checker: fix external enum value resolution, i.e. enum { enum_value = C.VALUE } (#18401)

vlib/v/ast/table.v

@@ -372,8 +372,9 @@ pub fn (t &Table) find_method_with_embeds(sym &TypeSymbol, method_name string) !
 	}
 }
 
-// find_enum_field_val finds the int value from the enum name and enum field
-pub fn (t &Table) find_enum_field_val(name string, field_ string) i64 {
+// find_enum_field_val finds the possible int value from the enum name and enum field
+// (returns `none` if the value cannot be resolved at compile time)
+pub fn (t &Table) find_enum_field_val(name string, field_ string) ?i64 {
 	mut val := i64(0)
 	enum_decl := t.enum_decls[name]
 	mut enum_vals := []i64{}
@@ -384,6 +385,7 @@ pub fn (t &Table) find_enum_field_val(name string, field_ string) i64 {
 					val = field.expr.val.i64()
 					break
 				}
+				return none
 			} else {
 				if enum_vals.len > 0 {
 					val = enum_vals.last() + 1
@@ -396,6 +398,8 @@ pub fn (t &Table) find_enum_field_val(name string, field_ string) i64 {
 			if field.has_expr {
 				if field.expr is IntegerLiteral {
 					enum_vals << field.expr.val.i64()
+				} else {
+					return none
 				}
 			} else {
 				if enum_vals.len > 0 {

vlib/v/checker/comptime.v

@@ -270,7 +270,9 @@ fn (mut c Checker) eval_comptime_const_expr(expr ast.Expr, nlevel int) ?ast.Comp
 			return c.eval_comptime_const_expr(expr.expr, nlevel + 1)
 		}
 		ast.EnumVal {
-			return c.table.find_enum_field_val(expr.enum_name, expr.val)
+			if val := c.table.find_enum_field_val(expr.enum_name, expr.val) {
+				return val
+			}
 		}
 		ast.SizeOf {
 			s, _ := c.table.type_size(expr.typ)

vlib/v/checker/containers.v

@@ -250,8 +250,11 @@ fn (mut c Checker) array_init(mut node ast.ArrayInit) ast.Type {
 						fixed_size = init_expr.expr.val.int()
 					}
 					ast.EnumVal {
-						fixed_size = c.table.find_enum_field_val(init_expr.expr.enum_name,
+						if val := c.table.find_enum_field_val(init_expr.expr.enum_name,
 							init_expr.expr.val)
+						{
+							fixed_size = val
+						}
 					}
 					else {}
 				}

vlib/v/tests/const_resolution_test.v

@@ -0,0 +1,10 @@
+import gx
+
+const left = gx.align_left
+
+fn test_main() {
+	align := left
+	assert dump(align.str()) == 'left'
+	assert dump(gx.align_left) == gx.align_left
+	assert gx.align_left.str() == 'left'
+}