1# $NetBSD: cond-op.mk,v 1.15 2021/12/10 23:12:44 rillig Exp $ 2# 3# Tests for operators like &&, ||, ! in .if conditions. 4# 5# See also: 6# cond-op-and.mk 7# cond-op-not.mk 8# cond-op-or.mk 9# cond-op-parentheses.mk 10 11# In make, && binds more tightly than ||, like in C. 12# If make had the same precedence for both && and ||, like in the shell, 13# the result would be different. 14# If || were to bind more tightly than &&, the result would be different 15# as well. 16.if !(1 || 1 && 0) 17. error 18.endif 19 20# If make were to interpret the && and || operators like the shell, the 21# previous condition would be interpreted as: 22.if (1 || 1) && 0 23. error 24.endif 25 26# The precedence of the ! operator is different from C though. It has a 27# lower precedence than the comparison operators. Negating a condition 28# does not need parentheses. 29# 30# This kind of condition looks so unfamiliar that it doesn't occur in 31# practice. 32.if !"word" == "word" 33. error 34.endif 35 36# This is how the above condition is actually interpreted. 37.if !("word" == "word") 38. error 39.endif 40 41# TODO: Demonstrate that the precedence of the ! and == operators actually 42# makes a difference. There is a simple example for sure, I just cannot 43# wrap my head around it right now. See the truth table generator below 44# for an example that doesn't require much thought. 45 46# This condition is malformed because the '!' on the right-hand side must not 47# appear unquoted. If any, it must be enclosed in quotes. 48# In any case, it is not interpreted as a negation of an unquoted string. 49# See CondParser_String. 50.if "!word" == !word 51. error 52.endif 53 54# Surprisingly, the ampersand and pipe are allowed in bare strings. 55# That's another opportunity for writing confusing code. 56# See CondParser_String, which only has '!' in the list of stop characters. 57.if "a&&b||c" != a&&b||c 58. error 59.endif 60 61# In the following malformed conditions, as soon as the parser sees the '$' 62# after the '0' or the '1', it knows that the condition will be malformed. 63# Therefore there is no point in evaluating the misplaced expression. 64# 65# Before cond.c 1.286 from 2021-12-10, the extra expression was evaluated 66# nevertheless, since CondParser_Or and CondParser_And asked for the expanded 67# next token, even though in this position of the condition, only comparison 68# operators, TOK_AND, TOK_OR or TOK_RPAREN are allowed. 69# 70# 71# 72# 73# 74# 75.undef ERR 76.if 0 ${ERR::=evaluated} 77. error 78.endif 79.if ${ERR:Uundefined} == undefined 80. info A misplaced expression after 0 is not evaluated. 81.endif 82 83.undef ERR 84.if 1 ${ERR::=evaluated} 85. error 86.endif 87.if ${ERR:Uundefined} == undefined 88. info A misplaced expression after 1 is not evaluated. 89.endif 90 91# Just in case that parsing should ever stop on the first error. 92.info Parsing continues until here. 93 94# Demonstration that '&&' has higher precedence than '||'. 95.info A B C => (A || B) && C A || B && C A || (B && C) 96.for a in 0 1 97. for b in 0 1 98. for c in 0 1 99. for r1 in ${ ($a || $b) && $c :?1:0} 100. for r2 in ${ $a || $b && $c :?1:0} 101. for r3 in ${ $a || ($b && $c) :?1:0} 102. info $a $b $c => ${r1} ${r2} ${r3} 103. endfor 104. endfor 105. endfor 106. endfor 107. endfor 108.endfor 109 110# This condition is obviously malformed. It is properly detected and also 111# was properly detected before 2021-01-19, but only because the left hand 112# side of the '&&' evaluated to true. 113.if 1 && 114. error 115.else 116. error 117.endif 118 119# This obviously malformed condition was not detected as such before cond.c 120# 1.238 from 2021-01-19. 121.if 0 && 122. error 123.else 124. error 125.endif 126 127# This obviously malformed condition was not detected as such before cond.c 128# 1.238 from 2021-01-19. 129.if 1 || 130. error 131.else 132. error 133.endif 134 135# This condition is obviously malformed. It is properly detected and also 136# was properly detected before 2021-01-19, but only because the left hand 137# side of the '||' evaluated to false. 138.if 0 || 139. error 140.else 141. error 142.endif 143 144all: 145 @:; 146