make(1): add tests and tutorial for the ?= assignment operator
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rillig
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@ -1,4 +1,4 @@
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# $NetBSD: mi,v 1.984 2020/12/07 07:51:25 rillig Exp $
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# $NetBSD: mi,v 1.985 2020/12/07 21:35:43 rillig Exp $
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#
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# Note: don't delete entries from here - mark them as "obsolete" instead.
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#
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@ -5263,8 +5263,8 @@
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./usr/tests/usr.bin/make/unit-tests/posix.mk tests-usr.bin-tests compattestfile,atf
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./usr/tests/usr.bin/make/unit-tests/posix1.exp tests-usr.bin-tests compattestfile,atf
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./usr/tests/usr.bin/make/unit-tests/posix1.mk tests-usr.bin-tests compattestfile,atf
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./usr/tests/usr.bin/make/unit-tests/qequals.exp tests-usr.bin-tests compattestfile,atf
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./usr/tests/usr.bin/make/unit-tests/qequals.mk tests-usr.bin-tests compattestfile,atf
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./usr/tests/usr.bin/make/unit-tests/qequals.exp tests-obsolete obsolete,atf
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./usr/tests/usr.bin/make/unit-tests/qequals.mk tests-obsolete obsolete,atf
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./usr/tests/usr.bin/make/unit-tests/recursive.exp tests-usr.bin-tests compattestfile,atf
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./usr/tests/usr.bin/make/unit-tests/recursive.mk tests-usr.bin-tests compattestfile,atf
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./usr/tests/usr.bin/make/unit-tests/sh-dots.exp tests-usr.bin-tests compattestfile,atf
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@ -1,4 +1,4 @@
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# $NetBSD: Makefile,v 1.238 2020/12/07 01:32:04 rillig Exp $
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# $NetBSD: Makefile,v 1.239 2020/12/07 21:35:43 rillig Exp $
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#
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# Unit tests for make(1)
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#
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@ -257,7 +257,6 @@ TESTS+= parse-var
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TESTS+= phony-end
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TESTS+= posix
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TESTS+= # posix1 # broken by reverting POSIX changes
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TESTS+= qequals
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TESTS+= recursive
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TESTS+= sh
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TESTS+= sh-dots
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@ -1,2 +0,0 @@
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V.i386 ?= OK
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exit status 0
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@ -1,8 +0,0 @@
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# $NetBSD: qequals.mk,v 1.3 2020/10/24 08:50:17 rillig Exp $
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M= i386
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V.i386= OK
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V.$M?= bug
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all:
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@echo 'V.$M ?= ${V.$M}'
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@ -1,9 +1,77 @@
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# $NetBSD: var-op-default.mk,v 1.2 2020/08/16 14:25:16 rillig Exp $
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# $NetBSD: var-op-default.mk,v 1.3 2020/12/07 21:35:43 rillig Exp $
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#
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# Tests for the ?= variable assignment operator, which only assigns
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# if the variable is still undefined.
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# TODO: Implementation
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# The variable VAR is not defined yet. Therefore it gets the default value
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# from the variable assignment.
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VAR?= default value
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.if ${VAR} != "default value"
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. error
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.endif
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# At this point, the variable 'VAR' is already defined. The '?=' therefore
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# ignores the new variable value, preserving the previous "default value".
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VAR?= ignored
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.if ${VAR} != "default value"
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. error
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.endif
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# The '?=' operator only checks whether the variable is defined or not.
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# An empty variable is defined, therefore the '?=' operator does nothing.
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EMPTY= # empty
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EMPTY?= ignored
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.if ${EMPTY} != ""
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. error
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.endif
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# The .for loop is described in the manual page as if it would operate on
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# variables. This is not entirely true. Instead, each occurrence of an
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# expression $i or ${i} or ${i:...} is substituted with ${:Uloop-value}.
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# This comes very close to the description, the only difference is that
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# there is never an actual variable named 'i' involved.
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#
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# Because there is not really a variable named 'i', the '?=' operator
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# performs the variable assignment, resulting in $i == "default".
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.for i in loop-value
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i?= default
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.endfor
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.if ${i} != "default"
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. error
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.endif
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# At the point where the '?=' operator checks whether the variable exists,
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# it expands the variable name exactly once. Therefore both 'VAR.param'
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# and 'VAR.${param}' expand to 'VAR.param', and the second '?=' assignment
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# has no effect.
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#
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# Since 2000.05.11.07.43.42 it has been possible to use nested variable
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# expressions in variable names, which made make much more versatile.
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# On 2008.03.31.00.12.21, this particular case of the '?=' operator has been
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# fixed. Before, the '?=' operator had not expanded the variable name
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# 'VAR.${:Uparam}' to see whether the variable already existed. Since that
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# variable didn't exist (and variables with '$' in their name are particularly
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# fragile), the variable assignment with "not used" was performed, and only
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# during that, the variable name was expanded.
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VAR.param= already defined
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VAR.${:Uparam}?= not used
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.if ${VAR.param} != "already defined"
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. error
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.endif
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# Now demonstrate that the variable name is indeed expanded exactly once.
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# This is tricky to measure correctly since there are many inconsistencies
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# in and around the code that expands variable expressions in the various
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# places where variable expressions can occur. If in doubt, enable the
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# following debug flags to see what happens:
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#.MAKEFLAGS: -dcpv
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EXPAND_NAME= EXPAND.$$$$ # The full variable name is EXPAND.$$
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PARAM= $$$$
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EXPAND.${PARAM}?= value with param
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.if ${${EXPAND_NAME}} != "value with param"
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. error
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.endif
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.MAKEFLAGS: -d0
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all:
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@:;
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