With that in mind, and considering a cloud build system where "all direct
inputs and direct outputs must be declared"
But I question that assumption. As I mentioned, with GHC at least, the if a
deep dependency changes then one of the shallow dependencies will change. So I
claim that even for cloud build it should be enough to depend only on shallow
dependencies.
This is only true because GHC offers this guarantee. We’d need to be sure that
every deep dependency was either ‘needed’ or was reflected in the contents
(perhaps via a fingerprint) another ‘needed’ thing.
Simon
From: ghc-devs <ghc-devs-boun...@haskell.org> On Behalf Of David Eichmann
Sent: 27 March 2019 17:12
To: Andrey Mokhov <andrey.mok...@newcastle.ac.uk>; Neil Mitchell
<ndmitch...@gmail.com>
Cc: GHC developers <ghc-devs@haskell.org>
Subject: Re: Hadrian Transitive Dependencies
Hello,
To reiterate some definitions consider this scenario:
* A.hs imports B.hs and B.hs imports C.hs
* `ghc -M A.hs` reports that A.o depends on: A.hs, B.hi
* `ghc -c A.hs` produces A.o and accesses A.hs, B.hi, and C.hi
There seems to be some confusion about the term "Direct Dependency" I'll use
these definitions:
"Shallow Dependency": With respect to a haskell object file X.o, the shallow
dependencies are the source file X.hs and interface files Y.hi for all modules
Y imported by X.
* These are the dependencies of X.o as reported by `ghc -M X.hs`
* In the above scenario:
* A.o depends on: A.hs, B.hi
"Deep Dependency": With respect to a haskell object file X.o, the deep
dependencies are all hi files required by ghc to build X.o excluding direct
dependencies:
* This is a subset of modules transitively imported by X
* These dependencies are NOT reported by `ghc -M X.hs`
"Direct Dependency": if the command to create file X accesses file Y, then X
directly depends on Y (= Y is a direct dependency of X).
* In the above scenario:
* A.o directly depends on: A.hs, B.hi, and C.hi
* SPJ noted that .hi files list direct dependencies.
* The direct dependencies of a haskell object file is the union of its
shallow and deep dependencies.
"Direct Output": All files created by a rule.
With that in mind, and considering a cloud build system where "all direct
inputs and direct outputs must be declared" (where this agrees with the
definitions above) can we do the following for the build rule of a haskell
object file X.o?
1. `need` the shallow dependencies as reported by `ghc -M`. This guarantees
that all shallow and deep dependencies (i.e. all direct dependencies) are built.
2. build X.o and X.hi
3. Inspect X.hi to derive the direct dependencies (and hence deep
dependencies)
4. `needed` the deep dependencies
Is there already an easy way to inspect *.hi files in this way? Is this use of
`needed` valid?
- David E
On 3/27/19 3:05 PM, Andrey Mokhov wrote:
Hi David,
We had a discussion about this with Neil some time ago, and I think we had the
following list of progressively more complex invariants for different types of
build systems:
* Non-cloud build systems: *all direct inputs must be declared*. If you
miss a direct input dependency then a build may complete successfully but with
an incorrect result.
* Cloud build systems: *all direct inputs and direct outputs must be
declared*. If you miss a direct output then a build may fail because the cloud
will not be able to restore the corresponding output.
* Cloud build systems with shallow (deferred) materialisation of build
artefacts: *all transitive inputs and direct outputs must be declared*. Let’s
say you’d like to download the resulting GHC binary directly, without
materialising any intermediate artefacts. Then you’ll need to know GHC’s
ultimate transitive inputs.
I think for now we are really keen to make Hadrian a cloud build system, but
whether shallow builds are valuable enough is not clear. Maybe not. Therefore,
I’d say we don’t need to track transitive inputs right now. Furthermore, if we
were to track all transitive inputs, we would lose the desirable early cutoff
property, which prevents rebuilding after adding a comment in a file on which a
lot of other files transitively depend on.
Having said that, if we really access a file during compilation, then I think
it is *not* a transitive dependency by definition! Any file which is accessed
during a build rule is a direct dependency.
> 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!
So, here I’m confused. If we read a file A when compiling a file B, then it’s
by definition a direct dependency. Perhaps we just read too much? Maybe the
solution is to switch to fine-grained `ghc -M` mode, to analyse import
dependencies for a single module instead of doing it transitively, which I
believe was discussed in a ticket some time ago? I can’t find this ticket, but
I think Alp was looking into it at some point. Alp: do you remember it?
Thank you for all your work on Hadrian!
Cheers,
Andrey
From: David Eichmann [mailto:dav...@well-typed.com]
Sent: 27 March 2019 12:54
To: Neil Mitchell <ndmitch...@gmail.com><mailto:ndmitch...@gmail.com>; Andrey
Mokhov <andrey.mok...@newcastle.ac.uk><mailto:andrey.mok...@newcastle.ac.uk>;
GHC developers <ghc-devs@haskell.org><mailto:ghc-devs@haskell.org>
Subject: Hadrian Transitive Dependencies
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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2Fissues%2F16295&data=02%7C01%7Csimonpj%40microsoft.com%7Cbd87a25e08f441fe763d08d6b2d76b25%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636893035618959820&sdata=BomxywLkHm7mriTubSnCql6YJDJBR96K1tQbskKBMn4%3D&reserved=0>.
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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2Fissues%2F16400%23note_188901&data=02%7C01%7Csimonpj%40microsoft.com%7Cbd87a25e08f441fe763d08d6b2d76b25%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636893035618969820&sdata=Kmnd%2B8%2FATQBw0AfCTvvl7oix5syXbPAeV7h473t8H7E%3D&reserved=0>
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<https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.well-typed.com&data=02%7C01%7Csimonpj%40microsoft.com%7Cbd87a25e08f441fe763d08d6b2d76b25%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636893035618979828&sdata=ZUSCHtfKiOsTYbS%2Bo%2FAuhSuXwtM5TKnzVPubJjZd6RI%3D&reserved=0>
Registered in England & Wales, OC335890
118 Wymering Mansions, Wymering Road, London W9 2NF, England
--
David Eichmann, Haskell Consultant
Well-Typed LLP,
http://www.well-typed.com<https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.well-typed.com&data=02%7C01%7Csimonpj%40microsoft.com%7Cbd87a25e08f441fe763d08d6b2d76b25%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636893035618989837&sdata=QxSKBt9C1rO8AwS0C8%2FIPhK43naICuuJ8ebdIzaudnQ%3D&reserved=0>
Registered in England & Wales, OC335890
118 Wymering Mansions, Wymering Road, London W9 2NF, England
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