breakage with template-haskell-2.11 (in ghc-8) about derive

[ndmitchell]

I confess I'm not even certain if the Ppr Info instance is actually even needed at all. The Ppr stuff is to do fixed up pretty printing in GHC, and that might have been fixed at source long ago. I'll take a quick look, but I don't think anything in that migration guide is cause for concern.

[jwaldmann]

That sounds promising.

[ndmitchell]

I've deleted the Ppr module entirely, and everything still works fine. Could you share whatever other modifications you made? I don't have time at the moment to fix up the pieces, but I suspect a lot of CPP and a bit of time will be all that is required. If you are unable to, I'll take a look, probably next week sometime.

[jwaldmann]

OK, I'll look at it.

[jwaldmann]

I was busy with other things. I will try something in the next days.

[deepfire]

Is there any progress on this issue?

[deepfire]

One fairly important package held up by this issue is compdata, a Data Types a la Carte implementation by Bahr and Hvitved.

An example of how they employ derive:

• internally: https://github.com/pa-ba/compdata/blob/a74bfa930b646c7bcc603c74d9ba496c2022935b/src/Data/Comp/DeepSeq.hs
• as user-facing API: https://github.com/pa-ba/compdata/blob/master/examples/Examples/Thunk.hs

@ndmitchell, what do you think would be the easiest way for compdata to move ahead?

[ndmitchell]

@jwaldmann - are you still likely to be able to make the necessary changes?

@deepfire - if not, I'll update it, probably towards the end of the week (paper deadline on Wednesday).

[jwaldmann]

(sorry for the delay) I have a set of commits here ( jwaldmann@26572d0 and previous ) but it's not finished. It compiles but I doubt it works. See https://github.com/jwaldmann/derive/blob/master/Language/Haskell/Convert.hs#L116

[ndmitchell]

@jwaldmann - I've merged all your changes. One minor tweak, I prefer to use __GLASGOW_HASKELL__ as the CPP rather than template_haskell. I appreciate that in theory the second form is cleaner, but in practice only one compiler has Template Haskell, and it's always been very specifically tied to the internals of GHC at a particular version. By using the GHC macro it works more easily in GHCi.

[ndmitchell]

OK, with all those patches the test suite now works on GHC 8.0. I intend to release with that unless @jwaldmann advises against it. Ignoring a data type context is not the end of the world - in general it's a complete misfeature and rarely used.

[ndmitchell]

I've released 2.5.24 which works on GHC 8.0 and passes all the tests. Thanks a lot @jwaldmann! @deepfire, please report if there are still problems.

[deepfire]

@ndmitchell, this is what I get with GHC 8.0.1-rc4 (which saw another TH change, AIUI):

