Build failure -- missing dependency? Help!

[Simon Peyton Jones]

Thanks Sylvain
So we should add a similar fake import into libraries/base/GHC/Exception/Type.hs-boot. I will open a MR.
Thank you! Don't forget to comment it - especially because it is fake.
Make build system doesn't respect package dependencies, only module dependencies (afaik)
Does Hadrian suffer from this malady too?  Are the fake imports needed? Or can we sweep them away when we sweep away make?
Simon

From: ghc-devs <ghc-devs-bounces at haskell.org> On Behalf Of Sylvain Henry
Sent: 15 March 2021 08:30
To: ghc-devs at haskell.org
Subject: Re: Build failure -- missing dependency? Help!


Hi Simon,

The issue is that:
1. Make build system doesn't respect package dependencies, only module dependencies (afaik)
2. The build system isn't aware that most modules implicitly depend on GHC.Num.Integer/Natural (to desugar Integer/Natural literals)

That's why we have several fake imports in `base` that look like:

> import GHC.Num.Integer () -- See Note [Depend on GHC.Num.Integer] in GHC.Base

Note [Depend on GHC.Num.Integer]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Integer type is special because GHC.Iface.Tidy uses constructors in
GHC.Num.Integer to construct Integer literal values. Currently it reads the
interface file whether or not the current module *has* any Integer literals, so
it's important that GHC.Num.Integer is compiled before any other module.

(There's a hack in GHC to disable this for packages ghc-prim and ghc-bignum
which aren't allowed to contain any Integer literals.)

Likewise we implicitly need Integer when deriving things like Eq instances.

The danger is that if the build system doesn't know about the dependency
on Integer, it'll compile some base module before GHC.Num.Integer,
resulting in:
  Failed to load interface for 'GHC.Num.Integer'
    There are files missing in the 'ghc-bignum' package,

Bottom line: we make GHC.Base depend on GHC.Num.Integer; and everything
else either depends on GHC.Base, or does not have NoImplicitPrelude
(and hence depends on Prelude).

Note: this is only a problem with the make-based build system. Hadrian doesn't
seem to interleave compilation of modules from separate packages and respects
the dependency between `base` and `ghc-bignum`.

So we should add a similar fake import into libraries/base/GHC/Exception/Type.hs-boot. I will open a MR.

Sylvain




On 14/03/2021 21:53, Simon Peyton Jones via ghc-devs wrote:
I'm getting this (with 'sh validate -legacy').  Oddly

  1.  It does not happen on HEAD
  2.  It does happen on wip/T19495, a tiny patch with one innocuous change to GHC.Tc.Gen.HsType
I can't see how my patch could possible cause "missing files" in ghc-bignum!
I'm guessing that there is a missing dependency that someone doesn't show up in master, but does in my branch, randomly.
There's something funny about ghc-bignum; it doesn't seem to be a regular library
Can anyone help?
Thanks
Simon

"inplace/bin/ghc-stage1" -hisuf hi -osuf  o -hcsuf hc -static  -O -H64m -Wall -fllvm-fill-undef-with-garbage    -Werror    -this-unit-id base-4.16.0.0 -hide-all-packages -package-env - -i -ilibraries/base/. -ilibraries/base/dist-install/build -Ilibraries/base/dist-install/build -ilibraries/base/dist-install/build/./autogen -Ilibraries/base/dist-install/build/./autogen -Ilibraries/base/include -Ilibraries/base/dist-install/build/include    -optP-include -optPlibraries/base/dist-install/build/./autogen/cabal_macros.h -package-id ghc-bignum-1.0 -package-id ghc-prim-0.8.0 -package-id rts -this-unit-id base -Wcompat -Wnoncanonical-monad-instances -XHaskell2010 -O -dcore-lint -ticky -Wwarn  -no-user-package-db -rtsopts  -Wno-trustworthy-safe -Wno-deprecated-flags     -Wnoncanonical-monad-instances  -outputdir libraries/base/dist-install/build  -dynamic-too -c libraries/base/./GHC/Exception/Type.hs-boot -o libraries/base/dist-install/build/GHC/Exception/Type.o-boot -dyno libraries/base/dist-install/build/GHC/Exception/Type.dyn_o-boot

Failed to load interface for 'GHC.Num.Integer'

There are files missing in the 'ghc-bignum' package,

try running 'ghc-pkg check'.

Use -v (or `:set -v` in ghci) to see a list of the files searched for.

make[1]: *** [libraries/base/ghc.mk:4: libraries/base/dist-install/build/GHC/Exception/Type.o-boot] Error 1

make[1]: *** Waiting for unfinished jobs....



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