fix(schema): support Schema#add() with schematype instances with di…

…fferent paths

Fix #9370

lib/schema.js

@@ -875,7 +875,9 @@ Object.defineProperty(Schema.prototype, 'base', {
 
 Schema.prototype.interpretAsType = function(path, obj, options) {
   if (obj instanceof SchemaType) {
-    return obj;
+    const clone = obj.clone();
+    clone.path = path;
+    return clone;
   }
 
   // If this schema has an associated Mongoose object, use the Mongoose object's

test/schema.test.js

@@ -2471,4 +2471,28 @@ describe('schema', function() {
 
     assert.equal(schema.path('arr').caster.instance, 'Mixed');
   });
+
+  it('handles using a schematype when defining a path (gh-9370)', function() {
+    const schema1 = Schema({
+      foo: {
+        type: Number,
+        min: 4,
+        get: get
+      }
+    });
+
+    function get(v) {
+      return Math.floor(v);
+    }
+
+    const schema2 = Schema({
+      bar: schema1.path('foo')
+    });
+
+    const schematype = schema2.path('bar');
+    assert.equal(schematype.path, 'bar');
+    assert.equal(schematype.options.type, Number);
+    assert.equal(schematype.options.min, 4);
+    assert.equal(schematype.options.get, get);
+  });
 });