cond-short.mk revision 1.15
1 # $NetBSD: cond-short.mk,v 1.15 2020/12/01 19:37:23 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 # The && operator. 18 19 .if 0 && ${echo "unexpected and" 1>&2 :L:sh} 20 .endif 21 22 .if 1 && ${echo "expected and" 1>&2 :L:sh} 23 .endif 24 25 .if 0 && exists(nonexistent${echo "unexpected and exists" 1>&2 :L:sh}) 26 .endif 27 28 .if 1 && exists(nonexistent${echo "expected and exists" 1>&2 :L:sh}) 29 .endif 30 31 .if 0 && empty(${echo "unexpected and empty" 1>&2 :L:sh}) 32 .endif 33 34 .if 1 && empty(${echo "expected and empty" 1>&2 :L:sh}) 35 .endif 36 37 # "VAR U11" is not evaluated; it was evaluated before 2020-07-02. 38 # The whole !empty condition is only parsed and then discarded. 39 VAR= ${VAR${:U11${echo "unexpected VAR U11" 1>&2 :L:sh}}} 40 VAR13= ${VAR${:U12${echo "unexpected VAR13" 1>&2 :L:sh}}} 41 .if 0 && !empty(VAR${:U13${echo "unexpected U13 condition" 1>&2 :L:sh}}) 42 .endif 43 44 VAR= ${VAR${:U21${echo "unexpected VAR U21" 1>&2 :L:sh}}} 45 VAR23= ${VAR${:U22${echo "expected VAR23" 1>&2 :L:sh}}} 46 .if 1 && !empty(VAR${:U23${echo "expected U23 condition" 1>&2 :L:sh}}) 47 .endif 48 VAR= # empty again, for the following tests 49 50 # The :M modifier is only parsed, not evaluated. 51 # Before 2020-07-02, it was wrongly evaluated. 52 .if 0 && !empty(VAR:M${:U${echo "unexpected M pattern" 1>&2 :L:sh}}) 53 .endif 54 55 .if 1 && !empty(VAR:M${:U${echo "expected M pattern" 1>&2 :L:sh}}) 56 .endif 57 58 .if 0 && !empty(VAR:S,from,${:U${echo "unexpected S modifier" 1>&2 :L:sh}},) 59 .endif 60 61 .if 0 && !empty(VAR:C,from,${:U${echo "unexpected C modifier" 1>&2 :L:sh}},) 62 .endif 63 64 .if 0 && !empty("" == "" :? ${:U${echo "unexpected ? modifier" 1>&2 :L:sh}} :) 65 .endif 66 67 .if 0 && !empty(VAR:old=${:U${echo "unexpected = modifier" 1>&2 :L:sh}}) 68 .endif 69 70 .if 0 && !empty(1 2 3:L:@var@${:U${echo "unexpected @ modifier" 1>&2 :L:sh}}@) 71 .endif 72 73 .if 0 && !empty(:U${:!echo "unexpected exclam modifier" 1>&2 !}) 74 .endif 75 76 # Irrelevant assignment modifiers are skipped as well. 77 .if 0 && ${1 2 3:L:@i@${FIRST::?=$i}@} 78 .endif 79 .if 0 && ${1 2 3:L:@i@${LAST::=$i}@} 80 .endif 81 .if 0 && ${1 2 3:L:@i@${APPENDED::+=$i}@} 82 .endif 83 .if 0 && ${echo.1 echo.2 echo.3:L:@i@${RAN::!=${i:C,.*,&; & 1>\&2,:S,., ,g}}@} 84 .endif 85 .if defined(FIRST) || defined(LAST) || defined(APPENDED) || defined(RAN) 86 . warning first=${FIRST} last=${LAST} appended=${APPENDED} ran=${RAN} 87 .endif 88 89 # The || operator. 90 91 .if 1 || ${echo "unexpected or" 1>&2 :L:sh} 92 .endif 93 94 .if 0 || ${echo "expected or" 1>&2 :L:sh} 95 .endif 96 97 .if 1 || exists(nonexistent${echo "unexpected or exists" 1>&2 :L:sh}) 98 .endif 99 100 .if 0 || exists(nonexistent${echo "expected or exists" 1>&2 :L:sh}) 101 .endif 102 103 .if 1 || empty(${echo "unexpected or empty" 1>&2 :L:sh}) 104 .endif 105 106 .if 0 || empty(${echo "expected or empty" 1>&2 :L:sh}) 107 .endif 108 109 # Unreachable nested conditions are skipped completely as well. 110 111 .if 0 112 . if ${echo "unexpected nested and" 1>&2 :L:sh} 113 . endif 114 .endif 115 116 .if 1 117 .elif ${echo "unexpected nested or" 1>&2 :L:sh} 118 .endif 119 120 # make sure these do not cause complaint 121 #.MAKEFLAGS: -dc 122 123 # TODO: Rewrite this whole section and check all the conditions and variables. 124 # Several of the assumptions are probably wrong here. 125 # TODO: replace 'x=' with '.info' or '.error'. 