fix: add support for pull_request_target event in GitHub Actions workflows (#579)

Add pull_request_target event support to enable Claude Code usage with forked
repositories while maintaining proper security boundaries. This resolves issues
with dependabot PRs and external contributions that require write permissions.

Changes:
- Add pull_request_target to supported GitHub events in context parsing
- Update type definitions to include PullRequestTargetEvent
- Modify IS_PR calculation to detect pull_request_target as PR context
- Add comprehensive test coverage for pull_request_target workflows
- Update documentation to reflect pull_request_target support

The pull_request_target event provides the same payload structure as
pull_request but runs with write permissions from the base repository,
making it ideal for secure automation of external contributions.

Fixes #347

action.yml

@@ -259,7 +259,7 @@ runs:
         GITHUB_EVENT_NAME: ${{ github.event_name }}
         TRIGGER_COMMENT_ID: ${{ github.event.comment.id }}
         CLAUDE_BRANCH: ${{ steps.prepare.outputs.CLAUDE_BRANCH }}
-        IS_PR: ${{ github.event.issue.pull_request != null || github.event_name == 'pull_request_review_comment' }}
+        IS_PR: ${{ github.event.issue.pull_request != null || github.event_name == 'pull_request_target' || github.event_name == 'pull_request_review_comment' }}
         BASE_BRANCH: ${{ steps.prepare.outputs.BASE_BRANCH }}
         CLAUDE_SUCCESS: ${{ steps.claude-code.outputs.conclusion == 'success' }}
         OUTPUT_FILE: ${{ steps.claude-code.outputs.execution_file || '' }}

docs/custom-automations.md

@@ -15,7 +15,7 @@ The action automatically detects which mode to use based on your configuration:
 
 This action supports the following GitHub events ([learn more GitHub event triggers](https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows)):
 
-- `pull_request` - When PRs are opened or synchronized
+- `pull_request` or `pull_request_target` - When PRs are opened or synchronized
 - `issue_comment` - When comments are created on issues or PRs
 - `pull_request_comment` - When comments are made on PR diffs
 - `issues` - When issues are opened or assigned

src/create-prompt/index.ts

@@ -384,6 +384,7 @@ export function getEventTypeAndContext(envVars: PreparedContext): {
       };
 
     case "pull_request":
+    case "pull_request_target":
       return {
         eventType: "PULL_REQUEST",
         triggerContext: eventData.eventAction

src/create-prompt/types.ts

@@ -78,8 +78,7 @@ type IssueLabeledEvent = {
   labelTrigger: string;
 };
 
-type PullRequestEvent = {
-  eventName: "pull_request";
+type PullRequestBaseEvent = {
   eventAction?: string; // opened, synchronize, etc.
   isPR: true;
   prNumber: string;
@@ -87,6 +86,14 @@ type PullRequestEvent = {
   baseBranch?: string;
 };
 
+type PullRequestEvent = PullRequestBaseEvent & {
+  eventName: "pull_request";
+};
+
+type PullRequestTargetEvent = PullRequestBaseEvent & {
+  eventName: "pull_request_target";
+};
+
 // Union type for all possible event types
 export type EventData =
   | PullRequestReviewCommentEvent
@@ -96,7 +103,8 @@ export type EventData =
   | IssueOpenedEvent
   | IssueAssignedEvent
   | IssueLabeledEvent
-  | PullRequestEvent;
+  | PullRequestEvent
+  | PullRequestTargetEvent;
 
 // Combined type with separate eventData field
 export type PreparedContext = CommonFields & {

src/github/context.ts

@@ -174,7 +174,8 @@ export function parseGitHubContext(): GitHubContext {
         isPR: Boolean(payload.issue.pull_request),
       };
     }
-    case "pull_request": {
+    case "pull_request":
+    case "pull_request_target": {
       const payload = context.payload as PullRequestEvent;
       return {
         ...commonFields,

