fix ambiguous embed struct reference

checker/checker.go

@@ -125,6 +125,9 @@ func (v *visitor) IdentifierNode(node *ast.IdentifierNode) reflect.Type {
 		return interfaceType
 	}
 	if t, ok := v.types[node.Value]; ok {
+		if t.Ambiguous {
+			return v.error(node, "ambiguous identifier %v", node.Value)
+		}
 		return t.Type
 	}
 	if !v.strict {

checker/types.go

@@ -209,7 +209,7 @@ func fieldType(ntype reflect.Type, name string) (reflect.Type, bool) {
 			// First check all struct's fields.
 			for i := 0; i < ntype.NumField(); i++ {
 				f := ntype.Field(i)
-				if !f.Anonymous && f.Name == name {
+				if f.Name == name {
 					return f.Type, true
 				}
 			}

conf/types_table.go

@@ -3,8 +3,9 @@ package conf
 import "reflect"
 
 type Tag struct {
-	Type   reflect.Type
-	Method bool
+	Type      reflect.Type
+	Method    bool
+	Ambiguous bool
 }
 
 type TypesTable map[string]Tag
@@ -73,7 +74,11 @@ func FieldsFromStruct(t reflect.Type) TypesTable {
 
 			if f.Anonymous {
 				for name, typ := range FieldsFromStruct(f.Type) {
-					types[name] = typ
+					if _, ok := types[name]; ok {
+						types[name] = Tag{Ambiguous: true}
+					} else {
+						types[name] = typ
+					}
 				}
 			}
 

expr_test.go

@@ -1093,6 +1093,36 @@ func TestEval_exposed_error(t *testing.T) {
 	require.Equal(t, 1, fileError.Line)
 }
 
+func TestIssue105(t *testing.T) {
+	type A struct {
+		Field string
+	}
+	type B struct {
+		Field int
+	}
+	type C struct {
+		A
+		B
+	}
+	type Env struct {
+		C
+	}
+
+	code := `
+		A.Field == '' &&
+		C.A.Field == '' &&
+		B.Field == 0 &&
+		C.B.Field == 0
+	`
+
+	_, err := expr.Compile(code, expr.Env(Env{}))
+	require.NoError(t, err)
+
+	_, err = expr.Compile(`Field == ''`, expr.Env(Env{}))
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "ambiguous identifier Field")
+}
+
 //
 // Mock types
 //