typed t, Arbitrary t) =>
                                  (Stream t, [t]))
                                 -> SemanticsP,
                 in an equation for `checkSemanticsP'
        at tests/Test/Copilot/Language/Reify.hs:734:33-59
      Possible fix:
        add (Copilot.Core.Type.Struct t) to the context of
          the data constructor `SemanticsP'
    * In the expression: observer testObserverName expr
      In an equation for `spec': spec = observer testObserverName expr
      In the expression:
        do let spec = observer testObserverName expr
           llSpec <- reify spec
           let trace = eval Haskell steps llSpec
           let expectation = take steps exprList
           ....
    |
737 |         spec = observer testObserverName expr

Expected result

The above tests should compile without errors.

Desired result

The above tests should compile without errors.

Proposed solution

Add type annotations in checkSemanticsP.

Further notes

None.

[ivanperez-keera]

Change Manager: Confirmed that the issue manifests with GHC 9.4.

[ivanperez-keera]

Technical Lead: Confirmed that the issue should be addressed.

[ivanperez-keera]

Technical Lead: Bug scheduled for fixing in Copilot 3.18.

Fix assigned to: @ivanperez-keera.

[ivanperez-keera]

Implementor: Solution implemented, review requested.

[ivanperez-keera]

Change Manager: Verified that:

• Solution is implemented:
  • The code proposed compiles and passes all tests. Details:
    Build log: https://app.travis-ci.com/github/Copilot-Language/copilot/builds/267903584
  • The solution proposed produces the expected result. Details:
    The following Dockerfile checks that copilot-language compiles with GHC 9.4, in which case it prints the message Success:

    FROM ubuntu:focal
    
    RUN apt-get update
    
    RUN apt-get install --yes libz-dev
    RUN apt-get install --yes git
    
    RUN apt-get install --yes wget
    RUN mkdir -p $HOME/.ghcup/bin
    RUN wget https://downloads.haskell.org/~ghcup/0.1.19.2/x86_64-linux-ghcup-0.1.19.2 -O $HOME/.ghcup/bin/ghcup
    
    RUN chmod a+x $HOME/.ghcup/bin/ghcup
    ENV PATH=$PATH:/root/.ghcup/bin/
    ENV PATH=$PATH:/root/.cabal/bin/
    RUN apt-get install --yes curl
    RUN apt-get install --yes gcc make libgmp3-dev g++
    
    SHELL ["/bin/bash", "-c"]
    
    RUN ghcup install ghc 9.4.7
    RUN ghcup install cabal 3.8
    RUN ghcup set ghc 9.4.7
    RUN cabal update
    
    CMD git clone $REPO && \
        cd $NAME && \
        git checkout $COMMIT && \
        cd copilot-language && \
        cabal test . && \
        echo Success

    Command (substitute variables based on new path after merge):

    docker run -e "REPO=https://github.com/ivanperez-keera/copilot" -e "NAME=copilot" -e "COMMIT=e25c7afaf743a5fdc7a9638516f59b006383bef0" -it copilot-verify-469
    

• Implementation is documented. Details:
  Internal change; no changes to the documentation are needed, and a comment is added to ensure that future revisions do not remove the change accidentally.
• Change history is clear.
• Commit messages are clear.
• Changelogs are updated.
• Examples are updated. Details:
  No updates needed.
• Required version bumps are evaluated. Details:
  Bump not needed (internal change to tests; does not affect API).

[ivanperez-keera]

Change Manager: Implementation ready to be merged.