test/pull-request-target.test.ts

@@ -0,0 +1,504 @@
+#!/usr/bin/env bun
+
+import { describe, test, expect } from "bun:test";
+import {
+  getEventTypeAndContext,
+  generatePrompt,
+  generateDefaultPrompt,
+} from "../src/create-prompt";
+import type { PreparedContext } from "../src/create-prompt";
+import type { Mode } from "../src/modes/types";
+
+describe("pull_request_target event support", () => {
+  // Mock tag mode for testing
+  const mockTagMode: Mode = {
+    name: "tag",
+    description: "Tag mode",
+    shouldTrigger: () => true,
+    prepareContext: (context) => ({ mode: "tag", githubContext: context }),
+    getAllowedTools: () => [],
+    getDisallowedTools: () => [],
+    shouldCreateTrackingComment: () => true,
+    generatePrompt: (context, githubData, useCommitSigning) =>
+      generateDefaultPrompt(context, githubData, useCommitSigning),
+    prepare: async () => ({
+      commentId: 123,
+      branchInfo: {
+        baseBranch: "main",
+        currentBranch: "main",
+        claudeBranch: undefined,
+      },
+      mcpConfig: "{}",
+    }),
+  };
+
+  const mockGitHubData = {
+    contextData: {
+      title: "External PR via pull_request_target",
+      body: "This PR comes from a forked repository",
+      author: { login: "external-contributor" },
+      state: "OPEN",
+      createdAt: "2023-01-01T00:00:00Z",
+      additions: 25,
+      deletions: 3,
+      baseRefName: "main",
+      headRefName: "feature-branch",
+      headRefOid: "abc123",
+      commits: {
+        totalCount: 2,
+        nodes: [
+          {
+            commit: {
+              oid: "commit1",
+              message: "Initial feature implementation",
+              author: {
+                name: "External Dev",
+                email: "external@example.com",
+              },
+            },
+          },
+          {
+            commit: {
+              oid: "commit2",
+              message: "Fix typos and formatting",
+              author: {
+                name: "External Dev",
+                email: "external@example.com",
+              },
+            },
+          },
+        ],
+      },
+      files: {
+        nodes: [
+          {
+            path: "src/feature.ts",
+            additions: 20,
+            deletions: 2,
+            changeType: "MODIFIED",
+          },
+          {
+            path: "tests/feature.test.ts",
+            additions: 5,
+            deletions: 1,
+            changeType: "ADDED",
+          },
+        ],
+      },
+      comments: { nodes: [] },
+      reviews: { nodes: [] },
+    },
+    comments: [],
+    changedFiles: [],
+    changedFilesWithSHA: [
+      {
+        path: "src/feature.ts",
+        additions: 20,
+        deletions: 2,
+        changeType: "MODIFIED",
+        sha: "abc123",
+      },
+      {
+        path: "tests/feature.test.ts",
+        additions: 5,
+        deletions: 1,
+        changeType: "ADDED",
+        sha: "abc123",
+      },
+    ],
+    reviewData: { nodes: [] },
+    imageUrlMap: new Map<string, string>(),
+  };
+
+  describe("prompt generation for pull_request_target", () => {
+    test("should generate correct prompt for pull_request_target event", () => {
+      const envVars: PreparedContext = {
+        repository: "owner/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          eventName: "pull_request_target",
+          eventAction: "opened",
+          isPR: true,
+          prNumber: "123",
+        },
+      };
+
+      const prompt = generatePrompt(
+        envVars,
+        mockGitHubData,
+        false,
+        mockTagMode,
+      );
+
+      // Should contain pull request event type and metadata
+      expect(prompt).toContain("<event_type>PULL_REQUEST</event_type>");
+      expect(prompt).toContain("<is_pr>true</is_pr>");
+      expect(prompt).toContain("<pr_number>123</pr_number>");
+      expect(prompt).toContain(
+        "<trigger_context>pull request opened</trigger_context>",
+      );
+
+      // Should contain PR-specific information
+      expect(prompt).toContain(
+        "- src/feature.ts (MODIFIED) +20/-2 SHA: abc123",
+      );
+      expect(prompt).toContain(
+        "- tests/feature.test.ts (ADDED) +5/-1 SHA: abc123",
+      );
+      expect(prompt).toContain("external-contributor");
+      expect(prompt).toContain("<repository>owner/repo</repository>");
+    });
+
+    test("should handle pull_request_target with commit signing disabled", () => {
+      const envVars: PreparedContext = {
+        repository: "owner/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          eventName: "pull_request_target",
+          eventAction: "synchronize",
+          isPR: true,
+          prNumber: "456",
+        },
+      };
+
+      const prompt = generatePrompt(
+        envVars,
+        mockGitHubData,
+        false,
+        mockTagMode,
+      );
+
+      // Should include git commands for non-commit-signing mode
+      expect(prompt).toContain("git push");
