bin/60850: Make could do with a syntax for immediate var expansion

["kre%munnari.OZ.AU@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60850
>Category:       bin
>Synopsis:       Make could do with a syntax for immediate var expansion
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Mon Oct 05 05:40:00 +0000 2026
>Originator:     Robert Elz
>Release:        NetBSD
>Organization:
>Environment:
Machine: everything
>Description:
	There are times when Make variables are transitory, existing
	just for a short period before vanishing.   They can be expanded
	while they exist, but not afterwards.   This means that a
	typical assignment like
		CFLAGS= -D${Var}
	doesn't work if Var is one of those transitory variables, as
	it will not have a value when CFLAGS is later expanded.

	This leads to nonsense like
		XVar:=${Var}
		CFLAGS= -D${XVar}
	which works OK, if Var only ever has one value, so only one
	"XVar" is needed to hold that value, it starts becoming
	freakish when Var goes through many different values, and
	all (or some subset) of them are needed.

	Better would be to simply have a syntax which instructs
	make to "expand this variable right now, whatever the context"
	which (assuming here it might be $[...] - but I don't care what
	the syntax is, $<var> wouldn't work as $< already has a meaning,
	but ${=Var} or something like that might work (no idea, I don't
	understand make).

	Then
		CFLAGS= -D$[Var]

	would simply assign something like

		CFLAGS= -DMake_Is_too_Complex

	which is generally what is wanted anyway, it is very rare
	to do an assignment like that, and expect the value of the
	variable to change later, and actually want to use the changed
	value.

>How-To-Repeat:
	Try makeing a Makefile.inc that has something like

		CPPFLAGS+= -I ${.PARSEDIR}

	in it, and see if you can make that work when CPPFLAGS
	ends up being used in one of the standard build rules
	from the bsd.*.mk files.

>Fix:
	Introduce sanity.