these derivations will be built:
  /nix/store/ripjal00hdc9xf9dzanhrcry9g0rj94s-derive-2.5.24.drv
building path(s) ‘/nix/store/izvyps3gi703y6ns4fz4m42hh1l7q9zw-derive-2.5.24’
setupCompilerEnvironmentPhase
Build with /nix/store/57zrq025ih51wf09zi7i03jnkr16957h-ghc-8.0.0.20160421.
unpacking sources
unpacking source archive /nix/store/rz3fcjrgqd5ymwzcy0k8vjh8jxb6a4pk-derive-2.5.24.tar.gz
source root is derive-2.5.24
setting SOURCE_DATE_EPOCH to timestamp 1458759573 of file derive-2.5.24/src/Language/Haskell/TH
/Peephole.hs
patching sources
compileBuildDriverPhase
setupCompileFlags: -package-db=/tmp/nix-build-derive-2.5.24.drv-0/package.conf.d -j8 -threaded
[1 of 1] Compiling Main             ( Setup.hs, /tmp/nix-build-derive-2.5.24.drv-0/Main.o )
Linking Setup ...
configuring
configureFlags: --verbose --prefix=/nix/store/izvyps3gi703y6ns4fz4m42hh1l7q9zw-derive-2.5.24 --
libdir=$prefix/lib/$compiler --libsubdir=$pkgid --with-gcc=gcc --package-db=/tmp/nix-build-deri
ve-2.5.24.drv-0/package.conf.d --ghc-option=-optl=-Wl,-rpath=/nix/store/izvyps3gi703y6ns4fz4m42
hh1l7q9zw-derive-2.5.24/lib/ghc-8.0.0.20160421/derive-2.5.24 --enable-split-objs --disable-libr
ary-profiling --disable-profiling --enable-shared --enable-library-vanilla --enable-executable-
dynamic --enable-tests
Configuring derive-2.5.24...
Dependency base ==4.*: using base-4.9.0.0
Dependency bytestring -any: using bytestring-0.10.8.0
Dependency containers -any: using containers-0.5.7.1
Dependency derive -any: using derive-2.5.24
Dependency directory -any: using directory-1.2.6.2
Dependency filepath -any: using filepath-1.4.1.0
Dependency haskell-src-exts ==1.17.*: using haskell-src-exts-1.17.1
Dependency pretty -any: using pretty-1.1.3.3
Dependency process -any: using process-1.4.2.0
Dependency syb -any: using syb-0.6
Dependency template-haskell -any: using template-haskell-2.11.0.0
Dependency transformers >=0.2: using transformers-0.5.2.0
Dependency uniplate >=1.5 && <1.7: using uniplate-1.6.12
Using Cabal-1.24.1.0 compiled by ghc-8.0
Using compiler: ghc-8.0.0.20160421
Using install prefix:
/nix/store/izvyps3gi703y6ns4fz4m42hh1l7q9zw-derive-2.5.24
Binaries installed in:
/nix/store/izvyps3gi703y6ns4fz4m42hh1l7q9zw-derive-2.5.24/bin
Libraries installed in:
/nix/store/izvyps3gi703y6ns4fz4m42hh1l7q9zw-derive-2.5.24/lib/ghc-8.0.0.20160421/derive-2.5.24
Private binaries installed in:
/nix/store/izvyps3gi703y6ns4fz4m42hh1l7q9zw-derive-2.5.24/libexec
Data files installed in:
/nix/store/izvyps3gi703y6ns4fz4m42hh1l7q9zw-derive-2.5.24/share/x86_64-linux-ghc-8.0.0.20160421
/derive-2.5.24
Documentation installed in:
/nix/store/izvyps3gi703y6ns4fz4m42hh1l7q9zw-derive-2.5.24/share/doc/x86_64-linux-ghc-8.0.0.2016
0421/derive-2.5.24
Configuration files installed in:
/nix/store/izvyps3gi703y6ns4fz4m42hh1l7q9zw-derive-2.5.24/etc
No alex found
Using ar found on system at:
/nix/store/s0kpgl8a101lkymj599f5a04s4wflf5s-binutils-2.26-dev/bin/ar
No c2hs found
Using cpphs version 1.20.1 found on system at:
/nix/store/vxpa5hg25g21qqjy0pnh8hwv6vz9bh14-cpphs-1.20.1/bin/cpphs
Using gcc version 5.3.0 given by user at:
/nix/store/ix03iknfgyrx7421fppjdczd9r4sw7pz-gcc-wrapper-5.3.0/bin/gcc
Using ghc version 8.0.0.20160421 found on system at:
/nix/store/57zrq025ih51wf09zi7i03jnkr16957h-ghc-8.0.0.20160421/bin/ghc
Using ghc-pkg version 8.0.0.20160421 found on system at:
/nix/store/57zrq025ih51wf09zi7i03jnkr16957h-ghc-8.0.0.20160421/bin/ghc-pkg
No ghcjs found
No ghcjs-pkg found
No greencard found
Using haddock version 2.17.0 found on system at:
/nix/store/57zrq025ih51wf09zi7i03jnkr16957h-ghc-8.0.0.20160421/bin/haddock
No happy found
Using haskell-suite found on system at: haskell-suite-dummy-location
Using haskell-suite-pkg found on system at: haskell-suite-pkg-dummy-location
No hmake found
Using hpc version 0.67 found on system at:
/nix/store/57zrq025ih51wf09zi7i03jnkr16957h-ghc-8.0.0.20160421/bin/hpc
Using hsc2hs version 0.68 found on system at:
/nix/store/57zrq025ih51wf09zi7i03jnkr16957h-ghc-8.0.0.20160421/bin/hsc2hs
Using hscolour version 1.24 found on system at:
/nix/store/1dczsrvfp57p6rz1awyhq2qmdk2qjp17-hscolour-1.24/bin/HsColour
No jhc found
Using ld found on system at:
/nix/store/ix03iknfgyrx7421fppjdczd9r4sw7pz-gcc-wrapper-5.3.0/bin/ld
No lhc found
No lhc-pkg found
No pkg-config found
Using strip version 2.26 found on system at:
/nix/store/s0kpgl8a101lkymj599f5a04s4wflf5s-binutils-2.26-dev/bin/strip
Using tar found on system at:
/nix/store/acikdr9h8d0jmrjxfyyh6mnh8dznqv8a-gnutar-1.28/bin/tar
No uhc found
building
Building derive-2.5.24...
Preprocessing library derive-2.5.24...
[ 1 of 64] Compiling Language.Haskell.TH.Compat ( src/Language/Haskell/TH/Compat.hs, dist/build
/Language/Haskell/TH/Compat.o )
[ 2 of 64] Compiling Language.Haskell.TH.Data ( src/Language/Haskell/TH/Data.hs, dist/build/Lan
guage/Haskell/TH/Data.o )
[ 3 of 64] Compiling Language.Haskell.TH.ExpandSynonym ( src/Language/Haskell/TH/ExpandSynonym.
hs, dist/build/Language/Haskell/TH/ExpandSynonym.o )
[ 4 of 64] Compiling Language.Haskell.TH.Helper ( src/Language/Haskell/TH/Helper.hs, dist/build
/Language/Haskell/TH/Helper.o )

