fix(api): keep milestone due date when it is omitted in edit request (#39869) (#39921)

Backport https://github.com/go-gitea/gitea/pull/39869

`PATCH /repos/{owner}/{repo}/milestones/{id}` always overwrote the due
date with `due_on`, so a request that only changed other fields, such as
`{"state": "closed"}`, silently removed it.

The due date is now kept when `due_on` is omitted, and `"due_on": null`
or `"due_on": ""` remove it.

Only the milestone fix is backported. The issue and pull request
deadline changes of https://github.com/go-gitea/gitea/pull/39869 build
on https://github.com/go-gitea/gitea/pull/38677, which isn't on v28.

modules/optional/serialization.go

@@ -4,17 +4,28 @@
 package optional
 
 import (
+	"reflect"
+
 	"gitea.dev/modules/json"
 
 	"go.yaml.in/yaml/v4"
 )
 
+func (o *Option[T]) assignUnmarshalledValue(v *T) {
+	if reflect.TypeFor[T]().Kind() == reflect.Pointer && v == nil {
+		var zero T
+		*o = Some[T](zero)
+	} else {
+		*o = FromPtr(v)
+	}
+}
+
 func (o *Option[T]) UnmarshalJSON(data []byte) error {
 	var v *T
 	if err := json.Unmarshal(data, &v); err != nil {
 		return err
 	}
-	*o = FromPtr(v)
+	o.assignUnmarshalledValue(v)
 	return nil
 }
 
@@ -31,7 +42,7 @@ func (o *Option[T]) UnmarshalYAML(value *yaml.Node) error {
 	if err := value.Decode(&v); err != nil {
 		return err
 	}
-	*o = FromPtr(v)
+	o.assignUnmarshalledValue(v)
 	return nil
 }
 

modules/optional/serialization_test.go

@@ -6,6 +6,7 @@ package optional_test
 import (
 	std_json "encoding/json" //nolint:depguard // for testing purpose
 	"testing"
+	"time"
 
 	"gitea.dev/modules/json"
 	"gitea.dev/modules/optional"
@@ -28,6 +29,14 @@ type testSerializationStruct struct {
 	OptTwoString optional.Option[string] `json:"optional_two_string" yaml:"optional_two_string"`
 }
 
+type testSerializationNullValue struct {
+	OptString optional.Option[string] `json:"opt_null,omitempty" yaml:"opt_null,omitempty"`
+}
+
+type testSerializationNullPointer struct {
+	OptNull optional.Option[*time.Time] `json:"opt_null,omitempty" yaml:"opt_null,omitempty"`
+}
+
 func TestOptionalToJson(t *testing.T) {
 	tests := []struct {
 		name string
@@ -63,6 +72,32 @@ func TestOptionalToJson(t *testing.T) {
 			assert.Equal(t, tc.want, string(b), "std json module returned unexpected")
 		})
 	}
+
+	t.Run("NullValue", func(t *testing.T) {
+		var v1 testSerializationNullValue
+		err := json.Unmarshal([]byte(`{"opt_null":null}`), &v1)
+		assert.NoError(t, err)
+		assert.False(t, v1.OptString.Has())
+	})
+
+	t.Run("NullPointer", func(t *testing.T) {
+		var v1 testSerializationNullPointer
+		err := json.Unmarshal([]byte(`{"opt_null":null}`), &v1)
+		assert.NoError(t, err)
+		assert.True(t, v1.OptNull.Has())
+		assert.Nil(t, v1.OptNull.Value())
+
+		var v2 testSerializationNullPointer
+		err = std_json.Unmarshal([]byte(`{}`), &v2)
+		assert.NoError(t, err)
+		assert.False(t, v2.OptNull.Has())
+
+		var v3 testSerializationNullPointer
+		err = std_json.Unmarshal([]byte(`{"opt_null":"2006-01-02T15:04:05Z"}`), &v3)
+		assert.NoError(t, err)
+		assert.True(t, v3.OptNull.Has())
+		assert.NotNil(t, v3.OptNull.Value())
+	})
 }
 
 func TestOptionalFromJson(t *testing.T) {

modules/structs/issue_milestone.go

@@ -5,6 +5,8 @@ package structs
 
 import (
 	"time"
+
+	"gitea.dev/modules/optional"
 )
 
 // Milestone milestone is a collection of issues on one repository
@@ -54,6 +56,7 @@ type EditMilestoneOption struct {
 	// State indicates the updated state of the milestone
 	// enum: ["open","closed"]
 	State *string `json:"state"`
-	// Deadline is the updated due date for the milestone
-	Deadline *time.Time `json:"due_on"`
+	// Deadline is the due date for the milestone, use null or empty string to remove the deadline
+	// swagger:strfmt date-time
+	Deadline optional.Option[*string] `json:"due_on,omitzero"`
 }