RFE: allow (ghc with) missing haddock

[juhp]

General summary

I sometimes build ghc locally without haddock to save time.
It would be nice if it was possible to use stack with such a ghc.

Steps to reproduce

1. Remove (or "disable") haddock (or switch to a ghc without haddock enabled)
2. Run command stack install.

Expected

stack to ignore missing haddock binary since it is not needed for stack install.

Actual

$ stack-2.9.3 install
Trouble loading CompilerPaths cache: CompilerFileMetadataMismatch
Error: [S-2476]
Found an invalid compiler at "/var/home/petersen/.stack/programs/x86_64-linux/ghc-tinfo6-8.10.7/bin/ghc": Error: [S-4764]
Could not find any of: ["/var/home/petersen/.stack/programs/x86_64-linux/ghc-tinfo6-8.10.7/bin/haddock","/var/home/petersen/.stack/programs/x86_64-linux/ghc-tinfo6-8.10.7/bin/haddock-ghc"]

Stack version

$ stack --version
Version 2.9.3, Git revision 6cf638947a863f49857f9cfbf72a38a48b183e7e x86_64 hpack-0.35.1

Method of installation

• Official binary, downloaded via haskellstack.org or from Stack's repository (via stack upgrade)

Platform

Fedora Linux

[mpilgrem]

@juhp, thanks for reporting. Some notes for my own use:

Stack does not consider an available sandboxed GHC to be valid, if it is missing both the executables haddock and haddock-ghc. The data constructor for type Stack.Types.Config.CompilerPaths assumes that there will be an absolute path to a Haddock executable.

How could a sandboxed GHC ever be missing a Haddock executable? Is it that there are Hadrian 'flavours' that 'leave out' the Haddock executable? https://docs.haskellstack.org/en/stable/yaml_configuration/#building-ghc-from-source

However, if a user commands stack build --no-haddock (--no-haddock being the default) does Stack have any need for the Haddock executable?

[mpilgrem]

@juhp, for my education, how do you create a sandboxed GHC that is missing a Haddock executable (as opposed to going to an existing sandboxed GHC and removing its Haddock functionality)? Or is this not limited to Stack-supplied GHC?

[juhp]

First I just want to state that this issue is obviously a corner-case.

Is it that there are Hadrian 'flavours' that 'leave out' the Haddock executable?

You can hadrian build ghc without haddock(s): using --docs=no-haddocks.

However, if a user commands stack build --no-haddock (--no-haddock being the default) does Stack have any need for the Haddock executable?

I suppose not: that was mostly my point: why is stack insisting on (ie always checking for) haddock when probably 90% of user invocations don't need it. :-)

@juhp, for my education, how do you create a sandboxed GHC that is missing a Haddock executable (as opposed to going to an existing sandboxed GHC and removing its Haddock functionality)?

One probably can't normally with stack?