126 V42= 42 127 iV1= ${V42} 128 iV2= ${V66} 129 130 .if defined(V42) && ${V42} > 0 131 x= Ok 132 .else 133 x= Fail 134 .endif 135 x!= echo 'defined(V42) && $${V42} > 0: $x' >&2; echo 136 137 # With cond.c 1.76 from 2020-07-03, the following condition triggered a 138 # warning: "String comparison operator should be either == or !=". 139 # This was because the variable expression ${iV2} was defined, but the 140 # contained variable V66 was undefined. The left-hand side of the comparison 141 # therefore evaluated to the string "${V66}", which is obviously not a number. 142 # 143 # This was fixed in cond.c 1.79 from 2020-07-09 by not evaluating irrelevant 144 # comparisons. Instead, they are only parsed and then discarded. 145 # 146 # At that time, there was not enough debug logging to see the details in the 147 # -dA log. To actually see it, add debug logging at the beginning and end of 148 # Var_Parse. 149 .if defined(V66) && ( ${iV2} < ${V42} ) 150 x= Fail 151 .else 152 x= Ok 153 .endif 154 # XXX: This condition doesn't match the one above. The quotes are missing 155 # above. This is a crucial detail since without quotes, the variable 156 # expression ${iV2} evaluates to "${V66}", and with quotes, it evaluates to "" 157 # since undefined variables are allowed and expand to an empty string. 158 x!= echo 'defined(V66) && ( "$${iV2}" < $${V42} ): $x' >&2; echo 159 160 .if 1 || ${iV1} < ${V42} 161 x= Ok 162 .else 163 x= Fail 164 .endif 165 x!= echo '1 || $${iV1} < $${V42}: $x' >&2; echo 166 167 # With cond.c 1.76 from 2020-07-03, the following condition triggered a 168 # warning: "String comparison operator should be either == or !=". 169 # This was because the variable expression ${iV2} was defined, but the 170 # contained variable V66 was undefined. The left-hand side of the comparison 171 # therefore evaluated to the string "${V66}", which is obviously not a number. 172 # 173 # This was fixed in cond.c 1.79 from 2020-07-09 by not evaluating irrelevant 174 # comparisons. Instead, they are only parsed and then discarded. 175 # 176 # At that time, there was not enough debug logging to see the details in the 177 # -dA log. To actually see it, add debug logging at the beginning and end of 178 # Var_Parse. 179 .if 1 || ${iV2:U2} < ${V42} 180 x= Ok 181 .else 182 x= Fail 183 .endif 184 x!= echo '1 || $${iV2:U2} < $${V42}: $x' >&2; echo 185 186 # the same expressions are fine when the lhs is expanded 187 # ${iV1} expands to 42 188 .if 0 || ${iV1} <= ${V42} 189 x= Ok 190 .else 191 x= Fail 192 .endif 193 x!= echo '0 || $${iV1} <= $${V42}: $x' >&2; echo 194 195 # ${iV2:U2} expands to 2 196 .if 0 || ${iV2:U2} < ${V42} 197 x= Ok 198 .else 199 x= Fail 200 .endif 201 x!= echo '0 || $${iV2:U2} < $${V42}: $x' >&2; echo 202 203 # The right-hand side of the '&&' is irrelevant since the left-hand side 204 # already evaluates to false. Before cond.c 1.79 from 2020-07-09, it was 205 # expanded nevertheless, although with a small modification: undefined 206 # variables may be used in these expressions without generating an error. 207 .if defined(UNDEF) && ${UNDEF} != "undefined" 208 . error 209 .endif 210 211 # TODO: Test each modifier to make sure it is skipped when it is irrelevant 212 # for the result. Since this test is already quite long, do that in another 213 # test. 214 215 all: 216 @:;: 217
Indexes created Wed Oct 22 13:09:56 GMT 2025