[BUG] Nested struct with required field is not failing on decode

[gaaral]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

The decoder doesn't fail if a required property of the nested struct is not populated.

Expected Behavior

The decoder should throw an error if a required field is missing in the nested struct.

Steps To Reproduce

Test

func TestDecoder(t *testing.T) {
	type Bar struct {
		Baz string `json:"baz,required"`
		Qux string `json:"qux"`
	}

	type Foo struct {
		Field string `json:"field,required"`
		Bars  []Bar  `json:"bars"`
	}

	t.Run("should test nested struct", func(t *testing.T) {
		payload := map[string][]string{
			"field":      {"foo"},
			"bars.0.baz": {"baz"},
		}

		d := schema.NewDecoder()
		d.SetAliasTag("json")

		var foo Foo
		err := d.Decode(&foo, payload)

		assert.Nil(t, err)
	})

	t.Run("should fail on bars.0.baz", func(t *testing.T) {
		payload := map[string][]string{
			"field":      {"foo"},
			"bars.0.qux": {"qux"},
		}

		d := schema.NewDecoder()
		d.SetAliasTag("json")

		var foo Foo
		err := d.Decode(&foo, payload)

		assert.Error(t, err, "bars.0.baz is empty")
		assert.NotNil(t, err)
	})

	t.Run("should fail for field", func(t *testing.T) {
		payload := map[string][]string{
			"bars.0.baz": {"baz"},
		}

		d := schema.NewDecoder()
		d.SetAliasTag("json")

		var foo Foo
		err := d.Decode(&foo, payload)

		assert.Error(t, err, "field is empty")
		assert.NotNil(t, err)
	})
}

Result

=== RUN   TestDecoder
=== RUN   TestDecoder/should_test_nested_struct
=== RUN   TestDecoder/should_fail_on_bars.0.baz
    api_test.go:291: 
        	Error Trace:
        	Error:      	An error is expected but got nil.
        	Test:       	TestDecoder/should_fail_on_bars.0.baz
        	Messages:   	bars.0.baz is empty
    api_test.go:292: 
        	Error Trace:
        	Error:      	Expected value not to be nil.
        	Test:       	TestDecoder/should_fail_on_bars.0.baz
=== RUN   TestDecoder/should_fail_for_field
--- FAIL: TestDecoder (0.00s)
    --- PASS: TestDecoder/should_test_nested_struct (0.00s)
    --- FAIL: TestDecoder/should_fail_on_bars.0.baz (0.00s)

    --- PASS: TestDecoder/should_fail_for_field (0.00s)

FAIL

Anything else?

No response

[jaitaiwan]

Really appreciate being given tests to add to the repo. I'm concerned that in fixing it, it might break existing user's implementations so the fix for this will probably have to be done in a major version