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* doc/make.texi (Prerequisite Types): [SV 58056] Clarify ordering.

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Paul Smith 2022-10-02 09:30:20 -04:00
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@ -2075,26 +2075,25 @@ extra features (@pxref{Recipes, ,Writing Recipes in Rules}).
@cindex normal prerequisites @cindex normal prerequisites
@cindex prerequisites, order-only @cindex prerequisites, order-only
@cindex order-only prerequisites @cindex order-only prerequisites
There are actually two different types of prerequisites understood by There are two different types of prerequisites understood by GNU @code{make}:
GNU @code{make}: normal prerequisites such as described in the normal prerequisites, described in the previous section, and @dfn{order-only}
previous section, and @dfn{order-only} prerequisites. A normal prerequisites. A normal prerequisite makes two statements: first, it imposes
prerequisite makes two statements: first, it imposes an order in which an order in which recipes will be invoked: the recipes for all prerequisites
recipes will be invoked: the recipes for all prerequisites of a target of a target will be completed before the recipe for the target is started.
will be completed before the recipe for the target is run. Second, it Second, it imposes a dependency relationship: if any prerequisite is newer
imposes a dependency relationship: if any prerequisite is newer than than the target, then the target is considered out-of-date and must be
the target, then the target is considered out-of-date and must be
rebuilt. rebuilt.
Normally, this is exactly what you want: if a target's prerequisite is Normally, this is exactly what you want: if a target's prerequisite is
updated, then the target should also be updated. updated, then the target should also be updated.
Occasionally, however, you have a situation where you want to impose a Occasionally you may want to ensure that a prerequisite is built before a
specific ordering on the rules to be invoked @emph{without} forcing target, but @emph{without} forcing the target to be updated if the
the target to be updated if one of those rules is executed. In that prerequisite is updated. @dfn{Order-only} prerequisites are used to create
case, you want to define @dfn{order-only} prerequisites. Order-only this type of relationship. Order-only prerequisites can be specified by
prerequisites can be specified by placing a pipe symbol (@code{|}) placing a pipe symbol (@code{|}) in the prerequisites list: any prerequisites
in the prerequisites list: any prerequisites to the left of the pipe to the left of the pipe symbol are normal; any prerequisites to the right are
symbol are normal; any prerequisites to the right are order-only: order-only:
@example @example
@var{targets} : @var{normal-prerequisites} | @var{order-only-prerequisites} @var{targets} : @var{normal-prerequisites} | @var{order-only-prerequisites}