Output hadrian build data for cabal-helper tool support

As a step in the direction of adding tool support for ghc development we can output some meta data from Hadrian to better support the cabal-helper tool. Proposed changes:

1. Add a <ghc-root>/cabal.helper file that points to the 3 stage build directories under the default Hadrian build dir: _build.
2. Add a "--cabal-helper" command line option to Hadrian that enables this output.
3. Output <build-root>/stage<x>/build.helper in JSON format containing per package:

• .cabal file path relative to <ghc-root> (achieved by prefixing paths with $PROJECTDIR) e.g $PROJECTDIR/libraries/binary/binary.cabal
• source path e.g. $PROJECTDIR/libraries/binary/binary.cabal
• Build "dist directory", which is the directory containing the setup-config file generated by cabal on build. this is a relative path e.g. libraries/binary/setup-config

## TODO

• decide on the naming of files

## Implementation

• See:

  * Packages.ghcPackages

  * Hadrian.Package.pkgCabalFile

Trac metadata

Trac field	Value
Version	8.6.2
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Build System (Hadrian)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	DanielG
Operating system
Architecture

changed milestone to %8.6.3

changed weight to 5

added Tfeature request Trac import hadrian labels

Ticket retargeted after milestone closed

added Pnormal label

I don't think there is much sense in implement cabal-helper support at this point. However, hie-bios support would be quite reasonable. If fact, didn't you implement just this, @mpickering?

Indeed he did. See https://gitlab.haskell.org/ghc/ghc/blob/4898df1cc25132dc9e2599d4fa4e1bbc9423cda5/hadrian/hie-bios.

closed