src/Language/Haskell/TH/Helper.hs:59:37: error:
    • Couldn't match expected type ‘Dec’
                  with actual type ‘[Dec] -> Dec’
    • Probable cause: ‘InstanceD’ is applied to too few arguments
      In the expression: InstanceD ctx hed defs
      In an equation for ‘instance_context’:
          instance_context req cls dat defs
            = InstanceD ctx hed defs
            where
                vrs = vars 't' (dataArity dat)
                hed = l1 cls (lK (dataName dat) vrs)
                ctx = [typeToPred $ l1 r v | r <- req, v <- vrs]

src/Language/Haskell/TH/Helper.hs:59:47: error:
    • Couldn't match expected type ‘Maybe Overlap’
                  with actual type ‘[Type]’
    • In the first argument of ‘InstanceD’, namely ‘ctx’
      In the expression: InstanceD ctx hed defs
      In an equation for ‘instance_context’:
          instance_context req cls dat defs
            = InstanceD ctx hed defs
            where
                vrs = vars 't' (dataArity dat)
                hed = l1 cls (lK (dataName dat) vrs)
                ctx = [typeToPred $ l1 r v | r <- req, v <- vrs]

src/Language/Haskell/TH/Helper.hs:59:55: error:
    • Couldn't match expected type ‘Type’ with actual type ‘[Dec]’
    • In the third argument of ‘InstanceD’, namely ‘defs’
      In the expression: InstanceD ctx hed defs
      In an equation for ‘instance_context’:
          instance_context req cls dat defs
            = InstanceD ctx hed defs
            where
                vrs = vars 't' (dataArity dat)
                hed = l1 cls (lK (dataName dat) vrs)
                ctx = [typeToPred $ l1 r v | r <- req, v <- vrs]

src/Language/Haskell/TH/Helper.hs:63:29: error:
    • Couldn't match type ‘[Pred]’ with ‘Type’
      Expected type: Type
        Actual type: Cxt
    • In the second argument of ‘($)’, namely ‘l1 r v’
      In the expression: typeToPred $ l1 r v
      In the expression: [typeToPred $ l1 r v | r <- req, v <- vrs]

src/Language/Haskell/TH/Helper.hs:73:43: error:
    • Couldn't match expected type ‘Dec’
                  with actual type ‘[Dec] -> Dec’
    • Probable cause: ‘InstanceD’ is applied to too few arguments
      In the expression: InstanceD ctx hed defs
      In the expression: [InstanceD ctx hed defs]
      In an equation for ‘generic_instance’:
          generic_instance cls dat ctxTypes defs
            = [InstanceD ctx hed defs]
            where
                vrs = vars 't' (dataArity dat)
                hed = l1 cls (lK (dataName dat) vrs)
                ctx = map (typeToPred . l1 cls) ctxTypes

src/Language/Haskell/TH/Helper.hs:73:53: error:
    • Couldn't match expected type ‘Maybe Overlap’
                  with actual type ‘[Type]’
    • In the first argument of ‘InstanceD’, namely ‘ctx’
      In the expression: InstanceD ctx hed defs
      In the expression: [InstanceD ctx hed defs]

src/Language/Haskell/TH/Helper.hs:73:61: error:
    • Couldn't match expected type ‘Type’ with actual type ‘[Dec]’
    • In the third argument of ‘InstanceD’, namely ‘defs’
      In the expression: InstanceD ctx hed defs
      In the expression: [InstanceD ctx hed defs]
note: keeping build directory ‘/tmp/nix-build-derive-2.5.24.drv-4’
builder for ‘/nix/store/ripjal00hdc9xf9dzanhrcry9g0rj94s-derive-2.5.24.drv’ failed with exit code 1
error: build of ‘/nix/store/ripjal00hdc9xf9dzanhrcry9g0rj94s-derive-2.5.24.drv’ failed

[ndmitchell]

Thanks for the heads up @deepfire - seems there were some last minute further changes to template haskell after RC2. Hopefully the work required to fix it up should be small...

[ndmitchell]

Fixed, just one small change to InstanceD to add an extra field.

Annoyingly, I also get a stupid warning from the stupid pattern match checker in GHC 8.0 saying "hmm, yeah, dude, didn't manage it - whateves". Since someone decided that should be a warning in my code I've had to turn off warnings as errors on that module.