feat: Add support for sub-issue

github/github.go

@@ -222,6 +222,7 @@ type Client struct {
 	Search             *SearchService
 	SecretScanning     *SecretScanningService
 	SecurityAdvisories *SecurityAdvisoriesService
+	SubIssue           *SubIssueService
 	Teams              *TeamsService
 	Users              *UsersService
 }
@@ -458,6 +459,7 @@ func (c *Client) initialize() {
 	c.Search = (*SearchService)(&c.common)
 	c.SecretScanning = (*SecretScanningService)(&c.common)
 	c.SecurityAdvisories = (*SecurityAdvisoriesService)(&c.common)
+	c.SubIssue = (*SubIssueService)(&c.common)
 	c.Teams = (*TeamsService)(&c.common)
 	c.Users = (*UsersService)(&c.common)
 }

github/strings_test.go

@@ -107,6 +107,7 @@ func TestString(t *testing.T) {
 		{Hook{ID: Ptr(int64(1))}, `github.Hook{ID:1}`},
 		{IssueComment{ID: Ptr(int64(1))}, `github.IssueComment{ID:1}`},
 		{Issue{Number: Ptr(1)}, `github.Issue{Number:1}`},
+		{SubIssue{ID: Ptr(int64(1))}, `github.SubIssue{ID:1}`},
 		{Key{ID: Ptr(int64(1))}, `github.Key{ID:1}`},
 		{Label{ID: Ptr(int64(1)), Name: Ptr("l")}, `github.Label{ID:1, Name:"l"}`},
 		{Organization{ID: Ptr(int64(1))}, `github.Organization{ID:1}`},

github/sub_issue.go

@@ -0,0 +1,146 @@
+// Copyright 2025 The go-github AUTHORS. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package github
+
+import (
+	"context"
+	"fmt"
+)
+
+// SubIssueService handles communication with the sub-issue related
+// methods of the GitHub API.
+//
+// Sub-issues help you group and manage your issues with a parent/child relationship.
+//
+// GitHub API docs: https://docs.github.com/rest/issues/sub-issues
+type SubIssueService service
+
+// SubIssue represents a GitHub sub-issue on a repository.
+// Note: As far as the GitHub API is concerned, every pull request is an issue,
+// but not every issue is a pull request. Some endpoints, events, and webhooks
+// may also return pull requests via this struct. If PullRequestLinks is nil,
+// this is an issue, and if PullRequestLinks is not nil, this is a pull request.
+// The IsPullRequest helper method can be used to check that.
+type SubIssue Issue
+
+func (i SubIssue) String() string {
+	return Stringify(i)
+}
+
+// SubIssueListByIssueOptions specifies the optional parameters to the
+// SubIssueService.ListByIssue method.
+type SubIssueListByIssueOptions struct {
+	IssueListByRepoOptions
+}
+
+// SubIssueRequest represents a request to add, remove, or reprioritize sub-issues.
+type SubIssueRequest struct {
+	SubIssueID    int64  `json:"sub_issue_id"`             // Required: The ID of the sub-issue
+	AfterID       *int64 `json:"after_id,omitempty"`       // Optional: Position after this sub-issue ID
+	BeforeID      *int64 `json:"before_id,omitempty"`      // Optional: Position before this sub-issue ID
+	ReplaceParent *bool  `json:"replace_parent,omitempty"` // Optional: Whether to replace the existing parent
+}
+
+// Remove a sub-issue from the specified repository.
+//
+// GitHub API docs: https://docs.github.com/rest/issues/sub-issues#remove-sub-issue
+//
+//meta:operation DELETE /repos/{owner}/{repo}/issues/{issue_number}/sub_issue
+func (s *SubIssueService) Remove(ctx context.Context, owner, repo string, subIssueNumber int64, subIssue *SubIssueRequest) (*SubIssue, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/issues/%v/sub_issues", owner, repo, subIssueNumber)
+
+	req, err := s.client.NewRequest("DELETE", u, subIssue)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// TODO: remove custom Accept header when this API fully launches.
+	req.Header.Set("Accept", mediaTypeV3)
+
+	si := new(SubIssue)
+	resp, err := s.client.Do(ctx, req, si)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return si, resp, nil
+}
+
+// ListByIssue lists all sub-issues for the specified issue.
+//
+// GitHub API docs: https://docs.github.com/rest/issues/sub-issues#list-sub-issues
+//
+//meta:operation GET /repos/{owner}/{repo}/issues/{issue_number}/sub_issues
+func (s *SubIssueService) ListByIssue(ctx context.Context, owner, repo string, issueNumber int64, opts *IssueListOptions) ([]*SubIssue, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/issues/%d/sub_issues", owner, repo, issueNumber)
+	u, err := addOptions(u, opts)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	req, err := s.client.NewRequest("GET", u, nil)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// TODO: remove custom Accept header when this API fully launches.
+	req.Header.Set("Accept", mediaTypeV3)
+
+	var subIssues []*SubIssue
+	resp, err := s.client.Do(ctx, req, &subIssues)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return subIssues, resp, nil
+}
+
+// Add adds a sub-issue to the specified issue.
+//
+// The sub-issue to be added must belong to the same repository owner as the parent issue.
+// To replace the existing parent of a sub-issue, set replaceParent to true.
+//
+// GitHub API docs: https://docs.github.com/rest/issues/sub-issues#add-sub-issue
+//
+//meta:operation POST /repos/{owner}/{repo}/issues/{issue_number}/sub_issues
+func (s *SubIssueService) Add(ctx context.Context, owner string, repo string, issueNumber int, subIssue *SubIssueRequest) (*SubIssue, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/issues/%v/sub_issues", owner, repo, issueNumber)
+	req, err := s.client.NewRequest("POST", u, subIssue)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	si := new(SubIssue)
+	resp, err := s.client.Do(ctx, req, si)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return si, resp, nil
+}
+
+// Reprioritize changes a sub-issue's priority to a different position in the parent list.
+//
+// Either afterId or beforeId must be specified to determine the new position of the sub-issue.
+//
+// GitHub API docs: https://docs.github.com/rest/issues/sub-issues#reprioritize-sub-issue
+//
+//meta:operation PATCH /repos/{owner}/{repo}/issues/{issue_number}/sub_issues/priority
+func (s *SubIssueService) Reprioritize(ctx context.Context, owner, repo string, issueNumber int64, subIssue *SubIssueRequest) (*SubIssue, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/issues/%d/sub_issues/priority", owner, repo, issueNumber)
+	req, err := s.client.NewRequest("PATCH", u, subIssue)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	si := new(SubIssue)
+	resp, err := s.client.Do(ctx, req, si)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return si, resp, nil
+}