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cdde9e894d
Features of interest: Allow setting target local variables (similar to gmake) In META_MODE .MAKE.META.CMP_FILTER can be used for filtering commands before comparion. contrib/bmake/mk/cc-wrap.mk is an example of using these See ChangeLog for the gory details.
282 lines
8.6 KiB
Makefile
282 lines
8.6 KiB
Makefile
# $NetBSD: cond-short.mk,v 1.19 2021/12/27 18:54:19 rillig Exp $
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#
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# Demonstrates that in conditions, the right-hand side of an && or ||
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# is only evaluated if it can actually influence the result.
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# This is called 'short-circuit evaluation' and is the usual evaluation
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# mode in most programming languages. A notable exception is Ada, which
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# distinguishes between the operators 'And', 'And Then', 'Or', 'Or Else'.
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#
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# Before 2020-06-28, the right-hand side of an && or || operator was always
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# evaluated, which was wrong. In cond.c 1.69 and var.c 1.197 on 2015-10-11,
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# Var_Parse got a new parameter named 'wantit'. Since then it would have been
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# possible to skip evaluation of irrelevant variable expressions and only
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# parse them. They were still evaluated though, the only difference to
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# relevant variable expressions was that in the irrelevant variable
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# expressions, undefined variables were allowed. This allowed for conditions
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# like 'defined(VAR) && ${VAR:S,from,to,} != ""', which no longer produced an
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# error message 'Malformed conditional', but the irrelevant expression was
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# still evaluated.
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#
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# Since the initial commit on 1993-03-21, the manual page has been saying that
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# make 'will only evaluate a conditional as far as is necessary to determine',
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# but that was wrong. The code in cond.c 1.1 from 1993-03-21 looks good since
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# it calls Var_Parse(condExpr, VAR_CMD, doEval,&varSpecLen,&doFree), but the
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# definition of Var_Parse did not call the third parameter 'doEval', as would
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# be expected, but instead 'err', accompanied by the comment 'TRUE if
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# undefined variables are an error'. This subtle difference between 'do not
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# evaluate at all' and 'allow undefined variables' led to the unexpected
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# evaluation.
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#
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# See also:
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# var-eval-short.mk, for short-circuited variable modifiers
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# The && operator:
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.if 0 && ${echo "unexpected and" 1>&2 :L:sh}
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.endif
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.if 1 && ${echo "expected and" 1>&2 :L:sh}
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.endif
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.if 0 && exists(nonexistent${echo "unexpected and exists" 1>&2 :L:sh})
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.endif
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.if 1 && exists(nonexistent${echo "expected and exists" 1>&2 :L:sh})
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.endif
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.if 0 && empty(${echo "unexpected and empty" 1>&2 :L:sh})
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.endif
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.if 1 && empty(${echo "expected and empty" 1>&2 :L:sh})
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.endif
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# "VAR U11" is not evaluated; it was evaluated before 2020-07-02.
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# The whole !empty condition is only parsed and then discarded.
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VAR= ${VAR${:U11${echo "unexpected VAR U11" 1>&2 :L:sh}}}
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VAR13= ${VAR${:U12${echo "unexpected VAR13" 1>&2 :L:sh}}}
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.if 0 && !empty(VAR${:U13${echo "unexpected U13 condition" 1>&2 :L:sh}})
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.endif
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VAR= ${VAR${:U21${echo "unexpected VAR U21" 1>&2 :L:sh}}}
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VAR23= ${VAR${:U22${echo "expected VAR23" 1>&2 :L:sh}}}
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.if 1 && !empty(VAR${:U23${echo "expected U23 condition" 1>&2 :L:sh}})
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.endif
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VAR= # empty again, for the following tests
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# The :M modifier is only parsed, not evaluated.
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# Before 2020-07-02, it was wrongly evaluated.
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.if 0 && !empty(VAR:M${:U${echo "unexpected M pattern" 1>&2 :L:sh}})
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.endif
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.if 1 && !empty(VAR:M${:U${echo "expected M pattern" 1>&2 :L:sh}})
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.endif
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.if 0 && !empty(VAR:S,from,${:U${echo "unexpected S modifier" 1>&2 :L:sh}},)
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.endif
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.if 0 && !empty(VAR:C,from,${:U${echo "unexpected C modifier" 1>&2 :L:sh}},)
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.endif
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.if 0 && !empty("" == "" :? ${:U${echo "unexpected ? modifier" 1>&2 :L:sh}} :)
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.endif
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.if 0 && !empty(VAR:old=${:U${echo "unexpected = modifier" 1>&2 :L:sh}})
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.endif
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.if 0 && !empty(1 2 3:L:@var@${:U${echo "unexpected @ modifier" 1>&2 :L:sh}}@)
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.endif
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.if 0 && !empty(:U${:!echo "unexpected exclam modifier" 1>&2 !})
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.endif
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# Irrelevant assignment modifiers are skipped as well.
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.if 0 && ${1 2 3:L:@i@${FIRST::?=$i}@}
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.endif
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.if 0 && ${1 2 3:L:@i@${LAST::=$i}@}
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.endif
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.if 0 && ${1 2 3:L:@i@${APPENDED::+=$i}@}
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.endif
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.if 0 && ${echo.1 echo.2 echo.3:L:@i@${RAN::!=${i:C,.*,&; & 1>\&2,:S,., ,g}}@}
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.endif
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.if defined(FIRST) || defined(LAST) || defined(APPENDED) || defined(RAN)
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. warning first=${FIRST} last=${LAST} appended=${APPENDED} ran=${RAN}
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.endif
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# The || operator:
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.if 1 || ${echo "unexpected or" 1>&2 :L:sh}
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.endif
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.if 0 || ${echo "expected or" 1>&2 :L:sh}
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.endif
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.if 1 || exists(nonexistent${echo "unexpected or exists" 1>&2 :L:sh})
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.endif
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.if 0 || exists(nonexistent${echo "expected or exists" 1>&2 :L:sh})
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.endif
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.if 1 || empty(${echo "unexpected or empty" 1>&2 :L:sh})
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.endif
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.if 0 || empty(${echo "expected or empty" 1>&2 :L:sh})
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.endif
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# Unreachable nested conditions are skipped completely as well. These skipped
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# lines may even contain syntax errors. This allows to skip syntactically
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# incompatible new features in older versions of make.
