If there is a changed file, hasFilesToAnalyze is true.

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index d900475ad09919c4d1e0f2152959f00b4ea1f5d9..5525c3d00ed5b86fae52526ef25b19c9a09c4e42 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -274,7 +274,8 @@ class AnalysisDriver {
    * Return `true` if the driver has a file to analyze.
    */
   bool get hasFilesToAnalyze {
-    return _requestedFiles.isNotEmpty ||
+    return _changedFiles.isNotEmpty ||
+        _requestedFiles.isNotEmpty ||
         _requestedParts.isNotEmpty ||
         _filesToAnalyze.isNotEmpty ||
         _partsToAnalyze.isNotEmpty;