* Is there any way I can force simple expansion in recipes? If you really want to, you can generate the rule as part of the expansion of a variable, while arranging matters such that the recipe contains the expanded value. It's a powerful technique that lets you apply programmatic transformations to every rule, but then you're really writing in a different language, one that effectively compiles to GNU Make, with only the debugging tools for the lower level language.
________________________________ From: [email protected] on behalf of Alejandro Colomar Sent: Wednesday, September 10, 2025 14:38 To: Paul Smith Cc: [email protected] Subject: Re: [BUG] undefined variable used in recipe before undefine directive Hi Paul, On Wed, Sep 10, 2025 at 05:08:09PM -0400, Paul Smith wrote: > On Wed, 2025-09-10 at 22:33 +0200, Alejandro Colomar wrote: > > alx@debian:~/tmp/bug$ cat Makefile | nl -ba > > 1 MAKEFLAGS += --warn-undefined-variables > > 2 > > 3 foo := foo > > 4 > > 5 all:; echo $(foo) > > 6 > > 7 undefine foo > > alx@debian:~/tmp/bug$ make > > Makefile:5: warning: undefined variable 'foo' > > echo > > > > As I understand it, the variable foo is expanded immediately in the > > definition of the recipe > > No, you have it exactly backwards. Variables in recipes are deferred > and not expanded until the recipe is run. Hmmm, I see. Thanks! Is there any way I can force simple expansion in recipes? The reason I want to be able to undefine the variable name is to not need to come up with unique names in variables used within a recipe. That's why I immediately undefine it; to be able to reuse the name, making sure that old values are not used accidentally. And it may also improve performance. Maybe we could have something like '.IMMEDIATRECIPEEXPANSION:'. > > See: > https://www.gnu.org/software/make/manual/html_node/Reading-Makefiles.html > > > Rule Definition > > A rule is always expanded the same way, regardless of the form: > > > > immediate : immediate ; deferred > > deferred > > > > That is, the target and prerequisite sections are expanded > > immediately, and the recipe used to build the target is always > > deferred. This is true for explicit rules, pattern rules, suffix > > rules, static pattern rules, and simple prerequisite definitions. Thanks! Have a lovely night! Alex -- <https://www.alejandro-colomar.es> Use port 80 (that is, <...:80/>).
