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<p>Hello,</p>
<p>To reiterate some definitions consider this scenario:</p>
<ul>
<li>A.hs imports B.hs and B.hs imports C.hs</li>
<li>`ghc -M A.hs` reports that A.o depends on: A.hs, B.hi</li>
<li>`ghc -c A.hs` produces A.o and accesses A.hs, B.hi, and C.hi</li>
</ul>
<p>There seems to be some confusion about the term "Direct
Dependency" I'll use these definitions:</p>
<p>"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.</p>
<ul>
<li>These are the dependencies of X.o as reported by `ghc -M X.hs`</li>
<li>In the above scenario:</li>
<ul>
<li>A.o depends on: A.hs, B.hi</li>
</ul>
</ul>
<p>"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:</p>
<ul>
<li>This is a subset of modules transitively imported by X</li>
<li>These dependencies are NOT reported by `ghc -M X.hs`</li>
</ul>
<p>"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).</p>
<ul>
<li>In the above scenario:</li>
<ul>
<li>A.o directly depends on: A.hs, B.hi, and C.hi</li>
</ul>
<li>SPJ noted that .hi files list direct dependencies.</li>
<li>The direct dependencies of a haskell object file is the union
of its shallow and deep dependencies.</li>
</ul>
<p>"Direct Output": All files created by a rule.<br>
</p>
<p>With that in mind, and considering a cloud build system where "<span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><b>all
direct inputs and direct outputs must be declared</b></span>"
(where this agrees with the definitions above) can we do the
following for the build rule of a haskell object file X.o?</p>
<ol>
<li>`need` the shallow dependencies as reported by `ghc -M`. This
guarantees that all shallow and deep dependencies (i.e. all
direct dependencies) are built.<br>
</li>
<li>build X.o and X.hi</li>
<li>Inspect X.hi to derive the direct dependencies (and hence deep
dependencies)</li>
<li>`needed` the deep dependencies</li>
</ol>
<p>Is there already an easy way to inspect *.hi files in this way?
Is this use of `needed` valid?</p>
<p>- David E<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 3/27/19 3:05 PM, Andrey Mokhov
wrote:<br>
</div>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Hi
David,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">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:<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoListParagraph"
style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="font-size:11.0pt;font-family:Symbol;color:#1F497D;mso-fareast-language:EN-US"><span
style="mso-list:Ignore">·<span style="font:7.0pt
"Times New Roman"">
</span></span></span><!--[endif]--><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Non-cloud
build systems: *<b>all direct inputs must be declared</b>*.
If you miss a direct input dependency then a build may
complete successfully but with an incorrect result.<o:p></o:p></span></p>
<p class="MsoListParagraph"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoListParagraph"
style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="font-size:11.0pt;font-family:Symbol;color:#1F497D;mso-fareast-language:EN-US"><span
style="mso-list:Ignore">·<span style="font:7.0pt
"Times New Roman"">
</span></span></span><!--[endif]--><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Cloud
build systems: *<b>all direct inputs and direct outputs must
be declared</b>*. If you miss a direct output then a build
may fail because the cloud will not be able to restore the
corresponding output.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoListParagraph"
style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="font-size:11.0pt;font-family:Symbol;color:#1F497D;mso-fareast-language:EN-US"><span
style="mso-list:Ignore">·<span style="font:7.0pt
"Times New Roman"">
</span></span></span><!--[endif]--><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Cloud
build systems with shallow (deferred) materialisation of
build artefacts: *<b>all transitive inputs and direct
outputs must be declared</b>*. 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.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Having
said that, if we really access a file during compilation,
then I think it is *<b>not</b>* a transitive dependency by
definition! Any file which is accessed during a build rule
is a direct dependency.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">>
GHC is reading *.hi files that are not reported as
dependencies by<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">>
`ghc -M -include-pkg-deps`. This is because they are not
direct, but transitive<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">>
dependencies!<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">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?<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Thank
you for all your work on Hadrian!<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Cheers,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Andrey<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"
moz-do-not-send="true"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></a></p>
<div>
<div style="border:none;border-top:solid #E1E1E1
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext"
lang="EN-US">From:</span></b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext"
lang="EN-US"> David Eichmann
[<a class="moz-txt-link-freetext" href="mailto:davide@well-typed.com">mailto:davide@well-typed.com</a>]
<br>
<b>Sent:</b> 27 March 2019 12:54<br>
<b>To:</b> Neil Mitchell <a class="moz-txt-link-rfc2396E" href="mailto:ndmitchell@gmail.com"><ndmitchell@gmail.com></a>;
Andrey Mokhov <a class="moz-txt-link-rfc2396E" href="mailto:andrey.mokhov@newcastle.ac.uk"><andrey.mokhov@newcastle.ac.uk></a>; GHC
developers <a class="moz-txt-link-rfc2396E" href="mailto:ghc-devs@haskell.org"><ghc-devs@haskell.org></a><br>
