Swift: fix extraction of empty files

Author: redsun82

swift/extractor/SwiftExtractor.cpp

@@ -134,7 +134,10 @@ static void extractDeclarations(const SwiftExtractorConfiguration& config,
   for (auto decl : topLevelDecls) {
     visitor.extract(decl);
   }
-  if (topLevelDecls.empty()) {
+  // TODO the following will be moved to the dispatcher when we start caching swift file objects
+  // for the moment, topLevelDecls always contains the current module, which does not have a file
+  // associated with it, so we need a special case when there are no top level declarations
+  if (topLevelDecls.size() == 1) {
     // In the case of empty files, the dispatcher is not called, but we still want to 'record' the
     // fact that the file was extracted
     llvm::SmallString<PATH_MAX> name(filename);

swift/ql/test/extractor-tests/generated/File/File.expected

@@ -1,2 +1,3 @@
+| empty.swift:0:0:0:0 | empty.swift | getName: | empty.swift |
 | file://:0:0:0:0 |  | getName: |  |
-| hello.swift:0:0:0:0 | hello.swift | getName: | hello.swift |
+| non_empty.swift:0:0:0:0 | non_empty.swift | getName: | non_empty.swift |

swift/ql/test/extractor-tests/generated/File/hello.swift renamed to swift/ql/test/extractor-tests/generated/File/empty.swift

@@ -0,0 +1 @@
+print("hello")