+      expect(prompt).toContain(
+        "Always push to the existing branch when triggered on a PR",
+      );
+      expect(prompt).toContain("mcp__github_comment__update_claude_comment");
+
+      // Should not include commit signing tools
+      expect(prompt).not.toContain("mcp__github_file_ops__commit_files");
+    });
+
+    test("should handle pull_request_target with commit signing enabled", () => {
+      const envVars: PreparedContext = {
+        repository: "owner/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          eventName: "pull_request_target",
+          eventAction: "synchronize",
+          isPR: true,
+          prNumber: "456",
+        },
+      };
+
+      const prompt = generatePrompt(envVars, mockGitHubData, true, mockTagMode);
+
+      // Should include commit signing tools
+      expect(prompt).toContain("mcp__github_file_ops__commit_files");
+      expect(prompt).toContain("mcp__github_file_ops__delete_files");
+      expect(prompt).toContain("mcp__github_comment__update_claude_comment");
+
+      // Should not include git command instructions
+      expect(prompt).not.toContain("Use git commands via the Bash tool");
+    });
+
+    test("should treat pull_request_target same as pull_request in prompt generation", () => {
+      const baseContext: PreparedContext = {
+        repository: "owner/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          eventName: "pull_request_target",
+          eventAction: "opened",
+          isPR: true,
+          prNumber: "123",
+        },
+      };
+
+      // Generate prompt for pull_request
+      const pullRequestContext: PreparedContext = {
+        ...baseContext,
+        eventData: {
+          ...baseContext.eventData,
+          eventName: "pull_request",
+          isPR: true,
+          prNumber: "123",
+        },
+      };
+
+      // Generate prompt for pull_request_target
+      const pullRequestTargetContext: PreparedContext = {
+        ...baseContext,
+        eventData: {
+          ...baseContext.eventData,
+          eventName: "pull_request_target",
+          isPR: true,
+          prNumber: "123",
+        },
+      };
+
+      const pullRequestPrompt = generatePrompt(
+        pullRequestContext,
+        mockGitHubData,
+        false,
+        mockTagMode,
+      );
+      const pullRequestTargetPrompt = generatePrompt(
+        pullRequestTargetContext,
+        mockGitHubData,
+        false,
+        mockTagMode,
+      );
+
+      // Both should have the same event type and structure
+      expect(pullRequestPrompt).toContain(
+        "<event_type>PULL_REQUEST</event_type>",
+      );
+      expect(pullRequestTargetPrompt).toContain(
+        "<event_type>PULL_REQUEST</event_type>",
+      );
+
+      expect(pullRequestPrompt).toContain(
+        "<trigger_context>pull request opened</trigger_context>",
+      );
+      expect(pullRequestTargetPrompt).toContain(
+        "<trigger_context>pull request opened</trigger_context>",
+      );
+
+      // Both should contain PR-specific instructions
+      expect(pullRequestPrompt).toContain(
+        "Always push to the existing branch when triggered on a PR",
+      );
+      expect(pullRequestTargetPrompt).toContain(
+        "Always push to the existing branch when triggered on a PR",
+      );
+    });
+
+    test("should handle pull_request_target in agent mode with custom prompt", () => {
+      const envVars: PreparedContext = {
+        repository: "test/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        prompt: "Review this pull_request_target PR for security issues",
+        eventData: {
+          eventName: "pull_request_target",
+          eventAction: "opened",
+          isPR: true,
+          prNumber: "789",
+        },
+      };
+
+      // Use agent mode which passes through the prompt as-is
+      const mockAgentMode: Mode = {
+        name: "agent",
+        description: "Agent mode",
+        shouldTrigger: () => true,
+        prepareContext: (context) => ({
+          mode: "agent",
+          githubContext: context,
+        }),
+        getAllowedTools: () => [],
+        getDisallowedTools: () => [],
+        shouldCreateTrackingComment: () => true,
+        generatePrompt: (context) => context.prompt || "default prompt",
+        prepare: async () => ({
+          commentId: 123,
+          branchInfo: {
+            baseBranch: "main",
+            currentBranch: "main",
+            claudeBranch: undefined,
+          },
+          mcpConfig: "{}",
+        }),
+      };
+
+      const prompt = generatePrompt(
+        envVars,
+        mockGitHubData,
+        false,
+        mockAgentMode,
+      );
+
+      expect(prompt).toBe(
+        "Review this pull_request_target PR for security issues",
+      );
+    });
+
+    test("should handle pull_request_target with no custom prompt", () => {
+      const envVars: PreparedContext = {
+        repository: "test/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          eventName: "pull_request_target",