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.if 0
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. if ${echo "unexpected nested and" 1>&2 :L:sh}
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. endif
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.endif
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.if 1
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.elif ${echo "unexpected nested or" 1>&2 :L:sh}
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.endif
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# make sure these do not cause complaint
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#.MAKEFLAGS: -dc
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# TODO: Rewrite this whole section and check all the conditions and variables.
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# Several of the assumptions are probably wrong here.
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# TODO: replace 'x=' with '.info' or '.error'.
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V42= 42
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iV1= ${V42}
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iV2= ${V66}
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.if defined(V42) && ${V42} > 0
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x= Ok
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.else
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x= Fail
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.endif
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x!= echo 'defined(V42) && $${V42} > 0: $x' >&2; echo
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# With cond.c 1.76 from 2020-07-03, the following condition triggered a
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# warning: "String comparison operator should be either == or !=".
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# This was because the variable expression ${iV2} was defined, but the
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# contained variable V66 was undefined. The left-hand side of the comparison
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# therefore evaluated to the string "${V66}", which is obviously not a number.
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#
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# This was fixed in cond.c 1.79 from 2020-07-09 by not evaluating irrelevant
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# comparisons. Instead, they are only parsed and then discarded.
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#
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# At that time, there was not enough debug logging to see the details in the
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# -dA log. To actually see it, add debug logging at the beginning and end of
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# Var_Parse.
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.if defined(V66) && ( ${iV2} < ${V42} )
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x= Fail
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.else
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x= Ok
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.endif
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# XXX: This condition doesn't match the one above. The quotes are missing
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# above. This is a crucial detail since without quotes, the variable
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# expression ${iV2} evaluates to "${V66}", and with quotes, it evaluates to ""
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# since undefined variables are allowed and expand to an empty string.
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x!= echo 'defined(V66) && ( "$${iV2}" < $${V42} ): $x' >&2; echo
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.if 1 || ${iV1} < ${V42}
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x= Ok
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.else
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x= Fail
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.endif
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x!= echo '1 || $${iV1} < $${V42}: $x' >&2; echo
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# With cond.c 1.76 from 2020-07-03, the following condition triggered a
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# warning: "String comparison operator should be either == or !=".
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# This was because the variable expression ${iV2} was defined, but the
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# contained variable V66 was undefined. The left-hand side of the comparison
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# therefore evaluated to the string "${V66}", which is obviously not a number.
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#
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# This was fixed in cond.c 1.79 from 2020-07-09 by not evaluating irrelevant
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# comparisons. Instead, they are only parsed and then discarded.
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#
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# At that time, there was not enough debug logging to see the details in the
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# -dA log. To actually see it, add debug logging at the beginning and end of
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# Var_Parse.
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.if 1 || ${iV2:U2} < ${V42}
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x= Ok
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.else
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x= Fail
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.endif
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x!= echo '1 || $${iV2:U2} < $${V42}: $x' >&2; echo
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# the same expressions are fine when the lhs is expanded
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# ${iV1} expands to 42
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.if 0 || ${iV1} <= ${V42}
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x= Ok
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.else
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x= Fail
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.endif
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x!= echo '0 || $${iV1} <= $${V42}: $x' >&2; echo
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# ${iV2:U2} expands to 2
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.if 0 || ${iV2:U2} < ${V42}
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x= Ok
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.else
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x= Fail
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.endif
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x!= echo '0 || $${iV2:U2} < $${V42}: $x' >&2; echo
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# The right-hand side of the '&&' is irrelevant since the left-hand side
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# already evaluates to false. Before cond.c 1.79 from 2020-07-09, it was
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# expanded nevertheless, although with a small modification: undefined
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# variables may be used in these expressions without generating an error.
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.if defined(UNDEF) && ${UNDEF} != "undefined"
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. error
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.endif
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# Ensure that irrelevant conditions do not influence the result of the whole
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# condition. As of cond.c 1.302 from 2021-12-11, an irrelevant function call
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# evaluates to true (see CondParser_FuncCall and CondParser_FuncCallEmpty), an
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# irrelevant comparison evaluates to false (see CondParser_Comparison).
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#
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# An irrelevant true bubbles up to the outermost CondParser_And, where it is
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# ignored. An irrelevant false bubbles up to the outermost CondParser_Or,
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# where it is ignored.
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#
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# If the condition parser should ever be restructured, the bubbling up of the
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# irrelevant evaluation results might show up accidentally. Prevent this.
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DEF= defined
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.undef UNDEF
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.if 0 && defined(DEF)
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. error
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.endif
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.if 1 && defined(DEF)
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.else
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. error
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.endif
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.if 0 && defined(UNDEF)
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. error
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.endif
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.if 1 && defined(UNDEF)
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. error
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.endif
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.if 0 || defined(DEF)
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.else
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. error
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.endif
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.if 1 || defined(DEF)
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.else
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. error
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.endif
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.if 0 || defined(UNDEF)
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. error
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.endif
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.if 1 || defined(UNDEF)
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.else
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. error
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.endif
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all:
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