Hadrian Transitive Dependencies

David Eichmann davide at well-typed.com
Thu Mar 28 15:21:27 UTC 2019

I've started a wiki page to document some of this discussion 
https://gitlab.haskell.org/ghc/ghc/wikis/Developing-Hadrian. We'll also 
need to deal with ouputs as well as inputs (dependencies) soon. Hence 
I've expanded a bit on my understanding of rule *outputs* and added the 
terms "vital input" and "vital output" (does it make sense? is there a 
better name here?). I've slightly changed the definition of "shallow 
dependencies" so that by definition it is a (minimal) subset of direct 
dependencies such that "/no change in the shallow dependencies -> no 
change in the vial output/" The important part to take away is that 
rules must:

  * `need` all shallow dependencies.
  * |`produces|` all vital outputs (excluding the rule target).

David E

On 3/27/19 11:23 PM, Andrey Mokhov wrote:
> Simon:
> > Perhaps the remaining un-tracked dependencies will be fewer and 
> easier to nail?
> There are a few other cases where we `need` only a subset of direct 
> dependencies that "cover" all others. For example, `setup-config` 
> files produced when configuring a package are used to signal the 
> completion of package configuration, which might produce a few other 
> hard-to-predict files, such as “build/include/HsBaseConfig.h”.
> I just realised that if one wants to have “hermetic builds”, where 
> build commands are executed in a sandbox, then it is absolutely 
> necessary to declare all direct dependencies without exception, 
> because they will need to be made available in the sandbox for the 
> build command to succeed.
> David:
> > Perhaps the best step forward is to simply silence the linting
> > using `trackAllow ["//*.hi"]` for haskell object rules. Then
> > I can continue tracking down other missing dependencies in
> > Hadrian with fsatrace linting.
> Yes, this looks like the best approach for now.
> Cheers,
> Andrey
David Eichmann, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com

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