<b>Subject:</b> Hadrian Transitive Dependencies<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p>Hello Shake/Hadrian contributors and the like,<o:p></o:p></p>
<p>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 <a
href="https://gitlab.haskell.org/ghc/ghc/issues/16295"
moz-do-not-send="true">
#16295</a>. This is very desirable to improve CI build
times. It is my understanding that in order to get caching to
work:<o:p></o:p></p>
<p class="MsoNormal">1. All accessed files must declared with
`need` AND<br>
2. All created files must be declared with `produces` (or be
the target of the build rule)
<o:p></o:p></p>
<p>Is my understanding correct? Or is there a weaker condition
(perhaps only 2 is necessary)?<o:p></o:p></p>
<p>If I'm correct, this amounts to fixing all fsatrace lint
errors. See <a
href="https://gitlab.haskell.org/ghc/ghc/issues/16400#note_188901"
moz-do-not-send="true">
here</a> 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:<o:p></o:p></p>
<pre>_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : libraries/mtl/Control/Monad/RWS/Class.hs<o:p></o:p></pre>
<pre>_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<o:p></o:p></pre>
<pre>_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<o:p></o:p></pre>
<pre>_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<o:p></o:p></pre>
<pre>_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<o:p></o:p></pre>
<pre>_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<o:p></o:p></pre>
<pre>_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<o:p></o:p></pre>
<pre>_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<o:p></o:p></pre>
<pre>_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<o:p></o:p></pre>
<pre>_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<o:p></o:p></pre>
<pre>_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/libraries/mtl/build/Control/Monad/Writer/Class.hi<o:p></o:p></pre>
<pre>_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/libraries/mtl/build/Control/Monad/State/Class.hi<o:p></o:p></pre>
<pre>_build/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o : _build/stage1/libraries/mtl/build/Control/Monad/Reader/Class.hi<o:p></o:p></pre>
<p>And shake complains of the following missing deps:<o:p></o:p></p>
<pre>_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<o:p></o:p></pre>
<pre>Lint checking error - _build/HEAD_default/stage1/libraries/mtl/build/Control/Monad/RWS/Class.o - 22 values were used but not depended upon:<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage0/lib/settings<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage0/lib/platformConstants<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage0/lib/llvm-targets<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage0/lib/llvm-passes<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage0/lib/package.conf.d/package.cache<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/package.conf.d/package.cache<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/Float.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/Base.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/ghc-prim-0.5.3/GHC/Types.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/Maybe.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Writer/Lazy.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Writer/Strict.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/State/Lazy.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/State/Strict.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Reader.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/List.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/transformers-0.5.5.0/Control/Monad/Trans/Cont.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/ghc-prim-0.5.3/GHC/Tuple.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/IO/Exception.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/integer-gmp-1.0.2.0/GHC/Integer/Type.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/Data/Either.hi<o:p></o:p></pre>
<pre> Used: _build/HEAD_default/stage1/lib/x86_64-linux-ghc-8.9.20190325/base-4.13.0.0/GHC/Natural.hi<o:p></o:p></pre>
<p>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
<i>transitive</i> dependencies! How do we fix these lint
errors (again with the goal of using shakes shared cache
feature)? Some ideas:<o:p></o:p></p>
<p class="MsoNormal">* Wildly over approximate dependencies.
This may be easier to implement but cause unneeded
recompilation (when a false dependency changes). Either:<br>
* `need` all dependent packages' interface files
recursively as well as transitive dependencies reported by
`ghc -M -include-pkg-deps` within the current package. OR<br>
* 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.<br>
* Perhaps transitive dependencies are not important for shared
caching to work. Change shakes linting feature to allow
(untracked?) transitive dependencies to be accessed.
<o:p></o:p></p>
<p>Feed back would be greatly appreciated.<o:p></o:p></p>
<p>David Eichmann<o:p></o:p></p>
<p><o:p> </o:p></p>
<pre>-- <o:p></o:p></pre>
<pre>David Eichmann, Haskell Consultant<o:p></o:p></pre>
<pre>Well-Typed LLP, <a href="http://www.well-typed.com" moz-do-not-send="true">http://www.well-typed.com</a><o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>Registered in England & Wales, OC335890<o:p></o:p></pre>
<pre>118 Wymering Mansions, Wymering Road, London W9 2NF, England <o:p></o:p></pre>
</div>
</blockquote>
<pre class="moz-signature" cols="72">--
David Eichmann, Haskell Consultant
Well-Typed LLP, <a class="moz-txt-link-freetext" href="http://www.well-typed.com">http://www.well-typed.com</a>
Registered in England & Wales, OC335890
118 Wymering Mansions, Wymering Road, London W9 2NF, England </pre>
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