Re: [Vala] Rules for updating generated C files

[Arc Riley <arcriley gmail com>]

Please do.  "This bug affects me too."

On Thu, Jun 3, 2010 at 5:13 PM, Robert Powell <rob yorba org> wrote:

> Hello,
>
> My understanding of the current rule for generating a C file from a vala
> file is, if the contents of the C file has the same hash value, don't
> rewrite the file.  When dealing with larger systems using libraries, this
> rule may not be sufficient.
>
> I've attached an example program that illustrates the problem I describe
> below.  To exhibit the problem:
> 1. execute make
> 2. execute ./main.  Note the output.
> 3. comment out the variable comment_and_uncomment_me in file
> BaseClass.vala.  Remember to save.
> 4. execute make
> 5. execute ./main.  Note the output is different and wrong.
>
> What is going on here
> -------------------------------
> We have a library BaseClass.vapi that is generated from BaseClass.vala.
> This defines the class BaseClass.  We also have Derived.vala, which defines
> a class that derives from BaseClass.
>
> If a member variable is added to BaseClass, BaseClass.vapi will change.
>  The
> C file that is generated from Derived.vala will be identical, but it needs
> to be recompiled because the base class has changed.  valac will not
> regenerate Derived.c because it hasn't changed.
>
> I propose that if the C file (Derived.c in this instance) that is generated
> has the same hash value as the existing C file BUT the corresponding vala
> file (Derived.vala) imports anything from a vapi (BaseClass.vapi) that has
> an earlier timestamp, the C file (Derived.c) should be touched.  Does valac
> have enough of this information to perform this check?
>
> For this simple system, it would be easy enough to update the makefile to
> watch for this dependency.  For larger systems, however, I could see that
> this could quickly get much more complex and error-prone.  I think that
> with
> the addition of this rule, it avoids this dependency problem.
>
> Is this a reasonable request?  Shall I file a bug?
>
> Thanks
>
> Rob
>
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