Support GHC 8.10

[blackgnezdo]

I'd like to get some help with supporting this new release. Some items that likely require attention:

• Getting a working build plan
• Adapting to GHC internal API changes (if any)

[jinwoo]

This at least requires ghc-source-gen also support 8.10.

[yaitskov]

github CI

Warning: Unknown/unsupported 'ghc' version detected (Cabal 3.0.2.0 supports
'ghc' version < 8.10): /opt/ghc/8.10.1/bin/ghc is version 8.10.1
Resolving dependencies...
cabal: Could not resolve dependencies:
[__0] trying: megaexample-0.4.2 (user goal)
[__1] trying: base-4.14.0.0/installed-4.1... (dependency of megaexample)
[__2] trying: opentelemetry-extra-0.4.2 (user goal)
[__3] next goal: proto-lens (dependency of opentelemetry-extra)
[__3] rejecting: proto-lens-0.6.0.0 (conflict:
base==4.14.0.0/installed-4.1..., proto-lens => base>=4.10 && <4.14)

[yaitskov]

@jinwoo , ghc-source-gen has been fixed.

[jinwoo]

@yaitskov Yeah I know (I'm the one who reviewed that change 😄 ). I just didn't have a chance to work on this. Let me do this soon unless someone else is already working.

[jinwoo]

I'm struggling with the cassava package. It fails to build with errors like below. I tried adding text-short-0.1.3 to the new stack-8.10.yaml file but it didn't work.

@judah Any magic you know of?

cassava                  > /tmp/stack-031cc73279663f7f/cassava-0.5.2.0/src/Data/Csv/Conversion.hs:26:3: error:
cassava                  >      error: #error **INVARIANT BROKEN** Detected invalid combination of `text-short` and `bytestring` versions. Please verify the `pre-bytestring-0.10-4` flag-logic in the .cabal file wasn't elided.                                      
cassava                  >        26 | # error **INVARIANT BROKEN** Detected invalid combination of `text-short` and `bytestring` versions. Please verify the `pre-bytestring-0.10-4` flag-logic in the .cabal file wasn't elided.                                       
cassava                  >           |   ^~~~~                                
cassava                  >    |                                                      
cassava                  > 26 | # error **INVARIANT BROKEN** Detected invalid combination of `text-short` and `bytestring` versions. Please verify the `pre-bytestring-0.10-4` fla
g-logic in the .cabal file wasn't elided.                                                
cassava                  >    |   ^                                            
cassava                  >                                                            
cassava                  > /tmp/stack-031cc73279663f7f/cassava-0.5.2.0/src/Data/Csv/Conversion.hs:100:0: error:
cassava                  >      warning: "MIN_VERSION_text_short" is not defined, evaluates to 0 [-Wundef]
cassava                  >       100 | #if MIN_VERSION_text_short(0,1,0)
cassava                  >           |                                 
...

[jinwoo]

haskell-hvr/cassava#177 seems to suggest that the problem is allow-newer. But we need allow-newer for GHC 8.10 until Stackage properly supports GHC 8.10. I'm not sure how to work around this.

[judah]

For ghc-source-gen, I avoided allow-newer by creating a new YAML file for 8.10 with explicit versions for all the dependencies. Stack actually helped recommend some extra-deps automatically. (I think that's because I used a custom resolver.)
https://github.com/google/ghc-source-gen/blob/83c3ccf080985670bb7859325e1f5da45b2b5d72/stack-8.10.yaml#L24

[judah]

Alternately you might be able to fix it by specifying a small number of other packages explicitly in addition to text-short: namely, those deps of cassava that are causing problems, for example, bytestring.

[jinwoo]

Well ghc-source-gen still has allow-newer: https://github.com/google/ghc-source-gen/blob/83c3ccf080985670bb7859325e1f5da45b2b5d72/stack-8.10.yaml#L45

I tried adding various packages as suggested by stack but cassava didn't work even when I specified the matching text-short and bytestring versions. I'll try again tomorrow.

[judah]

Oh, oops, I didn't realize I left it in. It turns out it's not needed, so I sent a PR to remove it: google/ghc-source-gen#72

One other thing you could try is to set Cassava's flags explicitly in the stack.yaml:
https://docs.haskellstack.org/en/stable/yaml_configuration/#flags

It looks like they set it explicitly in the LTS configuration:
https://github.com/commercialhaskell/lts-haskell/blob/8b942a5a7e93708e75ddf955184913a1ee6a68ab/lts-14.9.yaml#L12553

[jinwoo]

Oh, I saw that flag (bytestring--lt-0_10_4) yesterday but didn't think of using that. I didn't know Stackage was using it. I'll try that.

[jinwoo]

That flag was the trick!

[jinwoo]

@judah I'm seeing a test error only with GHC 8.10 like below. Any idea?

proto-lens-tests         > src/proto-lens/proto-lens-tests/tests/enum_test.hs:161:9: error: [-Woverlapping-patterns, -Werror=overlapping-patterns]
proto-lens-tests         >     Pattern match is redundant
proto-lens-tests         >     In a case alternative: Alias1 -> ...
proto-lens-tests         >     |
proto-lens-tests         > 161 |         Alias1 -> Alias1
proto-lens-tests         >     |         ^^^^^^^^^^^^^^^^
proto-lens-tests         >    
proto-lens-tests         > src/proto-lens/proto-lens-tests/tests/enum_test.hs:163:9: error: [-Woverlapping-patterns, -Werror=overlapping-patterns]
proto-lens-tests         >     Pattern match is redundant
proto-lens-tests         >     In a case alternative: Alias3 -> ...
proto-lens-tests         >     |
proto-lens-tests         > 163 |         Alias3 -> Alias3
proto-lens-tests         >     |         ^^^^^^^^^^^^^^^^
proto-lens-tests         >    

[jinwoo]

Probably something changed between 8.6 and 8.10 regarding pattern matching or pattern synonym. I'll remove those cases with GHC 8.10.