[Omake] Subtle dependency problem

[Aleksey Nogin]

Alain,

Would not it work correctly if you simply copy the dependencies 
recursively? In other words, if you are copying foo.cmi and you have 
foo.cmi: bar.cmi dependency, then you also copy bar.cmi? Or would this 
result in copying way too much?

Aleksey

On 29.05.2008 09:50, Alain Frisch wrote:

> Dear omake community,
> 
> (Nicolas is in Cc: in case the discussion also concerns ocamlbuild.)
> 
> In OCaml, some dependencies can only be discovered at type-checking 
> time. Indeed, consider the following modules:
> 
> a.ml:
> type t = int
> 
> b.ml:
> let x : A.t = 1
> 
> c.ml:
> B.x + 1
> 
> To compile c.ml, we need not only to read b.cmi, but also a.cmi. 
> Unfortunately, there is no way to know that by simply looking at its 
> code. So of course, ocamldep misses this dependency:
> 
> $ ocamldep -modules c.ml
> c.ml: B
> 
> In general, this is not a problem, because the build system will compile 
> b.ml before c.ml, and so a.cmi will be available anyway. But consider 
> the following scenario: c.ml is in another directory than a.ml and b.ml 
> and instead of adding an extra -I option, we want to copy a.cmi and 
> b.cmi into its directory. So we add to the OMakefile some copying rules 
> (with proper dependencies) for these two files. But now, nothing forces 
> omake to copy a.cmi in c.ml's directory before compiling c.ml.
> 
> This produces tricky errors that are difficult to diagnose because often 
> the file a.cmi has already been copied by a former compilation.
> 
> A simple way to simplify the diagnosis would be to parse the .cmi files
> after the compilation in order to check that all real dependencies had 
> been found by omake. I know how to handle the 'parsing the .cmi' part, 
> but I don't know how to implement the 'check' part. Any idea?
> 
> 
> How should the problem be really addressed? Of course, it is possible to 
> force an explicit dependency from c.ml to a.ml (by adding a dummy open 
> statement for instance), but this is not very satisfactory. We could 
> argue that copying .cmi files around is a bad idea, but there are good 
> reasons to do so.
> 
> Have people been confronted to such problems already?
> 
> 
> Alain
> 
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