fix: automatically regenerate empty completion cache (#2773)

Fixes #2759

The completion cache validation now checks if the file is empty and
automatically regenerates it. This prevents shell completions from
breaking when the cache file exists but is corrupted or empty.

Previously, NeedsUpdate() only checked file existence and age, but
didn't validate file contents. Empty cache files would be used as-is,
causing 'yay -Pc' to return no output and breaking shell completions.

Changes:
- Add file size check in NeedsUpdate() to detect empty cache files
- Add test case for empty file scenario
- Update function documentation

pkg/completion/completion.go

@@ -14,7 +14,7 @@ import (
 )
 
 // NeedsUpdate checks if the completion cache needs to be regenerated.
-// Returns true if the file doesn't exist, is older than interval days, or force is true.
+// Returns true if the file doesn't exist, is older than interval days, is empty, or force is true.
 func NeedsUpdate(completionPath string, interval int, force bool) bool {
 	if force {
 		return true
@@ -25,6 +25,11 @@ func NeedsUpdate(completionPath string, interval int, force bool) bool {
 		return true
 	}
 
+	// If the file is empty or invalid, regenerate it
+	if info.Size() == 0 {
+		return true
+	}
+
 	if interval != -1 && time.Since(info.ModTime()).Hours() >= float64(interval*24) {
 		return true
 	}

pkg/completion/completion_test.go

@@ -210,6 +210,18 @@ func TestNeedsUpdate(t *testing.T) {
 			force:          false,
 			expectedResult: false,
 		},
+		{
+			name: "empty file returns true",
+			setupFile: func(t *testing.T, path string) {
+				t.Helper()
+				// Create an empty file
+				err := os.WriteFile(path, []byte(""), 0o600)
+				require.NoError(t, err)
+			},
+			interval:       7,
+			force:          false,
+			expectedResult: true,
+		},
 	}
 
 	for _, tt := range tests {