Make default version explicit (#12)

README.md

@@ -7,7 +7,7 @@ Install and setup [buf](https://github.com/bufbuild/buf) for use in other action
 Refer to the [action.yml](https://github.com/bufbuild/buf-setup-action/blob/main/action.yml)
 to see all of the action parameters.
 
-If `version` is unspecified, it will be defaulted to `latest`.
+If `version` is unspecified, the default value is set to the latest `buf` version:
 
 ```yaml
 steps:
@@ -16,6 +16,28 @@ steps:
   - run: buf --version
 ```
 
+If you want to pin to a specific version, vou can explicitly set it like so:
+
+```yaml
+steps:
+  - uses: actions/checkout@v2
+  - uses: bufbuild/buf-setup-action@v0.4.0
+    with:
+      version: '0.56.0'
+  - run: buf --version
+```
+
+If you want to explicitly set `buf` to its latest release, vou can set it like so:
+
+```yaml
+steps:
+  - uses: actions/checkout@v2
+  - uses: bufbuild/buf-setup-action@v0.4.0
+    with:
+      version: 'latest'
+  - run: buf --version
+```
+
 The `buf-setup` action is commonly used by the other `buf` actions,
 such as [buf-breaking][1], [buf-lint][2], and [buf-push][3].
 

action.yml

@@ -7,7 +7,7 @@ branding:
 inputs:
   version:
     description: 'The version of buf to setup.'
-    default: 'latest'
+    default: '0.56.0'
 runs:
   using: 'node12'
   main: './dist/main.js'

src/run.ts

@@ -42,10 +42,11 @@ export async function run(): Promise<void> {
 // runSetup runs the buf-setup action, and returns
 // a non-empty error if it fails.
 async function runSetup(): Promise<null|Error> {
-    let version = core.getInput('version');
+    const version = core.getInput('version');
     if (version === '') {
-        // If version is not provided, default to 'latest'.
-        version = 'latest'
+        return {
+            message: 'a version was not provided'
+        };
     }
 
     core.info(`Setting up buf version "${version}"`);