1# $NetBSD: varmod-loop.mk,v 1.24 2023/11/19 21:47:52 rillig Exp $ 2# 3# Tests for the expression modifier ':@var@body@', which replaces each word of 4# the expression with the expanded body, which may contain references to the 5# variable 'var'. For example, '${1 2 3:L:@word@<${word}>@}' encloses each 6# word in angle quotes, resulting in '<1> <2> <3>'. 7# 8# The variable name can be chosen freely, except that it must not contain a 9# '$'. For simplicity and readability, variable names should only use the 10# characters 'A-Za-z0-9'. 11# 12# The body may contain subexpressions in the form '${...}' or '$(...)'. These 13# subexpressions differ from everywhere else in makefiles in that the parser 14# only scans '${...}' for balanced '{' and '}', likewise for '$(...)'. Any 15# other '$' is left as-is during parsing. Later, when the body is expanded 16# for each word, each '$$' is interpreted as a single '$', and the remaining 17# '$' are interpreted as expressions, like when evaluating a regular variable. 18 19# Force the test results to be independent of the default value of this 20# setting, which is 'yes' for NetBSD's usr.bin/make but 'no' for the bmake 21# distribution and pkgsrc/devel/bmake. 22.MAKE.SAVE_DOLLARS= yes 23 24all: varname-overwriting-target 25all: mod-loop-dollar 26 27varname-overwriting-target: 28 # Even "@" works as a variable name since the variable is installed 29 # in the "current" scope, which in this case is the one from the 30 # target. Because of this, after the loop has finished, '$@' is 31 # undefined. This is something that make doesn't expect, this may 32 # even trigger an assertion failure somewhere. 33 @echo :$@: :${:U1 2 3:@\@@x${@}y@}: :$@: 34 35 36# Demonstrate that it is possible to generate dollar signs using the 37# :@ modifier. 38# 39# These are edge cases that could have resulted in a parse error as well 40# since the $@ at the end could have been interpreted as a variable, which 41# would mean a missing closing @ delimiter. 42mod-loop-dollar: 43 @echo $@:${:U1:@word@${word}$@:Q}: 44 @echo $@:${:U2:@word@$${word}$$@:Q}: 45 @echo $@:${:U3:@word@$$${word}$$$@:Q}: 46 @echo $@:${:U4:@word@$$$${word}$$$$@:Q}: 47 @echo $@:${:U5:@word@$$$$${word}$$$$$@:Q}: 48 @echo $@:${:U6:@word@$$$$$${word}$$$$$$@:Q}: 49 50# It may happen that there are nested :@ modifiers that use the same name for 51# for the loop variable. These modifiers influence each other. 52# 53# As of 2020-10-18, the :@ modifier is implemented by actually setting a 54# variable in the scope of the expression and deleting it again after the 55# loop. This is different from the .for loops, which substitute the 56# expression with ${:Uvalue}, leading to different unwanted side effects. 57# 58# To make the behavior more predictable, the :@ modifier should restore the 59# loop variable to the value it had before the loop. This would result in 60# the string "1a b c1 2a b c2 3a b c3", making the two loops independent. 61.if ${:U1 2 3:@i@$i${:Ua b c:@i@$i@}${i:Uu}@} != "1a b cu 2a b cu 3a b cu" 62. error 63.endif 64 65# During the loop, the variable is actually defined and nonempty. 66# If the loop were implemented in the same way as the .for loop, the variable 67# would be neither defined nor nonempty since all expressions of the form 68# ${var} would have been replaced with ${:Uword} before evaluating them. 69.if defined(var) 70. error 71.endif 72.if ${:Uword:@var@${defined(var):?def:undef} ${empty(var):?empty:nonempty}@} \ 73 != "def nonempty" 74. error 75.endif 76.if defined(var) 77. error 78.endif 79 80# Assignment using the ':=' operator, combined with the :@var@ modifier 81# 828_DOLLARS= $$$$$$$$ 83# This string literal is written with 8 dollars, and this is saved as the 84# variable value. But as soon as this value is evaluated, it goes through 85# Var_Subst, which replaces each '$$' with a single '$'. This could be 86# prevented by VARE_EVAL_KEEP_DOLLAR, but that flag is usually removed 87# before expanding subexpressions. See ApplyModifier_Loop and 88# ParseModifierPart for examples. 