Missing IsString instance with debug flags enabled

[kleinreact]

Compiling Agda 2.6.4.1 on GHC 9.4.5 with the cabal flags debug, debug-parsing, and debug-serialisation enabled leads to the following erros:

src/full/Agda/Main.hs:291:5: error:
    • No instance for (Data.String.IsString (t0 -> [a0] -> [[Char]]))
        arising from the literal ‘"debug-parsing: enable printing grammars for operator parsing via '-v scope.grammar:10'"’
        (maybe you haven't applied a function to enough arguments?)
    • In the second argument of ‘(:)’, namely
        ‘"debug-parsing: enable printing grammars for operator parsing via '-v scope.grammar:10'"
           "debug-serialisation: extra debug info during serialisation into '.agdai' files"
           []’
      In the expression:
        "debug: enable debug printing ('-v' verbosity flags)"
          : "debug-parsing: enable printing grammars for operator parsing via '-v scope.grammar:10'"
              "debug-serialisation: extra debug info during serialisation into '.agdai' files"
              []
      In an equation for ‘flags’:
          flags
            = "debug: enable debug printing ('-v' verbosity flags)"
                : "debug-parsing: enable printing grammars for operator parsing via '-v scope.grammar:10'"
                    "debug-serialisation: extra debug info during serialisation into '.agdai' files"
                    []
    |
291 |     "debug-parsing: enable printing grammars for operator parsing via '-v scope.grammar:10'"
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/full/Agda/Main.hs:294:5: error:
    • Ambiguous type variable ‘t0’ arising from the literal ‘"debug-serialisation: extra debug info during serialisation into '.agdai' files"’
      prevents the constraint ‘(Data.String.IsString
                                  t0)’ from being solved.
      Probable fix: use a type annotation to specify what ‘t0’ should be.
      Potentially matching instances:
        instance (Data.String.IsString a, MonadIO m) =>
                 Data.String.IsString (TCMT m a)
          -- Defined at src/full/Agda/TypeChecking/Monad/Base.hs:5350:10
        instance (a ~ Char) => Data.String.IsString [a]
          -- Defined in ‘Data.String’
        ...plus 33 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the first argument of ‘"debug-parsing: enable printing grammars for operator parsing via '-v scope.grammar:10'"’, namely
        ‘"debug-serialisation: extra debug info during serialisation into '.agdai' files"’
      In the second argument of ‘(:)’, namely
        ‘"debug-parsing: enable printing grammars for operator parsing via '-v scope.grammar:10'"
           "debug-serialisation: extra debug info during serialisation into '.agdai' files"
           []’
      In the expression:
        "debug: enable debug printing ('-v' verbosity flags)"
          : "debug-parsing: enable printing grammars for operator parsing via '-v scope.grammar:10'"
              "debug-serialisation: extra debug info during serialisation into '.agdai' files"
              []
    |
294 |     "debug-serialisation: extra debug info during serialisation into '.agdai' files"
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[andreasabel]

@UlfNorell : This issue points at gaps in our build matrix. Could you please add a configuration that would have exposed this issue?

agda/src/github/workflows/cabal.yml

Lines 58 to 83 in a445e3b

	include:
	## Latest GHC, special builds
	# Linux, without tests but with doctest
	- os: ubuntu-22.04
	description: Linux doctest
	ghc-ver: '9.8.1'
	# Can't leave cabal-flags empty here lest it becomes the default value.
	cabal-flags: '--disable-tests'
	doctest: true
	# Linux, without -f enable-cluster-counting but with -f debug
	- os: ubuntu-22.04
	description: Linux debug
	ghc-ver: '9.8.1'
	cabal-flags: '--enable-tests -f debug'
	# Linux, with containers-0.7 and everything
	- os: ubuntu-22.04
	description: Linux containers 0.7
	ghc-ver: '9.8.1'
	## Andreas, 2023-09-28: Test containers-0.7 here which has breaking changes.
	## Note: -c 'containers >= 0.7' with single quotes does not get communicated properly.
	## (The single quotes stay, and "-c 'containers" is an option parse error for cabal.)
	cabal-flags: |
	--enable-tests -f enable-cluster-counting -f debug -c containers>=0.7 --allow-newer=containers

[UlfNorell]

I'll leave that to someone more familiar with the CI system. The test to add is compiling with all the debug flags turned on (-fdebug -fdebug-parsing -fdebug-serialisation).

[andreasabel]

I'll leave that to someone more familiar with the CI system.

Could be your entry point into CI...

I just realized that the released 2.6.4.1 has this build problem while working on relaxing its ansi-terminal constraint.
I guess this calls for a patch release 2.6.4.2.

[UlfNorell]

I wouldn't worry too much about this particular issue. -fdebug-parsing and -fdebug-serialisation are extremely niche flags that you only turn on if you are working on the operator parser or serialiser, and in that case you can fix any problems as you find them. I would argue it's not worth spending CI time or effort pushing out a hotfix release for this.

[andreasabel]

I don't want the latest release to have broken build paths.