249 lines
11 KiB
Makefile
249 lines
11 KiB
Makefile
# $NetBSD: varmod-ifelse.mk,v 1.21 2023/02/18 18:23:58 rillig Exp $
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#
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# Tests for the ${cond:?then:else} variable modifier, which evaluates either
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# the then-expression or the else-expression, depending on the condition.
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#
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# The modifier was added on 1998-04-01.
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#
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# Until 2015-10-11, the modifier always evaluated both the "then" and the
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# "else" expressions.
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# TODO: Implementation
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# The variable name of the expression is expanded and then taken as the
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# condition. In the below example it becomes:
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#
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# variable expression == "literal"
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#
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# This confuses the parser, which expects an operator instead of the bare
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# word "expression". If the name were expanded lazily, everything would be
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# fine since the condition would be:
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#
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# ${:Uvariable expression} == "literal"
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#
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# Evaluating the variable name lazily would require additional code in
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# Var_Parse and ParseVarname, it would be more useful and predictable
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# though.
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.if ${${:Uvariable expression} == "literal":?bad:bad}
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. error
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.else
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. error
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.endif
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# In a variable assignment, undefined variables are not an error.
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# Because of the early expansion, the whole condition evaluates to
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# ' == ""' though, which cannot be parsed because the left-hand side looks
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# empty.
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COND:= ${${UNDEF} == "":?bad-assign:bad-assign}
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# In a condition, undefined variables generate a "Malformed conditional"
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# error. That error message is wrong though. In lint mode, the correct
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# "Undefined variable" error message is generated.
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# The difference to the ':=' variable assignment is the additional
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# "Malformed conditional" error message.
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.if ${${UNDEF} == "":?bad-cond:bad-cond}
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. error
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.else
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. error
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.endif
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# When the :? is parsed, it is greedy. The else branch spans all the
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# text, up until the closing character '}', even if the text looks like
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# another modifier.
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.if ${1:?then:else:Q} != "then"
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. error
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.endif
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.if ${0:?then:else:Q} != "else:Q"
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. error
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.endif
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# This line generates 2 error messages. The first comes from evaluating the
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# malformed conditional "1 == == 2", which is reported as "Bad conditional
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# expression" by ApplyModifier_IfElse. The variable expression containing that
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# conditional therefore returns a parse error from Var_Parse, and this parse
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# error propagates to CondEvalExpression, where the "Malformed conditional"
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# comes from.
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.if ${1 == == 2:?yes:no} != ""
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. error
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.else
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. error
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.endif
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# If the "Bad conditional expression" appears in a quoted string literal, the
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# error message "Malformed conditional" is not printed, leaving only the "Bad
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# conditional expression".
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#
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# XXX: The left-hand side is enclosed in quotes. This results in Var_Parse
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# being called without VARE_UNDEFERR. When ApplyModifier_IfElse
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# returns AMR_CLEANUP as result, Var_Parse returns varUndefined since the
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# value of the variable expression is still undefined. CondParser_String is
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# then supposed to do proper error handling, but since varUndefined is local
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# to var.c, it cannot distinguish this return value from an ordinary empty
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# string. The left-hand side of the comparison is therefore just an empty
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# string, which is obviously equal to the empty string on the right-hand side.
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#
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# XXX: The debug log for -dc shows a comparison between 1.0 and 0.0. The
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# condition should be detected as being malformed before any comparison is
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# done since there is no well-formed comparison in the condition at all.
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.MAKEFLAGS: -dc
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.if "${1 == == 2:?yes:no}" != ""
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. error
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.else
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. warning Oops, the parse error should have been propagated.
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.endif
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.MAKEFLAGS: -d0
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# As of 2020-12-10, the variable "name" is first expanded, and the result of
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# this expansion is then taken as the condition. To force the variable
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# expression in the condition to be evaluated at exactly the right point,
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# the '$' of the intended '${VAR}' escapes from the parser in form of the
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# expression ${:U\$}. Because of this escaping, the variable "name" and thus
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# the condition ends up as "${VAR} == value", just as intended.
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#
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# This hack does not work for variables from .for loops since these are
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# expanded at parse time to their corresponding ${:Uvalue} expressions.
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# Making the '$' of the '${VAR}' expression indirect hides this expression
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# from the parser of the .for loop body. See ForLoop_SubstVarLong.
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.MAKEFLAGS: -dc
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VAR= value
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.if ${ ${:U\$}{VAR} == value:?ok:bad} != "ok"
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. error
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.endif
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.MAKEFLAGS: -d0
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# On 2021-04-19, when building external/bsd/tmux with HAVE_LLVM=yes and
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# HAVE_GCC=no, the following conditional generated this error message:
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#
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# make: Bad conditional expression 'string == "literal" && no >= 10'
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# in 'string == "literal" && no >= 10?yes:no'
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#
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# Despite the error message (which was not clearly marked with "error:"),
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# the build continued, for historical reasons, see main_Exit.
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#
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# The tricky detail here is that the condition that looks so obvious in the
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# form written in the makefile becomes tricky when it is actually evaluated.
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# This is because the condition is written in the place of the variable name
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# of the expression, and in an expression, the variable name is always
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# expanded first, before even looking at the modifiers. This happens for the
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# modifier ':?' as well, so when CondEvalExpression gets to see the
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# expression, it already looks like this:
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#
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# string == "literal" && no >= 10
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#
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# When parsing such an expression, the parser used to be strict. It first
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# evaluated the left-hand side of the operator '&&' and then started parsing
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# the right-hand side 'no >= 10'. The word 'no' is obviously a string
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# literal, not enclosed in quotes, which is OK, even on the left-hand side of
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# the comparison operator, but only because this is a condition in the
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# modifier ':?'. In an ordinary directive '.if', this would be a parse error.
