cond-short.mk revision 1.16
1 # $NetBSD: cond-short.mk,v 1.16 2021/03/14 11:49:37 rillig Exp $ 2 # 3 # Demonstrates that in conditions, the right-hand side of an && or || 4 # is only evaluated if it can actually influence the result. 5 # This is called 'short-circuit evaluation' and is the usual evaluation 6 # mode in most programming languages. A notable exception is Ada, which 7 # distinguishes between the operators 'And', 'And Then', 'Or', 'Or Else'. 8 # 9 # Before 2020-06-28, the right-hand side of an && or || operator was always 10 # evaluated, which was wrong. In cond.c 1.69 and var.c 1.197 on 2015-10-11, 11 # Var_Parse got a new parameter named 'wantit'. Since then it would have been 12 # possible to skip evaluation of irrelevant variable expressions and only 13 # parse them. They were still evaluated though, the only difference to 14 # relevant variable expressions was that in the irrelevant variable 15 # expressions, undefined variables were allowed. 16 # 17 # See also: 18 # var-eval-short.mk, for short-circuited variable modifiers 19 20 # The && operator: 21 22 .if 0 && ${echo "unexpected and" 1>&2 :L:sh} 23 .endif 24 25 .if 1 && ${echo "expected and" 1>&2 :L:sh} 26 .endif 27 28 .if 0 && exists(nonexistent${echo "unexpected and exists" 1>&2 :L:sh}) 29 .endif 30 31 .if 1 && exists(nonexistent${echo "expected and exists" 1>&2 :L:sh}) 32 .endif 33 34 .if 0 && empty(${echo "unexpected and empty" 1>&2 :L:sh}) 35 .endif 36 37 .if 1 && empty(${echo "expected and empty" 1>&2 :L:sh}) 38 .endif 39 40 # "VAR U11" is not evaluated; it was evaluated before 2020-07-02. 41 # The whole !empty condition is only parsed and then discarded. 42 VAR= ${VAR${:U11${echo "unexpected VAR U11" 1>&2 :L:sh}}} 43 VAR13= ${VAR${:U12${echo "unexpected VAR13" 1>&2 :L:sh}}} 44 .if 0 && !empty(VAR${:U13${echo "unexpected U13 condition" 1>&2 :L:sh}}) 45 .endif 46 47 VAR= ${VAR${:U21${echo "unexpected VAR U21" 1>&2 :L:sh}}} 48 VAR23= ${VAR${:U22${echo "expected VAR23" 1>&2 :L:sh}}} 49 .if 1 && !empty(VAR${:U23${echo "expected U23 condition" 1>&2 :L:sh}}) 50 .endif 51 VAR= # empty again, for the following tests 52 53 # The :M modifier is only parsed, not evaluated. 54 # Before 2020-07-02, it was wrongly evaluated. 55 .if 0 && !empty(VAR:M${:U${echo "unexpected M pattern" 1>&2 :L:sh}}) 56 .endif 57 58 .if 1 && !empty(VAR:M${:U${echo "expected M pattern" 1>&2 :L:sh}}) 59 .endif 60 61 .if 0 && !empty(VAR:S,from,${:U${echo "unexpected S modifier" 1>&2 :L:sh}},) 62 .endif 63 64 .if 0 && !empty(VAR:C,from,${:U${echo "unexpected C modifier" 1>&2 :L:sh}},) 65 .endif 66 67 .if 0 && !empty("" == "" :? ${:U${echo "unexpected ? modifier" 1>&2 :L:sh}} :) 68 .endif 69 70 .if 0 && !empty(VAR:old=${:U${echo "unexpected = modifier" 1>&2 :L:sh}}) 71 .endif 72 73 .if 0 && !empty(1 2 3:L:@var@${:U${echo "unexpected @ modifier" 1>&2 :L:sh}}@) 74 .endif 75 76 .if 0 && !empty(:U${:!echo "unexpected exclam modifier" 1>&2 !}) 77 .endif 78 79 # Irrelevant assignment modifiers are skipped as well. 80 .if 0 && ${1 2 3:L:@i@${FIRST::?=$i}@} 81 .endif 82 .if 0 && ${1 2 3:L:@i@${LAST::=$i}@} 83 .endif 84 .if 0 && ${1 2 3:L:@i@${APPENDED::+=$i}@} 85 .endif 86 .if 0 && ${echo.1 echo.2 echo.3:L:@i@${RAN::!=${i:C,.*,&; & 1>\&2,:S,., ,g}}@} 87 .endif 88 .if defined(FIRST) || defined(LAST) || defined(APPENDED) || defined(RAN) 89 . warning first=${FIRST} last=${LAST} appended=${APPENDED} ran=${RAN} 90 .endif 91 92 # The || operator: 93 94 .if 1 || ${echo "unexpected or" 1>&2 :L:sh} 95 .endif 96 97 .if 0 || ${echo "expected or" 1>&2 :L:sh} 98 .endif 99 100 .if 1 || exists(nonexistent${echo "unexpected or exists" 1>&2 :L:sh}) 101 .endif 102 103 .if 0 || exists(nonexistent${echo "expected or exists" 1>&2 :L:sh}) 104 .endif 105 106 .if 1 || empty(${echo "unexpected or empty" 1>&2 :L:sh}) 107 .endif 108 109 .if 0 || empty(${echo "expected or empty" 1>&2 :L:sh}) 110 .endif 111 112 # Unreachable nested conditions are skipped completely as well. 113 114 .if 0 115 . if ${echo "unexpected nested and" 1>&2 :L:sh} 116 . endif 117 .endif 118 119 .if 1 120 .elif ${echo "unexpected nested or" 1>&2 :L:sh} 121 .endif 122 123 # make sure these do not cause complaint 124 #.MAKEFLAGS: -dc 125 126 # TODO: Rewrite this whole section and check all the conditions and variables. 