Re: [Caml-list] "Inconsistent assumptions" when moving files across subdirectories

[Boris Yakobowski <boris@yakobowski.org>]

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Hi,

I can confirm you're not alone, unfortunately. In Frama-C (which uses good
ol' make), we have added a new target, dubbed 'smartclean', that removes
all orphaned .cm*. More precisely, if there exists a .cm* without a
corresponding .ml*, the .cm* is removed.

This is quite hackish, and not entirely satisfactory. Still, it's always
better than performing a full clean/rebuild.

HTH,

On Mon, Jun 1, 2015 at 11:52 PM, Josh Watzman <jwatzman@fb.com> wrote:

> I've noticed that it's pretty easy to confuse ocamlc/ocamlopt when moving
> a module across subdirectories. Here's an example, the most minimized repro
> I could get; it uses ocamlbuild, but a similar problem happens if you use
> OCamlMakefile and I assume other build systems.
> https://gist.github.com/jwatzman/9979951afb5b87304c18 -- running that
> will consistently terminate with the dreaded
>
> > Error: Files main.cmx and a/quux.cmx
> >        make inconsistent assumptions over interface Quux
>
> (The script flips the quux module back and forth twice, but that's only to
> exhibit the problem on both 4.01 and 4.02; you can get the same problem
> with only one move of quux.ml, but which way you need to move it depends
> on which version of ocaml you're using.)
>
> A clean build will of course resolve the problem, but that's quite
> annoying to have to go broadcast to a large team, particularly when the
> build may take many minutes, and when this problem is specific to the OCaml
> parts of our system (a humongous C++ codebase never requires a clean
> rebuild). Renaming a module across subdirectories doesn't seem like that
> uncommon of an operation.
>
> The root problem seems to be that ocamlc/ocamlopt are picking up build
> artifacts by directory only, and can't be explicitly told which artifacts
> to pick up, and so they are picking up the "wrong" quux.cmi/cmx left over
> in a build directory, which ocamlbuild should be cleaning up. Is that
> right? Is there any way to tell ocamlc/ocamlopt not to do things by
> directory, but to be more explicit, for the usages of build systems?
>
> Not working around this limitation of ocamlc/ocamlopt seems like a bug in
> ocamlbuild, no? I'm a bit surprised by it though, given that I've found the
> same problem in other build systems -- have other folks not run into this?
> How do other teams deal with this, trying to avoid clean builds?
>
> Thanks!
> Josh Watzman
>
>
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-- 
Boris

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