parser, cgen: fix option variable error (fix vlang#17460) (vlang#17479)

Author: yuyi98

vlib/v/gen/c/assign.v

@@ -103,8 +103,10 @@ fn (mut g Gen) assign_stmt(node_ ast.AssignStmt) {
 	mut return_type := ast.void_type
 	is_decl := node.op == .decl_assign
 	g.assign_op = node.op
+	g.inside_assign = true
 	defer {
 		g.assign_op = .unknown
+		g.inside_assign = false
 	}
 	op := if is_decl { token.Kind.assign } else { node.op }
 	right_expr := node.right[0]
@@ -597,7 +599,8 @@ fn (mut g Gen) assign_stmt(node_ ast.AssignStmt) {
 						if val.is_auto_deref_var() {
 							g.write('*')
 						}
-						if var_type.has_flag(.option) || gen_or {
+						if (var_type.has_flag(.option) && val !in [ast.Ident, ast.SelectorExpr])
+							|| gen_or {
 							g.expr_with_opt_or_block(val, val_type, left, var_type)
 						} else if val is ast.ArrayInit {
 							g.array_init(val, c_name(ident.name))

vlib/v/gen/c/cgen.v

@@ -120,6 +120,7 @@ mut:
 	inside_ternary            int  // ?: comma separated statements on a single line
 	inside_map_postfix        bool // inside map++/-- postfix expr
 	inside_map_infix          bool // inside map<</+=/-= infix expr
+	inside_assign             bool
 	inside_map_index          bool
 	inside_opt_or_res         bool
 	inside_opt_data           bool
@@ -4123,7 +4124,7 @@ fn (mut g Gen) ident(node ast.Ident) {
 				styp := g.base_type(node.info.typ)
 				g.write('(*(${styp}*)${name}.data)')
 			}
-			if node.or_expr.kind != .absent {
+			if node.or_expr.kind != .absent && !(g.inside_assign && !g.is_assign_lhs) {
 				stmt_str := g.go_before_stmt(0).trim_space()
 				g.empty_line = true
 				g.or_block(name, node.or_expr, node.info.typ)

vlib/v/gen/c/if.v

@@ -252,6 +252,7 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 		} else if branch.cond is ast.IfGuardExpr {
 			mut var_name := guard_vars[i]
 			mut short_opt := false
+			g.left_is_opt = true
 			if var_name == '' {
 				short_opt = true // we don't need a further tmp, so use the one we'll get later
 				var_name = g.new_tmp_var()

vlib/v/parser/if_match.v

@@ -113,7 +113,7 @@ fn (mut p Parser) if_expr(is_comptime bool) ast.IfExpr {
 			p.check(.decl_assign)
 			comments << p.eat_comments()
 			expr := p.expr(0)
-			if expr !in [ast.CallExpr, ast.IndexExpr, ast.PrefixExpr, ast.SelectorExpr] {
+			if expr !in [ast.CallExpr, ast.IndexExpr, ast.PrefixExpr, ast.SelectorExpr, ast.Ident] {
 				p.error_with_pos('if guard condition expression is illegal, it should return an Option',
 					expr.pos())
 			}

vlib/v/tests/option_var_2_test.v

@@ -0,0 +1,26 @@
+struct Foo {
+	name ?string
+}
+
+fn test_option_var() {
+	foo := Foo{}
+	other := foo.name
+
+	println(typeof(other).name)
+	if name := other {
+		println('with name: ${name}')
+		assert false
+	} else {
+		println('without name')
+		assert true
+	}
+
+	mut counter := 0
+	val := other or {
+		counter++
+		'default'
+	}
+
+	assert val == 'default'
+	assert counter == 1
+}