89# 90.MAKEFLAGS: -dcp 91USE_8_DOLLARS= ${:U1:@var@${8_DOLLARS}@} ${8_DOLLARS} $$$$$$$$ 92.if ${USE_8_DOLLARS} != "\$\$\$\$ \$\$\$\$ \$\$\$\$" 93. error 94.endif 95# 96SUBST_CONTAINING_LOOP:= ${USE_8_DOLLARS} 97# The ':=' assignment operator evaluates the variable value using the mode 98# VARE_KEEP_DOLLAR_UNDEF, which means that some dollar signs are preserved, 99# but not all. The dollar signs in the top-level expression and in the 100# indirect ${8_DOLLARS} are preserved. 101# 102# The variable modifier :@var@ does not preserve the dollar signs though, no 103# matter in which context it is evaluated. What happens in detail is: 104# First, the modifier part "${8_DOLLARS}" is parsed without expanding it. 105# Next, each word of the value is expanded on its own, and at this moment 106# in ApplyModifier_Loop, the flag keepDollar is not passed down to 107# ModifyWords, resulting in "$$$$" for the first word of USE_8_DOLLARS. 108# 109# The remaining words of USE_8_DOLLARS are not affected by any variable 110# modifier and are thus expanded with the flag keepDollar in action. 111# The variable SUBST_CONTAINING_LOOP therefore gets assigned the raw value 112# "$$$$ $$$$$$$$ $$$$$$$$". 113# 114# The expression in the condition then expands this raw stored value 115# once, resulting in "$$ $$$$ $$$$". The effects from VARE_KEEP_DOLLAR no 116# longer take place since they had only been active during the evaluation of 117# the variable assignment. 118.if ${SUBST_CONTAINING_LOOP} != "\$\$ \$\$\$\$ \$\$\$\$" 119. error 120.endif 121.MAKEFLAGS: -d0 122 123# After looping over the words of the expression, the loop variable gets 124# undefined. The modifier ':@' uses an ordinary global variable for this, 125# which is different from the '.for' loop, which replaces ${var} with 126# ${:Uvalue} in the body of the loop. This choice of implementation detail 127# can be used for a nasty side effect. The expression ${:U:@VAR@@} evaluates 128# to an empty string, plus it undefines the variable 'VAR'. This is the only 129# possibility to undefine a global variable during evaluation. 130GLOBAL= before-global 131RESULT:= ${:U${GLOBAL} ${:U:@GLOBAL@@} ${GLOBAL:Uundefined}} 132.if ${RESULT} != "before-global undefined" 133. error 134.endif 135 136# The above side effect of undefining a variable from a certain scope can be 137# further combined with the otherwise undocumented implementation detail that 138# the argument of an '.if' directive is evaluated in cmdline scope. Putting 139# these together makes it possible to undefine variables from the cmdline 140# scope, something that is not possible in a straight-forward way. 141.MAKEFLAGS: CMDLINE=cmdline 142.if ${:U${CMDLINE}${:U:@CMDLINE@@}} != "cmdline" 143. error 144.endif 145# Now the cmdline variable got undefined. 146.if ${CMDLINE} != "cmdline" 147. error 148.endif 149# At this point, it still looks as if the cmdline variable were defined, 150# since the value of CMDLINE is still "cmdline". That impression is only 151# superficial though, the cmdline variable is actually deleted. To 152# demonstrate this, it is now possible to override its value using a global 153# variable, something that was not possible before: 154CMDLINE= global 155.if ${CMDLINE} != "global" 156. error 157.endif 158# Now undefine that global variable again, to get back to the original value. 