virtual-modules section: docs

[ciez]

Could anyone hint / share links to a description of .cabal file virtual-modules section?

The docs show but a placeholder:
https://cabal.readthedocs.io/en/3.4/cabal-package.html?highlight=virtual-modules#pkg-field-virtual-modules

[Mikolaj]

That's just a flat list of modules, just as exposed-modules.

Some snippets from git grep -30 virtual-modules:

Cabal/ChangeLog.md: * Added virtual-modules field, to allow modules that are not built
Cabal/ChangeLog.md- but registered (#4875).

doc/cabal-package.rst:.. pkg-field:: virtual-modules: identifier list
doc/cabal-package.rst- :since: 2.2
doc/cabal-package.rst-
doc/cabal-package.rst- A list of virtual modules provided by this package. Virtual modules
doc/cabal-package.rst- are modules without a source file. See for example the GHC.Prim
doc/cabal-package.rst- module from the ghc-prim package. Modules listed here will not be
doc/cabal-package.rst- built, but still end up in the list of exposed-modules in the
doc/cabal-package.rst- installed package info when the package is registered in the package
doc/cabal-package.rst- database.

[phadej]

TL;DR you don't need virtual-modules (except if you are GHC developer). It's a feature solely for GHC need: GHC.Prim module in ghc-prim doesn't really exist as a source. GHC just knows it.

[ciez]

Cheers Mikolaj, Oleg.

So for all practical purposes could this file be added in ghc-prim/GHC folder to the same effect:
Prim.hs
?

Background:

GHC.Prim is imported in a few places. A custom (editor) name resolver does not find GHC.Prim when viewing / editing GHC sources.

[phadej]

@ciez no. That would be a different module. It also may confuse build system, if source existed. GHC.Prim contains the primops, which are hard-wired into compiler. I think things (like costom name resolver) just have to know about that corner case, i.e. that virtual-modules (which is only one) doesn't exist. E.g. the module finder in GHC itself has following code:

   -- special case for GHC.Prim; we won't find it in the filesystem.
   -- This is important only when compiling the base package (where GHC.Prim
   -- is a home module).
   if mod `installedModuleEq` gHC_PRIM
         then return (InstalledFound (error "GHC.Prim ModLocation") mod)
         else searchPathExts home_path mod exts

[ciez]

So in this particular case, what Haskell (apart from C, C++) symbols does GHC.Prim export?

All the symbols exported by
GHC.CString,
GHC.Classes,
GHC.Debug,
GHC.IntWord64,
GHC.Magic,
GHC.Prim.Ext,
GHC.Tuple,
GHC.Types
or ..?

[phadej]

The haddocks are correct. (EDIT: They are magically generated, that's why they don't exist for ghc-prim-0.7 on hackage). The primitive types like Int# and operations on them like (+#)

[phadej]

I found this: https://downloads.haskell.org/ghc/9.2.1-rc1/docs/html/libraries/ghc-prim-0.8.0/src/GHC.Prim.html

[ciez]

Cheers Oleg!
This is just what I was looking for.

Appreciate this.