checker, cgen: fix if define comptime checking

vlib/v/checker/comptime.v

@@ -742,7 +742,15 @@ fn (mut c Checker) comptime_if_cond(mut cond ast.Expr, pos token.Pos) ComptimeBr
 				should_record_ident = true
 				is_user_ident = true
 				ident_name = cond.expr.name
-				return if cond.expr.name in c.pref.compile_defines_all { .eval } else { .skip }
+				return if cond.expr.name in c.pref.compile_defines {
+					.eval
+				} else {
+					if cond.expr.name in c.pref.compile_defines_all {
+						ComptimeBranchSkipState.unknown
+					} else {
+						ComptimeBranchSkipState.skip
+					}
+				}
 			} else {
 				c.error('invalid `\$if` condition', cond.pos)
 			}

vlib/v/gen/c/comptime.v

@@ -511,12 +511,17 @@ fn (mut g Gen) comptime_if_cond(cond ast.Expr, pkg_exist bool) (bool, bool) {
 			return is_cond_true, false
 		}
 		ast.PostfixExpr {
-			ifdef := g.comptime_if_to_ifdef((cond.expr as ast.Ident).name, true) or {
+			dname := (cond.expr as ast.Ident).name
+			ifdef := g.comptime_if_to_ifdef(dname, true) or {
 				verror(err.str())
 				return false, true
 			}
 			g.write('defined(${ifdef})')
-			return true, false
+			if dname in g.pref.compile_defines_all && dname !in g.pref.compile_defines {
+				return false, true
+			} else {
+				return true, false
+			}
 		}
 		ast.InfixExpr {
 			match cond.op {

vlib/v/gen/c/testdata/if_define_check_not_set.out

@@ -0,0 +1,2 @@
+some_define was not passed
+

vlib/v/gen/c/testdata/if_define_check_not_set.vv

@@ -0,0 +1,12 @@
+module main
+
+// vtest vflags: -d some_define=
+
+fn main() {
+	$if some_define ? {
+		println('some_define was passed')
+	} $else {
+		println('some_define was not passed')
+	}
+	println($d('some_define', 'unknown'))
+}

vlib/v/gen/c/testdata/if_define_check_set.out

@@ -0,0 +1,2 @@
+some_define was passed
+true

vlib/v/gen/c/testdata/if_define_check_set.vv

@@ -0,0 +1,12 @@
+module main
+
+// vtest vflags: -d some_define
+
+fn main() {
+	$if some_define ? {
+		println('some_define was passed')
+	} $else {
+		println('some_define was not passed')
+	}
+	println($d('some_define', 'unknown'))
+}

vlib/v/pref/pref.v

@@ -438,6 +438,7 @@ pub fn parse_args_and_show_errors(known_external_commands []string, args []strin
 			'-nofloat' {
 				res.nofloat = true
 				res.compile_defines_all << 'nofloat' // so that `$if nofloat? {` works
+				res.compile_defines << 'nofloat'
 			}
 			'-fast-math' {
 				res.fast_math = true
@@ -1228,11 +1229,10 @@ fn (mut prefs Preferences) parse_define(define string) {
 	prefs.compile_values[dname] = dvalue
 	prefs.compile_defines_all << dname
 	match dvalue {
-		'0' {}
-		'1' {
+		'' {}
+		else {
 			prefs.compile_defines << dname
 		}
-		else {}
 	}
 }