159.undef CMDLINE 160.if ${CMDLINE} != "cmdline" 161. error 162.endif 163# What actually happened is that when CMDLINE was set by the '.MAKEFLAGS' 164# target in the cmdline scope, that same variable was exported to the 165# environment, see Var_SetWithFlags. 166.unexport CMDLINE 167.if ${CMDLINE} != "cmdline" 168. error 169.endif 170# The above '.unexport' has no effect since UnexportVar requires a global 171# variable of the same name to be defined, otherwise nothing is unexported. 172CMDLINE= global 173.unexport CMDLINE 174.undef CMDLINE 175.if ${CMDLINE} != "cmdline" 176. error 177.endif 178# This still didn't work since there must not only be a global variable, the 179# variable must be marked as exported as well, which it wasn't before. 180CMDLINE= global 181.export CMDLINE 182.unexport CMDLINE 183.undef CMDLINE 184.if ${CMDLINE:Uundefined} != "undefined" 185. error 186.endif 187# Finally the variable 'CMDLINE' from the cmdline scope is gone, and all its 188# traces from the environment are gone as well. To do that, a global variable 189# had to be defined and exported, something that is far from obvious. To 190# recap, here is the essence of the above story: 191.MAKEFLAGS: CMDLINE=cmdline # have a cmdline + environment variable 192.if ${:U:@CMDLINE@@}} # undefine cmdline, keep environment 193.endif 194CMDLINE= global # needed for deleting the environment 195.export CMDLINE # needed for deleting the environment 196.unexport CMDLINE # delete the environment 197.undef CMDLINE # delete the global helper variable 198.if ${CMDLINE:Uundefined} != "undefined" 199. error # 'CMDLINE' is gone now from all scopes 200.endif 201 202 203# In the loop body text of the ':@' modifier, a literal '$' is written as '$$', 204# not '\$'. In the following example, each '$$' turns into a single '$', 205# except for '$i', which is replaced with the then-current value '1' of the 206# iteration variable. 207# 208# See parse-var.mk, keyword 'BRACE_GROUP'. 209all: varmod-loop-literal-dollar 210varmod-loop-literal-dollar: .PHONY 211 : ${:U1:@i@ t=$$(( $${t:-0} + $i ))@} 212 213 214# When parsing the loop body, each '\$', '\@' and '\\' is unescaped to '$', 215# '@' and '\', respectively; all other backslashes are retained. 216# 217# In practice, the '$' is not escaped as '\$', as there is a second round of 218# unescaping '$$' to '$' later when the loop body is expanded after setting the 219# iteration variable. 220# 221# After the iteration variable has been set, the loop body is expanded with 222# this unescaping, regardless of whether .MAKE.SAVE_DOLLARS is set or not: 223# $$ a literal '$' 224# $x, ${var}, $(var) a nested expression 225# any other character itself 226all: escape-modifier 227escape-modifier: .PHONY 228 # In the first round, '\$ ' is unescaped to '$ ', and since the 229 # variable named ' ' is not defined, the expression '$ ' expands to an 230 # empty string. 231 # expect: : dollar=end 232 : ${:U1:@i@ dollar=\$ end@} 233 234 # Like in other modifiers, '\ ' is preserved, since ' ' is not one of 235 # the characters that _must_ be escaped. 236 # expect: : backslash=\ end 237 : ${:U1:@i@ backslash=\ end@} 238 239 # expect: : dollar=$ at=@ backslash=\ end 240 : ${:U1:@i@ dollar=\$\$ at=\@ backslash=\\ end@} 241 # expect: : dollar=$$ at=@@ backslash=\\ end 242 : ${:U1:@i@ dollar=\$\$\$\$ at=\@\@ backslash=\\\\ end@} 243 # expect: : dollar=$$ at=@@ backslash=\\ end 244 : ${:U1:@i@ dollar=$$$$ at=\@\@ backslash=\\\\ end@} 245 246all: .PHONY 247