+          eventAction: "synchronize",
+          isPR: true,
+          prNumber: "456",
+        },
+      };
+
+      const prompt = generatePrompt(
+        envVars,
+        mockGitHubData,
+        false,
+        mockTagMode,
+      );
+
+      // Should generate default prompt structure
+      expect(prompt).toContain("<event_type>PULL_REQUEST</event_type>");
+      expect(prompt).toContain("<pr_number>456</pr_number>");
+      expect(prompt).toContain(
+        "Always push to the existing branch when triggered on a PR",
+      );
+    });
+  });
+
+  describe("pull_request_target vs pull_request behavior consistency", () => {
+    test("should produce identical event processing for both event types", () => {
+      const baseEventData = {
+        eventAction: "opened",
+        isPR: true,
+        prNumber: "100",
+      };
+
+      const pullRequestEvent: PreparedContext = {
+        repository: "owner/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          ...baseEventData,
+          eventName: "pull_request",
+          isPR: true,
+          prNumber: "100",
+        },
+      };
+
+      const pullRequestTargetEvent: PreparedContext = {
+        repository: "owner/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          ...baseEventData,
+          eventName: "pull_request_target",
+          isPR: true,
+          prNumber: "100",
+        },
+      };
+
+      // Both should have identical event type detection
+      const prResult = getEventTypeAndContext(pullRequestEvent);
+      const prtResult = getEventTypeAndContext(pullRequestTargetEvent);
+
+      expect(prResult.eventType).toBe(prtResult.eventType);
+      expect(prResult.triggerContext).toBe(prtResult.triggerContext);
+    });
+
+    test("should handle edge cases in pull_request_target events", () => {
+      // Test with minimal event data
+      const minimalContext: PreparedContext = {
+        repository: "owner/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          eventName: "pull_request_target",
+          isPR: true,
+          prNumber: "1",
+        },
+      };
+
+      const result = getEventTypeAndContext(minimalContext);
+      expect(result.eventType).toBe("PULL_REQUEST");
+      expect(result.triggerContext).toBe("pull request event");
+
+      // Should not throw when generating prompt
+      expect(() => {
+        generatePrompt(minimalContext, mockGitHubData, false, mockTagMode);
+      }).not.toThrow();
+    });
+
+    test("should handle all valid pull_request_target actions", () => {
+      const actions = ["opened", "synchronize", "reopened", "closed", "edited"];
+
+      actions.forEach((action) => {
+        const context: PreparedContext = {
+          repository: "owner/repo",
+          claudeCommentId: "12345",
+          triggerPhrase: "@claude",
+          eventData: {
+            eventName: "pull_request_target",
+            eventAction: action,
+            isPR: true,
+            prNumber: "1",
+          },
+        };
+
+        const result = getEventTypeAndContext(context);
+        expect(result.eventType).toBe("PULL_REQUEST");
+        expect(result.triggerContext).toBe(`pull request ${action}`);
+      });
+    });
+  });
+
+  describe("security considerations for pull_request_target", () => {
+    test("should maintain same prompt structure regardless of event source", () => {
+      // Test that external PRs don't get different treatment in prompts
+      const internalPR: PreparedContext = {
+        repository: "owner/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          eventName: "pull_request",
+          eventAction: "opened",
+          isPR: true,
+          prNumber: "1",
+        },
+      };
+
+      const externalPR: PreparedContext = {
+        repository: "owner/repo",
+        claudeCommentId: "12345",
+        triggerPhrase: "@claude",
+        eventData: {
+          eventName: "pull_request_target",
+          eventAction: "opened",
+          isPR: true,
+          prNumber: "1",
+        },
+      };
+
+      const internalPrompt = generatePrompt(
+        internalPR,
+        mockGitHubData,
+        false,
+        mockTagMode,
+      );
+      const externalPrompt = generatePrompt(
+        externalPR,
+        mockGitHubData,
+        false,
+        mockTagMode,
+      );
+
+      // Should have same tool access patterns
+      expect(
+        internalPrompt.includes("mcp__github_comment__update_claude_comment"),
+      ).toBe(
+        externalPrompt.includes("mcp__github_comment__update_claude_comment"),
+      );
+
+      // Should have same branch handling instructions
+      expect(
+        internalPrompt.includes(
+          "Always push to the existing branch when triggered on a PR",
+        ),
+      ).toBe(
+        externalPrompt.includes(
+          "Always push to the existing branch when triggered on a PR",
+        ),
+      );
+    });
+  });
+});