dba7b0ef92
Changes of interest
o unit-tests: use private TMPDIR to avoid errors from other users
o avoid strdup in mkTempFile
o always use vfork
o job.c: do not create empty shell files in jobs mode
reduce unnecessary calls to waitpid
o cond.c: fix debug output for comparison operators in conditionals
70 lines
2.6 KiB
Makefile
Executable File
70 lines
2.6 KiB
Makefile
Executable File
# $NetBSD: varname-empty.mk,v 1.8 2021/02/03 08:34:15 rillig Exp $
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#
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# Tests for the special variable with the empty name.
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#
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# There is no variable named "" at all, and this fact is used a lot in
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# variable expressions of the form ${:Ufallback}. These expressions are
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# based on the variable named "" and use the :U modifier to assign a
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# fallback value to the expression (but not to the variable).
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#
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# This form of expressions is used to implement value substitution in the
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# .for loops. Another use case is in a variable assignment of the form
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# ${:Uvarname}=value, which allows for characters in the variable name that
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# would otherwise be interpreted by the parser, such as whitespace, ':',
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# '=', '$', backslash.
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#
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# The only places where a variable is assigned a value are Var_Set and
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# Var_Append, and these places protect the variable named "" from being
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# defined. This is different from read-only variables, as that flag can
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# only apply to variables that are defined. The variable named "" must
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# never be defined though.
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#
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# See also:
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# The special variables @F or ^D, in var-class-local.mk
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# Until 2020-08-22 it was possible to assign a value to the variable with
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# the empty name, leading to all kinds of unexpected effects in .for loops
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# and other places that assume that ${:Ufallback} expands to "fallback".
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# The bug in Var_Set was that only expanded variables had been checked for
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# the empty name, but not the direct assignments with an empty name.
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?= default
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= assigned # undefined behavior until 2020-08-22
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+= appended
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:= subst
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!= echo 'shell-output'
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.if ${:Ufallback} != "fallback"
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. error
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.endif
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${:U}= assigned indirectly
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.if ${:Ufallback} != "fallback"
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. error
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.endif
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${:U}+= appended indirectly
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.if ${:Ufallback} != "fallback"
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. error
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.endif
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.MAKEFLAGS: -d0
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# Before 2020-08-22, the simple assignment operator '=' after an empty
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# variable name had an off-by-one bug in Parse_DoVar. The code that was
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# supposed to "skip to operator character" started its search _after_ the
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# assignment operator, assuming that the variable name would be at least
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# one character long. It then looked for the next occurrence of a '=', which
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# could be several lines away or not occur at all. While looking for the
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# '=', some whitespace was nulled out, leading to out-of-bounds write.
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= assigned # undefined behavior until 2020-08-22
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# The .for loop expands the expression ${i} to ${:U1}, ${:U2} and so on.
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# This only works if the variable with the empty name is guaranteed to
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# be undefined.
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.for i in 1 2 3
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NUMBERS+= ${i}
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.endfor
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all:
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@echo out: ${:Ufallback}
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@echo out: ${NUMBERS}
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