feat(skills): implement linking for agent skills (#18295)

packages/cli/src/utils/skillUtils.test.ts

@@ -8,7 +8,7 @@ import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 import * as fs from 'node:fs/promises';
 import * as path from 'node:path';
 import * as os from 'node:os';
-import { installSkill } from './skillUtils.js';
+import { installSkill, linkSkill } from './skillUtils.js';
 
 describe('skillUtils', () => {
   let tempDir: string;
@@ -24,6 +24,94 @@ describe('skillUtils', () => {
     vi.restoreAllMocks();
   });
 
+  describe('linkSkill', () => {
+    it('should successfully link from a local directory', async () => {
+      // Create a mock skill directory
+      const mockSkillSourceDir = path.join(tempDir, 'mock-skill-source');
+      const skillSubDir = path.join(mockSkillSourceDir, 'test-skill');
+      await fs.mkdir(skillSubDir, { recursive: true });
+      await fs.writeFile(
+        path.join(skillSubDir, 'SKILL.md'),
+        '---\nname: test-skill\ndescription: test\n---\nbody',
+      );
+
+      const skills = await linkSkill(mockSkillSourceDir, 'workspace', () => {});
+      expect(skills.length).toBe(1);
+      expect(skills[0].name).toBe('test-skill');
+
+      const linkedPath = path.join(tempDir, '.gemini/skills', 'test-skill');
+      const stats = await fs.lstat(linkedPath);
+      expect(stats.isSymbolicLink()).toBe(true);
+
+      const linkTarget = await fs.readlink(linkedPath);
+      expect(path.resolve(linkTarget)).toBe(path.resolve(skillSubDir));
+    });
+
+    it('should overwrite existing skill at destination', async () => {
+      const mockSkillSourceDir = path.join(tempDir, 'mock-skill-source');
+      const skillSubDir = path.join(mockSkillSourceDir, 'test-skill');
+      await fs.mkdir(skillSubDir, { recursive: true });
+      await fs.writeFile(
+        path.join(skillSubDir, 'SKILL.md'),
+        '---\nname: test-skill\ndescription: test\n---\nbody',
+      );
+
+      const targetDir = path.join(tempDir, '.gemini/skills');
+      await fs.mkdir(targetDir, { recursive: true });
+      const existingPath = path.join(targetDir, 'test-skill');
+      await fs.mkdir(existingPath);
+
+      const skills = await linkSkill(mockSkillSourceDir, 'workspace', () => {});
+      expect(skills.length).toBe(1);
+
+      const stats = await fs.lstat(existingPath);
+      expect(stats.isSymbolicLink()).toBe(true);
+    });
+
+    it('should abort linking if consent is rejected', async () => {
+      const mockSkillSourceDir = path.join(tempDir, 'mock-skill-source');
+      const skillSubDir = path.join(mockSkillSourceDir, 'test-skill');
+      await fs.mkdir(skillSubDir, { recursive: true });
+      await fs.writeFile(
+        path.join(skillSubDir, 'SKILL.md'),
+        '---\nname: test-skill\ndescription: test\n---\nbody',
+      );
+
+      const requestConsent = vi.fn().mockResolvedValue(false);
+
+      await expect(
+        linkSkill(mockSkillSourceDir, 'workspace', () => {}, requestConsent),
+      ).rejects.toThrow('Skill linking cancelled by user.');
+
+      expect(requestConsent).toHaveBeenCalled();
+
+      // Verify it was NOT linked
+      const linkedPath = path.join(tempDir, '.gemini/skills', 'test-skill');
+      const exists = await fs.lstat(linkedPath).catch(() => null);
+      expect(exists).toBeNull();
+    });
+
+    it('should throw error if multiple skills with same name are discovered', async () => {
+      const mockSkillSourceDir = path.join(tempDir, 'mock-skill-source');
+      const skillDir1 = path.join(mockSkillSourceDir, 'skill1');
+      const skillDir2 = path.join(mockSkillSourceDir, 'skill2');
+      await fs.mkdir(skillDir1, { recursive: true });
+      await fs.mkdir(skillDir2, { recursive: true });
+      await fs.writeFile(
+        path.join(skillDir1, 'SKILL.md'),
+        '---\nname: duplicate-skill\ndescription: desc1\n---\nbody1',
+      );
+      await fs.writeFile(
+        path.join(skillDir2, 'SKILL.md'),
+        '---\nname: duplicate-skill\ndescription: desc2\n---\nbody2',
+      );
+
+      await expect(
+        linkSkill(mockSkillSourceDir, 'workspace', () => {}),
+      ).rejects.toThrow('Duplicate skill name "duplicate-skill" found');
+    });
+  });
+
   it('should successfully install from a .skill file', async () => {
     const skillPath = path.join(projectRoot, 'weather-skill.skill');
 

packages/cli/src/utils/skillUtils.ts

@@ -186,6 +186,75 @@ export async function installSkill(
   }
 }
 
+/**
+ * Central logic for linking a skill from a local path via symlink.
+ */
+export async function linkSkill(
+  source: string,
+  scope: 'user' | 'workspace',
+  onLog: (msg: string) => void,
+  requestConsent: (
+    skills: SkillDefinition[],
+    targetDir: string,
+  ) => Promise<boolean> = () => Promise.resolve(true),
+): Promise<Array<{ name: string; location: string }>> {
+  const sourcePath = path.resolve(source);
+
+  onLog(`Searching for skills in ${sourcePath}...`);
+  const skills = await loadSkillsFromDir(sourcePath);
+
+  if (skills.length === 0) {
+    throw new Error(
+      `No valid skills found in "${sourcePath}". Ensure a SKILL.md file exists with valid frontmatter.`,
+    );
+  }
+
+  // Check for internal name collisions
+  const seenNames = new Map<string, string>();
+  for (const skill of skills) {
+    if (seenNames.has(skill.name)) {
+      throw new Error(
+        `Duplicate skill name "${skill.name}" found at multiple locations:\n  - ${seenNames.get(skill.name)}\n  - ${skill.location}`,
+      );
+    }
+    seenNames.set(skill.name, skill.location);
+  }
+
+  const workspaceDir = process.cwd();
+  const storage = new Storage(workspaceDir);
+  const targetDir =
+    scope === 'workspace'
+      ? storage.getProjectSkillsDir()
+      : Storage.getUserSkillsDir();
+
+  if (!(await requestConsent(skills, targetDir))) {
+    throw new Error('Skill linking cancelled by user.');
+  }
+
+  await fs.mkdir(targetDir, { recursive: true });
+
+  const linkedSkills: Array<{ name: string; location: string }> = [];
+
+  for (const skill of skills) {
+    const skillName = skill.name;
+    const skillSourceDir = path.dirname(skill.location);
+    const destPath = path.join(targetDir, skillName);
+
+    const exists = await fs.lstat(destPath).catch(() => null);
+    if (exists) {
+      onLog(
+        `Skill "${skillName}" already exists at destination. Overwriting...`,
+      );
+      await fs.rm(destPath, { recursive: true, force: true });
+    }
+
+    await fs.symlink(skillSourceDir, destPath, 'dir');
+    linkedSkills.push({ name: skillName, location: destPath });
+  }
+
+  return linkedSkills;
+}
+
 /**
  * Central logic for uninstalling a skill by name.
  */