06b9b3e0ad
Quite a lot of churn on style, but lots of
good work refactoring complicated functions
and lots more unit-tests.
Thanks mostly to rillig at NetBSD
Some interesting entries from ChangeLog
o .MAKE.{UID,GID} represent uid and gid running make.
o allow env var MAKE_OBJDIR_CHECK_WRITABLE=no to skip writable
checks in InitObjdir. Explicit .OBJDIR target always allows
read-only directory.
o add more unit tests for META MODE
Merge commit '8e11a9b4250be3c3379c45fa820bff78d99d5946' into main
Change-Id: I464fd4c013067f0915671c1ccc96d2d8090b2b9c
78 lines
2.8 KiB
Makefile
78 lines
2.8 KiB
Makefile
# $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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# 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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