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# For strings, only the comparison operators '==' and '!=' are defined,
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# therefore parsing stopped at the '>', producing the 'Bad conditional
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# expression'.
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#
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# Ideally, the conditional expression would not be expanded before parsing
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# it. This would allow to write the conditions exactly as seen below. That
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# change has a high chance of breaking _some_ existing code and would need
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# to be thoroughly tested.
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#
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# Since cond.c 1.262 from 2021-04-20, make reports a more specific error
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# message in situations like these, pointing directly to the specific problem
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# instead of just saying that the whole condition is bad.
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STRING= string
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NUMBER= no # not really a number
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.info ${${STRING} == "literal" && ${NUMBER} >= 10:?yes:no}.
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.info ${${STRING} == "literal" || ${NUMBER} >= 10:?yes:no}.
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# The following situation occasionally occurs with MKINET6 or similar
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# variables.
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NUMBER= # empty, not really a number either
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.info ${${STRING} == "literal" && ${NUMBER} >= 10:?yes:no}.
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.info ${${STRING} == "literal" || ${NUMBER} >= 10:?yes:no}.
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# CondParser_LeafToken handles [0-9-+] specially, treating them as a number.
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PLUS= +
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ASTERISK= *
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EMPTY= # empty
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# "true" since "+" is not the empty string.
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.info ${${PLUS} :?true:false}
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# "false" since the variable named "*" is not defined.
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.info ${${ASTERISK} :?true:false}
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# syntax error since the condition is completely blank.
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.info ${${EMPTY} :?true:false}
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# Since the condition of the '?:' modifier is expanded before being parsed and
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# evaluated, it is common practice to enclose expressions in quotes, to avoid
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# producing syntactically invalid conditions such as ' == value'. This only
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# works if the expanded values neither contain quotes nor backslashes. For
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# strings containing quotes or backslashes, the '?:' modifier should not be
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# used.
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PRIMES= 2 3 5 7 11
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.if ${1 2 3 4 5:L:@n@$n:${ ("${PRIMES:M$n}" != "") :?prime:not_prime}@} != \
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"1:not_prime 2:prime 3:prime 4:not_prime 5:prime"
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. error
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.endif
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# When parsing the modifier ':?', there are 3 possible cases:
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#
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# 1. The whole expression is only parsed.
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# 2. The expression is parsed and the 'then' branch is evaluated.
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# 3. The expression is parsed and the 'else' branch is evaluated.
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#
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# In all of these cases, the expression must be parsed in the same way,
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# especially when one of the branches contains unbalanced '{}' braces.
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#
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# At 2020-01-01, the expressions from the 'then' and 'else' branches were
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# parsed differently, depending on whether the branch was taken or not. When
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# the branch was taken, the parser recognized that in the modifier ':S,}},,',
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# the '}}' were ordinary characters. When the branch was not taken, the
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# parser only counted balanced '{' and '}', ignoring any escaping or other
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# changes in the interpretation.
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#
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# In var.c 1.285 from 2020-07-20, the parsing of the expressions changed so
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# that in both cases the expression is parsed in the same way, taking the
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# unbalanced braces in the ':S' modifiers into account. This change was not
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# on purpose, the commit message mentioned 'has the same effect', which was a
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# wrong assumption.
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#
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# In var.c 1.323 from 2020-07-26, the unintended fix from var.c 1.285 was
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# reverted, still not knowing about the difference between regular parsing and
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# balanced-mode parsing.
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#
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# In var.c 1.1028 from 2022-08-08, there was another attempt at fixing this
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# inconsistency in parsing, but since that broke parsing of the modifier ':@',
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# it was reverted in var.c 1.1029 from 2022-08-23.
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#
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# In var.c 1.1047 from 2023-02-18, the inconsistency in parsing was finally
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# fixed. The modifier ':@' now parses the body in balanced mode, while
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# everywhere else the modifier parts have their subexpressions parsed in the
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# same way, no matter whether they are evaluated or not.
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#
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# The modifiers ':@' and ':?' are similar in that they conceptually contain
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# text to be evaluated later or conditionally, still they parse that text
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# differently. The crucial difference is that the body of the modifier ':@'
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# is always parsed using balanced mode. The modifier ':?', on the other hand,
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# must parse both of its branches in the same way, no matter whether they are
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# evaluated or not. Since balanced mode and standard mode are incompatible,
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# it's impossible to use balanced mode in the modifier ':?'.
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.MAKEFLAGS: -dc
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.if 0 && ${1:?${:Uthen0:S,}},,}:${:Uelse0:S,}},,}} != "not evaluated"
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# At 2020-01-07, the expression evaluated to 'then0,,}}', even though it was
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# irrelevant as the '0' had already been evaluated to 'false'.
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. error
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.endif
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.if 1 && ${0:?${:Uthen1:S,}},,}:${:Uelse1:S,}},,}} != "else1"
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. error
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.endif
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.if 2 && ${1:?${:Uthen2:S,}},,}:${:Uelse2:S,}},,}} != "then2"
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# At 2020-01-07, the whole expression evaluated to 'then2,,}}' instead of the
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# expected 'then2'. The 'then' branch of the ':?' modifier was parsed
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# normally, parsing and evaluating the ':S' modifier, thereby treating the
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# '}}' as ordinary characters and resulting in 'then2'. The 'else' branch was
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# parsed in balanced mode, ignoring that the inner '}}' were ordinary
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# characters. The '}}' were thus interpreted as the end of the 'else' branch
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# and the whole expression. This left the trailing ',,}}', which together
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# with the 'then2' formed the result 'then2,,}}'.
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. error
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.endif
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.MAKEFLAGS: -d0
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