[Omake] Wildcards in functions used within dependencies

[Aleksey Nogin]

On 26.08.2007 06:39, John Billings wrote:

> Hello,
> 
> I'd like to specify a rule of the form:
> 
>   %.done: $(CProgram %, %)
>    ./$< && touch $@
> 
> The problem is that the `%' does not appear to be recognised as a
> wildcard within the CProgram function call; it's interpreted as the
> literal value `%', and hence compilation fails with:
> 
>    Do not know how to build "%.o" required for "%"

John,

Sorry for taking so long to respond. There are two issues here.

First, there is an issue of the evaluation order - the dependencies in 
the implicit ("pattern") rules are evaluated when the _implicit_ rule is 
created, not when the rule is instantiated. So in the code you use, the 
"$(CProgram %, %)" will be called as soon as the rule is encountered, so 
you get a rule for building the program "%" out of "%.o" and an implicit 
rule

%.done: "%"
   ...

where the second "%" is taken literally. So the error message you get is 
expected and "natural".

You can change the evaluation order by using the "section rule" construct:

%.done:
    section rule
       %.done: $(CProgram %, %)
          ./$< && touch $@

One you do that, unfortunately you'd hit the second issue - currently, 
OMake does not allow new rules to be created once the OMakefiles are 
read and the build phase starts (the only exceptions are instantiations 
of implicit rules). Because of that, in the code above the rules created 
by the CProgram function will be ignored and running "omake foo.done" 
will get you "Don not know how to build foo" error. Contrary to the 
first issue, I do not think that this is "natural" - it was simply an 
implementation choice not to allow new rules during the build phase and 
I do not thing there is any good reason for that semantics.

I've filed an RFE http://bugzilla.metaprl.org/show_bug.cgi?id=691 where 
I argue that creating arbitrary new rules in "section rule" should be 
allowed.

Aleksey

-- 
Aleksey Nogin, Research Scientist
Advanced Technologies Department, Information & System Sciences Lab
HRL Laboratories, LLC, Malibu, CA