v2-cabal: Don't rebuild dependencies when `-O0` or `-fno-code` is supplied as `--ghc-options`

[andreasabel]

It seems that cabal v2-build wants to rebuild all dependencies when I add --ghc-options=-O0 or ...=-fno-code to e.g. just check compilability after a change.

I don't understand the rationale behind this behavior.

Is there a workaround? I'd like to alternate compilation between -fno-code (for just type-checking), -O0 (for running a first few test), and -O1 (for thorough testing with a large testsuite).

See also #2442 and #1176.

Example see #1176 (comment).

[phadej]

What's wrong with cabal build -O0?

[andreasabel]

What's wrong with cabal build -O0?

Ah, great, this works!

So this means something like cabal build --no-code would remain as feature request (#1176).

[fgaz]

Subsumed by #3579?

edit: actually this should be possible already by specifying the option for every local package, like in #3579 (comment), just a bit tedious. @andreasabel does that work for you?

[andreasabel]

@andreasabel does that work for you?

Not sure, I how would that look like?
I want something convenient and accessible, ideally as simple as passing the option -O0 to cabal.

For comparison, with v1-cabal it is:

cabal v1-build --builddir=dist-no-code --ghc-options=-fno-code --ghc-options=-fwrite-interface

[Mikolaj]

@andreasabel: any news here?

[fgaz]

Not sure, I how would that look like?

Like the comment I mentioned ( #3579 (comment) ), so

local-package-1
  ghc-options: -fno-code

local-package-2
  ghc-options: -fno-code

Not that convenient but it works. If you put that configuration in another cabal.project file you could switch between the two from the command line.

Should we close this in favour of #1176 and #3579?

[andreasabel]

This does not work, or maybe something is missing. Can you give full instructions?
E.g. I am trying with cabal.project.tc

packages: .

builddir: dist-tc
ghc-options: -fno-code -fwrite-interface

cabal --project-file=cabal.project.tc build

This reports, before starting the build:

Warning: .../cabal.project.tc: Unrecognized field 'ghc-options' on line 4

Further, the builddir:dist-tc seems to be silently dropped, at least no subfolder named dist-tc was created.

[fgaz]

assuming my_package is the name of the package referred as .:

packages: .

package my_package
    ghc-options: -fno-code -fwrite-interface

[fgaz]

Further, the builddir:dist-tc seems to be silently dropped, at least no subfolder named dist-tc was created.

This is documented: https://cabal.readthedocs.io/en/3.4/cabal-project.html#cmdoption-builddir

Though I don't know why it can't be specified in cabal.project. Probably caching reasons. I think there is a ticket somewhere discussing it

Making it give a warning or error would be nice

[andreasabel]

This is documented: cabal.readthedocs.io/en/3.4/cabal-project.html#cmdoption-builddir

Thanks.
(Yet I'd expect a warning that this is not understood, rather silently dropping it.)

But to the original issue: With

packages: .

package Agda
  ghc-options: -fno-code -fwrite-interface

and

cabal --project-file=cabal.project.tc --builddir=dist-tc build

It does indeed work. Fantastic!

...
[404 of 404] Compiling Agda.Main        ( src/full/Agda/Main.hs, nothing, dist-tc/build/x86_64-osx/ghc-9.2.1/Agda-2.6.3/build/Agda/Main.dyn_o )
ar: dist-tc/build/x86_64-osx/ghc-9.2.1/Agda-2.6.3/build/Agda/Auto/Auto.o: No such file or directory
...

There are 404 errors about missing .o files, but this was already the case in v1-cabal.