127 # Several of the assumptions are probably wrong here. 128 # TODO: replace 'x=' with '.info' or '.error'. 129 V42= 42 130 iV1= ${V42} 131 iV2= ${V66} 132 133 .if defined(V42) && ${V42} > 0 134 x= Ok 135 .else 136 x= Fail 137 .endif 138 x!= echo 'defined(V42) && $${V42} > 0: $x' >&2; echo 139 140 # With cond.c 1.76 from 2020-07-03, the following condition triggered a 141 # warning: "String comparison operator should be either == or !=". 142 # This was because the variable expression ${iV2} was defined, but the 143 # contained variable V66 was undefined. The left-hand side of the comparison 144 # therefore evaluated to the string "${V66}", which is obviously not a number. 145 # 146 # This was fixed in cond.c 1.79 from 2020-07-09 by not evaluating irrelevant 147 # comparisons. Instead, they are only parsed and then discarded. 148 # 149 # At that time, there was not enough debug logging to see the details in the 150 # -dA log. To actually see it, add debug logging at the beginning and end of 151 # Var_Parse. 152 .if defined(V66) && ( ${iV2} < ${V42} ) 153 x= Fail 154 .else 155 x= Ok 156 .endif 157 # XXX: This condition doesn't match the one above. The quotes are missing 158 # above. This is a crucial detail since without quotes, the variable 159 # expression ${iV2} evaluates to "${V66}", and with quotes, it evaluates to "" 160 # since undefined variables are allowed and expand to an empty string. 161 x!= echo 'defined(V66) && ( "$${iV2}" < $${V42} ): $x' >&2; echo 162 163 .if 1 || ${iV1} < ${V42} 164 x= Ok 165 .else 166 x= Fail 167 .endif 168 x!= echo '1 || $${iV1} < $${V42}: $x' >&2; echo 169 170 # With cond.c 1.76 from 2020-07-03, the following condition triggered a 171 # warning: "String comparison operator should be either == or !=". 172 # This was because the variable expression ${iV2} was defined, but the 173 # contained variable V66 was undefined. The left-hand side of the comparison 174 # therefore evaluated to the string "${V66}", which is obviously not a number. 175 # 176 # This was fixed in cond.c 1.79 from 2020-07-09 by not evaluating irrelevant 177 # comparisons. Instead, they are only parsed and then discarded. 178 # 179 # At that time, there was not enough debug logging to see the details in the 180 # -dA log. To actually see it, add debug logging at the beginning and end of 181 # Var_Parse. 182 .if 1 || ${iV2:U2} < ${V42} 183 x= Ok 184 .else 185 x= Fail 186 .endif 187 x!= echo '1 || $${iV2:U2} < $${V42}: $x' >&2; echo 188 189 # the same expressions are fine when the lhs is expanded 190 # ${iV1} expands to 42 191 .if 0 || ${iV1} <= ${V42} 192 x= Ok 193 .else 194 x= Fail 195 .endif 196 x!= echo '0 || $${iV1} <= $${V42}: $x' >&2; echo 197 198 # ${iV2:U2} expands to 2 199 .if 0 || ${iV2:U2} < ${V42} 200 x= Ok 201 .else 202 x= Fail 203 .endif 204 x!= echo '0 || $${iV2:U2} < $${V42}: $x' >&2; echo 205 206 # The right-hand side of the '&&' is irrelevant since the left-hand side 207 # already evaluates to false. Before cond.c 1.79 from 2020-07-09, it was 208 # expanded nevertheless, although with a small modification: undefined 209 # variables may be used in these expressions without generating an error. 210 .if defined(UNDEF) && ${UNDEF} != "undefined" 211 . error 212 .endif 213 214 all: 215
Indexes created Mon Oct 20 20:10:13 GMT 2025