cgen: fix result/option breaks execution order in if statements (fix #16663) (#16778)

vlib/v/gen/c/if.v

@@ -141,6 +141,17 @@ fn (mut g Gen) need_tmp_var_in_expr(expr ast.Expr) bool {
 	return false
 }
 
+fn (mut g Gen) needs_conds_order(node ast.IfExpr) bool {
+	if node.branches.len > 1 {
+		for branch in node.branches {
+			if g.need_tmp_var_in_expr(branch.cond) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
 fn (mut g Gen) if_expr(node ast.IfExpr) {
 	if node.is_comptime {
 		g.comptime_if(node)
@@ -153,6 +164,7 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 	// (as it used to be done).
 	// Always use this in -autofree, since ?: can have tmp expressions that have to be freed.
 	needs_tmp_var := g.need_tmp_var_in_if(node)
+	needs_conds_order := g.needs_conds_order(node)
 	tmp := if needs_tmp_var { g.new_tmp_var() } else { '' }
 	mut cur_line := ''
 	mut raw_state := false
@@ -224,6 +236,7 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 			}
 		}
 	}
+	mut branch_cond_var_names := []string{}
 	for i, branch in node.branches {
 		if i > 0 {
 			g.write('} else ')
@@ -302,6 +315,39 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 					}
 				}
 			}
+		} else {
+			if i == 0 && node.branches.len > 1 && !needs_tmp_var && needs_conds_order {
+				cond_var_name := g.new_tmp_var()
+				line := g.go_before_stmt(0).trim_space()
+				g.empty_line = true
+				g.write('bool ${cond_var_name} = ')
+				g.expr(branch.cond)
+				g.writeln(';')
+				branch_cond_var_names << cond_var_name
+				g.set_current_pos_as_last_stmt_pos()
+				g.writeln(line)
+				g.writeln('if (${cond_var_name}) {')
+			} else if i > 0 && branch_cond_var_names.len > 0 && !needs_tmp_var && needs_conds_order {
+				cond_var_name := g.new_tmp_var()
+				line := g.go_before_stmt(0)
+				g.empty_line = true
+				g.writeln('bool ${cond_var_name};')
+				branch_cond := branch_cond_var_names.join(' || ')
+				g.writeln('if (!(${branch_cond})) {')
+				g.set_current_pos_as_last_stmt_pos()
+				g.indent++
+				g.write('${cond_var_name} = ')
+				prev_is_autofree := g.is_autofree
+				g.is_autofree = false
+				g.expr(branch.cond)
+				g.is_autofree = prev_is_autofree
+				g.writeln(';')
+				g.indent--
+				g.writeln('}')
+				branch_cond_var_names << cond_var_name
+				g.set_current_pos_as_last_stmt_pos()
+				g.write(line)
+				g.writeln('if (${cond_var_name}) {')
 			} else {
 				mut no_needs_par := false
 				if branch.cond is ast.InfixExpr {
@@ -322,6 +368,7 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 					g.writeln(') {')
 				}
 			}
+		}
 		if needs_tmp_var {
 			prev_expected_cast_type := g.expected_cast_type
 			if node.is_expr

vlib/v/tests/inout/printing_complex_if_exprs_output.out

@@ -0,0 +1,4 @@
+test
+f1
+f2
+-> 02

vlib/v/tests/inout/printing_complex_if_exprs_output.vv

@@ -0,0 +1,38 @@
+fn f1() bool {
+	println('f1')
+	return false
+}
+
+fn f2() bool {
+	println('f2')
+	return true
+}
+
+fn f3() !bool {
+	println('f3')
+	return false
+}
+
+fn f4() bool {
+	println('f4')
+	return true
+}
+
+fn test() ! {
+	println('test')
+	if f1() {
+		println('-> 01')
+	} else if f2() {
+		println('-> 02')
+	} else if f2() && f3()! {
+		println('-> 03')
+	} else if f4() {
+		println('-> 04')
+	} else {
+		println('-> 05')
+	}
+}
+
+fn main() {
+	test() or { panic(err) }
+}