Copy PossiblyContainDynamicImport from old source file to new one

Author: Kanchalai Tanglertsampan

src/compiler/parser.ts

@@ -481,7 +481,11 @@ namespace ts {
     // becoming detached from any SourceFile).  It is recommended that this SourceFile not
     // be used once 'update' is called on it.
     export function updateSourceFile(sourceFile: SourceFile, newText: string, textChangeRange: TextChangeRange, aggressiveChecks?: boolean): SourceFile {
-        return IncrementalParser.updateSourceFile(sourceFile, newText, textChangeRange, aggressiveChecks);
+        const newSourceFile = IncrementalParser.updateSourceFile(sourceFile, newText, textChangeRange, aggressiveChecks);
+        // Because new source file node is created, it may not have the flag PossiblyContainDynamicImport. This is the case if there is no new edit to add dynamic import.
+        // We will manually port the flag to the new source file.
+        newSourceFile.flags |= (sourceFile.flags & NodeFlags.PossiblyContainDynamicImport);
+        return newSourceFile;
     }
 
     /* @internal */