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. 42VAR= ${VAR${:U11${echo "unexpected VAR U11" 1>&2 :L:sh}}} 43VAR13= ${VAR${: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 47VAR= ${VAR${:U21${echo "unexpected VAR U21" 1>&2 :L:sh}}} 48VAR23= ${VAR${:U22${echo "expected VAR23" 1>&2 :L:sh}}} 49.if 1 && !empty(VAR${:U23${echo "expected U23 condition" 1>&2 :L:sh}}) 50.endif 51VAR= # empty again, for the following tests 52 53# The :M modifier is only parsed, not evaluated. 54# Before 2020-07-02, it was wrongly evaluated. 55.if 0 && !empty(VAR:M${: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'. 129V42= 42 130iV1= ${V42} 131iV2= ${V66} 132 133.if defined(V42) && ${V42} > 0 134x= Ok 135.else 136x= Fail 137.endif 138x!= echo 'defined(V42) && $${V42} > 0: $x' >&2; echo 139 140# With cond.c 1.76 from 2020-07-03, the following condition triggered a 141# warning: "String comparison operator should be either == or !=". 142# This was because the variable expression ${iV2} was defined, but the 143# contained variable V66 was undefined. The left-hand side of the comparison 144# therefore evaluated to the string "${V66}", which is obviously not a number. 145# 146# This was fixed in cond.c 1.79 from 2020-07-09 by not evaluating irrelevant 147# comparisons. Instead, they are only parsed and then discarded. 148# 149# At that time, there was not enough debug logging to see the details in the 150# -dA log. To actually see it, add debug logging at the beginning and end of 151# Var_Parse. 152.if defined(V66) && ( ${iV2} < ${V42} ) 153x= Fail 154.else 155x= Ok 156.endif 157# XXX: This condition doesn't match the one above. The quotes are missing 158# above. This is a crucial detail since without quotes, the variable 159# expression ${iV2} evaluates to "${V66}", and with quotes, it evaluates to "" 160# since undefined variables are allowed and expand to an empty string. 161x!= echo 'defined(V66) && ( "$${iV2}" < $${V42} ): $x' >&2; echo 162 163.if 1 || ${iV1} < ${V42} 164x= Ok 165.else 166x= Fail 167.endif 168x!= echo '1 || $${iV1} < $${V42}: $x' >&2; echo 169 170# With cond.c 1.76 from 2020-07-03, the following condition triggered a 171# warning: "String comparison operator should be either == or !=". 172# This was because the variable expression ${iV2} was defined, but the 173# contained variable V66 was undefined. The left-hand side of the comparison 174# therefore evaluated to the string "${V66}", which is obviously not a number. 175# 176# This was fixed in cond.c 1.79 from 2020-07-09 by not evaluating irrelevant 177# comparisons. Instead, they are only parsed and then discarded. 178# 179# At that time, there was not enough debug logging to see the details in the 180# -dA log. To actually see it, add debug logging at the beginning and end of 181# Var_Parse. 182.if 1 || ${iV2:U2} < ${V42} 183x= Ok 184.else 185x= Fail 186.endif 187x!= echo '1 || $${iV2:U2} < $${V42}: $x' >&2; echo 188 189# the same expressions are fine when the lhs is expanded 190# ${iV1} expands to 42 191.if 0 || ${iV1} <= ${V42} 192x= Ok 193.else 194x= Fail 195.endif 196x!= echo '0 || $${iV1} <= $${V42}: $x' >&2; echo 197 198# ${iV2:U2} expands to 2 199.if 0 || ${iV2:U2} < ${V42} 200x= Ok 201.else 202x= Fail 203.endif 204x!= echo '0 || $${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 214all: 215