Reading this certainly motivates me to push for a better design of the
respective boundaries of GHC and cabal. Removing magic from GHC that it
uses to compensate for the absence of cabal or other build system would
certainly help using it for simpler use-cases.
Le 10/07/2024 à 11:53, Oleg Grenrus a écrit :
On 10.7.2024 11.27, Simon Peyton Jones wrote:
I wonder if there is an articulate writeup of Cabal's mental model.
Sadly, i'm not aware of any. I'm also afraid, that Duncan's (who made
initial v2-setup), Herbert's (who pushed v2 over the line) and mine
models differ at least slightly.
The
https://well-typed.com/blog/2015/01/how-we-might-abolish-cabal-hell-part-2/
is Duncan's view from 2015.
A side comment, we really should rename either the Cabal-the-library
or cabal-install. Because I'm sure you are asking about mental model
behind cabal-install v2-build, as "nothing" has changed in
Cabal-the-library for a decade.
The idea is that cabal-install v2-build installs everything into
single global store, and gives consistent views to that store. In
practice the global store is unusable directly, as a whole it may not
be consistent nor unambiguous (see e.g.
https://gitlab.haskell.org/ghc/ghc/-/issues/24823 for funny
side-effects of that, you may have dozens of installed units in the
package db with the same package name and version).
e.g. What is an environment file?
Essentially it's a set of `-package-db` and `-package-id` flags.
In other words, environment files are (specialized) response-files
which ghc (tool, or lib) may pick up automatically.
They are a way to encode a view into cabal's store (but technically
there is no reason they cannot be used to give a view into stack's
snapshot package databases too)
Why can't my GHC find Prelude?
Probably because there is -hide-all-packages, -clear-package-db (or
both); without -package-db and -package-id for base (a package with
module Prelude).
If you invoke plain ghc, what packages does it "see"?
It depends on the state you have. This is complicated (use
cabal-install). If you have a default or local environment file, ghc
will use those. If there aren't it will use a global package db.
To be honest, I'm not so sure what GHC does by default. I'm mostly
familiar with programmatic execution, which often starts with
`-clear-package-db`, `-hide-all-packages` etc to clear all the
implicit stuff GHC may do.
- Oleg
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