Hadrian Transitive Dependencies

Wed Mar 27 11:53:43 UTC 2019

Hello Shake/Hadrian contributors and the like,

Recently I've been putting Hadrian's fsatrace linting feature to good 
use, tracking down missing dependencies in Hadrian. Ultimately, we want 
to use shake's cloud build / shared cache feature and ensure it works 
across CI builds. Unfortunately the feature isn't working smoothly with 
Hadrian: see #16295 <https://gitlab.haskell.org/ghc/ghc/issues/16295>. 
This is very desirable to improve CI build times. It is my understanding 
that in order to get caching to work:

1. All accessed files must declared with `need` AND
2. All created files must be declared with `produces` (or be the target 
of the build rule)

Is my understanding correct? Or is there a weaker condition (perhaps 
only 2 is necessary)?

If I'm correct, this amounts to fixing all fsatrace lint errors. See 
here <https://gitlab.haskell.org/ghc/ghc/issues/16400#note_188901> for a 
breakdown of lint errors / missing dependencies. A large portion of 
these are Haskell interface files (i.e. *.hi files). Before building a 
Haskell object file, dependencies are discovered via `ghc` using the 
`-M  -include-pkg-deps` options. Unfortunately, shake's fsatrace linting 
complains about other *.hi files being accessed! For example when 
building `stage1/libraries/mtl/build/Control/Monad/RWS/Class.o` we get 
the following dependencies from ghc:

_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : libraries/mtl/Control/Monad/RWS/Class.hs
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/lib/../lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/Prelude.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/lib/../lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/Data/Monoid.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/lib/../lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/RWS/Strict.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/lib/../lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/RWS/Lazy.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/lib/../lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Identity.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/lib/../lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Maybe.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/lib/../lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Except.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/lib/../lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Error.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/lib/../lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Class.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/libraries/mtl/build/Control/Monad/Writer/Class.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/libraries/mtl/build/Control/Monad/State/Class.hi
_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/libraries/mtl/build/Control/Monad/Reader/Class.hi

And shake complains of the following missing deps:

_build/stage0/bin/ghc -Wall -hisuf hi -osuf o -hcsuf hc -static -hide-all-packages -no-user-package-db '-package-db _build/stage1/lib/package.conf.d' '-this-unit-id mtl-2.2.2' '-package-id base-4.13.0.0' '-package-id transformers-0.5.5.0' -i -i_build/stage1/libraries/mtl/build -i_build/stage1/libraries/mtl/build/autogen -ilibraries/mtl/. -Iincludes -I_build/generated -I_build/stage1/libraries/mtl/build -I/home/david/ghc/_build/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/include -I/home/david/ghc/_build/stage1/lib/x86_64-linux-ghc-8.9.20190325/integer-gmp-1.0.2.0/include -I/home/david/ghc/_build/stage1/lib/x86_64-linux-ghc-8.9.20190325/rts-1.0/include -I_build/generated -optc-I_build/generated -optP-include -optP_build/stage1/libraries/mtl/build/autogen/cabal_macros.h -outputdir _build/stage1/libraries/mtl/build -Wnoncanonical-monad-instances -optc-Werror=unused-but-set-variable -optc-Wno-error=inline -c libraries/mtl/Control/Monad/RWS/Class.hs -o _build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o -O2 -H32m -Wall -fno-warn-unused-imports -fno-warn-warnings-deprecations -Wcompat -Wnoncanonical-monad-instances -Wnoncanonical-monadfail-instances -XHaskell2010 -XSafe -ghcversion-file=/home/david/MEGA/File_Dump/Well-Typed/GHC/_nosync_git/ghc/_build/generated/ghcversion.h -Wno-deprecated-flags
Lint checking error - _build/HEAD_default/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o - 22 values were used but not depended upon:
   Used:  _build/HEAD_default/stage0/lib/settings
   Used:  _build/HEAD_default/stage0/lib/platformConstants
   Used:  _build/HEAD_default/stage0/lib/llvm-targets
   Used:  _build/HEAD_default/stage0/lib/llvm-passes
   Used:  _build/HEAD_default/stage0/lib/package.conf.d/package.cache
   Used:  _build/HEAD_default/stage1/lib/package.conf.d/package.cache
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/Float.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/Base.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/ghc-prim-0.5.3/GHC/Types.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/Maybe.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Writer/Lazy.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Writer/Strict.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/State/Lazy.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/State/Strict.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Reader.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/List.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Cont.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/ghc-prim-0.5.3/GHC/Tuple.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/IO/Exception.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/integer-gmp-1.0.2.0/GHC/Integer/Type.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/Data/Either.hi
   Used:  _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/Natural.hi

GHC is reading *.hi files that are not reported as dependencies by `ghc 
-M  -include-pkg-deps`. This is because they are not direct, but 
/transitive/ dependencies! How do we fix these lint errors (again with 
the goal of using shakes shared cache feature)? Some ideas:

* Wildly over approximate dependencies. This may be easier to implement 
but cause unneeded recompilation (when a false dependency changes). Either:
     * `need` all dependent packages' interface files recursively as 
well as transitive dependencies reported by `ghc -M -include-pkg-deps` 
within the current package. OR
     * OR `need` all transitive dependencies reported by `ghc -M 
-include-pkg-deps`. This will likely result in fewer dependencies but 
requires a bit more work in recovering dependent packages' dependency 
graphs.
* Perhaps transitive dependencies are not important for shared caching 
to work. Change shakes linting feature to allow (untracked?) transitive 
dependencies to be accessed.

Feed back would be greatly appreciated.

David Eichmann

-- 
David Eichmann, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com

Registered in England & Wales, OC335890
118 Wymering Mansions, Wymering Road, London W9 2NF, England

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-devs/attachments/20190327/32af95e0/attachment.html>