Create annotations where exceptions were thrown

src/utils/git.ts

@@ -0,0 +1,22 @@
+import * as core from '@actions/core'
+import exec from './exec'
+
+export async function listFiles(): Promise<string[]> {
+  core.startGroup('Listing all files tracked by git')
+  let output = ''
+  try {
+    output = (await exec('git', ['ls-files', '-z'])).stdout
+  } finally {
+    fixStdOutNullTermination()
+    core.endGroup()
+  }
+
+  return output.split('\u0000').filter(s => s.length > 0)
+}
+
+function fixStdOutNullTermination(): void {
+  // Previous command uses NULL as delimiters and output is printed to stdout.
+  // We have to make sure next thing written to stdout will start on new line.
+  // Otherwise things like ::set-output wouldn't work.
+  core.info('')
+}