From 612cee1af9daaef5f2d17c3c613a54e5e4c6bec6 Mon Sep 17 00:00:00 2001
From: raeperd <raeperd117@gmail.com>
Date: Sun, 12 Oct 2025 17:43:59 +0900
Subject: [PATCH] feat: auto-detect go.mod when no version inputs specified

- Add unit tests for auto-detection behavior
- Implement go.mod auto-detection in resolveVersionInput()
- Explicit inputs still take precedence over auto-detection

Related issue: #523
---
 __tests__/setup-go.test.ts | 25 +++++++++++++++++++++++++
 dist/setup/index.js        |  3 +++
 src/main.ts                |  4 ++++
 3 files changed, 32 insertions(+)

diff --git a/__tests__/setup-go.test.ts b/__tests__/setup-go.test.ts
index b89c08f..7dc3c03 100644
--- a/__tests__/setup-go.test.ts
+++ b/__tests__/setup-go.test.ts
@@ -1090,4 +1090,29 @@ use .
     expect(vars).toStrictEqual({GOTOOLCHAIN: 'local'});
     expect(process.env).toHaveProperty('GOTOOLCHAIN', 'local');
   });
+
+  describe('auto-detect go.mod', () => {
+    it('uses go.mod from workspace root when no inputs provided', async () => {
+      existsSpy.mockImplementation((filePath: string) => {
+        return filePath === 'go.mod';
+      });
+      readFileSpy.mockImplementation(() =>
+        Buffer.from('module test\n\ngo 1.20')
+      );
+
+      await main.run();
+
+      expect(logSpy).toHaveBeenCalledWith('Setup go version spec 1.20');
+    });
+
+    it('uses pre-installed Go when no inputs and no go.mod exists', async () => {
+      existsSpy.mockImplementation(() => false);
+
+      await main.run();
+
+      expect(logSpy).toHaveBeenCalledWith(
+        '[warning]go-version input was not specified. The action will try to use pre-installed version.'
+      );
+    });
+  });
 });
diff --git a/dist/setup/index.js b/dist/setup/index.js
index 96f4ef9..3290c12 100644
--- a/dist/setup/index.js
+++ b/dist/setup/index.js
@@ -94902,6 +94902,9 @@ function resolveVersionInput() {
         }
         version = installer.parseGoVersionFile(versionFilePath);
     }
+    if (!version && fs_1.default.existsSync('go.mod')) {
+        version = installer.parseGoVersionFile('go.mod');
+    }
     return version;
 }
 function setGoToolchain() {
diff --git a/src/main.ts b/src/main.ts
index 26939ee..9ad747f 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -160,6 +160,10 @@ function resolveVersionInput(): string {
     version = installer.parseGoVersionFile(versionFilePath);
   }
 
+  if (!version && fs.existsSync('go.mod')) {
+    version = installer.parseGoVersionFile('go.mod');
+  }
+
   return version;
 }