Re: simple explanation for order-only prerequisite?

[Robert P. J. Day]

On Sun, 3 Nov 2019, Nicholas Clark wrote:

> I'd describe OOPs as "just like a regular dependency, except that
> the timestamp isn't checked. Only whether it exists on the
> filesystem."

  is it really that simple? just a test for "does it exist or not?"
that suggests that make would not even bother consulting the rule for
that OOP.

  i thought it was a bit more complicated in that make would still
check the rule for the OOP and, if there were any prerequisites that
had a newer timestamp, the OOP's recipe would be invoked, but beyond
that, that would have no dependency effect on the original target. in
short, an OOP would still be *processed* normally, it would just have
no further effect.

  i'm trying to think of an example so what about this one. imagine a
massive SW project, one of whose dependencies is "docs", to update the
documentation. now if any of the (say) markdown files is updated, then
the "docs" recipe is invoked to update the online docs. however, since
documentation has no effect on the actual software, there is no point
letting that target have any further effect in terms of recompiling
anything.

  might not be the best example, but is it accurate?

rday