Fix for crash when part directive uri is has null value.

R=brianwilkerson@google.com, paulberry@google.com
BUG=

Review-Url: https://codereview.chromium.org/2628303002 .

pkg/analyzer/lib/src/summary/public_namespace_computer.dart

@@ -178,7 +178,7 @@ class _PublicNamespaceVisitor extends RecursiveAstVisitor {
 
   @override
   visitPartDirective(PartDirective node) {
-    parts.add(node.uri.stringValue);
+    parts.add(node.uri.stringValue ?? '');
   }
 
   @override

pkg/analyzer/test/generated/compile_time_error_code_driver_test.dart

@@ -65,10 +65,4 @@ class CompileTimeErrorCodeTest_Driver extends CompileTimeErrorCodeTest {
   test_uriDoesNotExist_import_appears_after_deleting_target() {
     return super.test_uriDoesNotExist_import_appears_after_deleting_target();
   }
-
-  @failingTest
-  @override
-  test_uriWithInterpolation_nonConstant() {
-    return super.test_uriWithInterpolation_nonConstant();
-  }
 }

pkg/analyzer/test/src/summary/resynthesize_common.dart

@@ -4345,6 +4345,15 @@ void named({x: 1}) {}
     checkLibrary('library my.lib; part "foo/";');
   }
 
+  test_parts_invalidUri_nullStringValue() {
+    allowMissingFiles = true;
+    addSource('/foo/bar.dart', 'part of my.lib;');
+    checkLibrary(r'''
+library my.lib;
+part "${foo}/bar.dart";
+''');
+  }
+
   test_propagated_type_refers_to_closure() {
     checkLibrary('''
 void f() {

pkg/analyzer/test/src/summary/summary_common.dart

@@ -6471,6 +6471,17 @@ class B extends A {}
     expect(unlinkedExports[0].configurations, isEmpty);
   }
 
+  test_export_uri_nullStringValue() {
+    String libraryText = r'''
+export "${'a'}.dart";
+''';
+    serializeLibraryText(libraryText);
+    var unlinkedExports = unlinkedUnits[0].publicNamespace.exports;
+    expect(unlinkedExports, hasLength(1));
+    expect(unlinkedExports[0].uri, '');
+    expect(unlinkedExports[0].configurations, isEmpty);
+  }
+
   test_export_variable() {
     addNamedSource('/a.dart', 'var v;');
     serializeLibraryText('export "a.dart";');
@@ -8346,6 +8357,16 @@ class D extends p.C {} // Prevent "unused import" warning
     expect(unlinkedUnits[0].imports[0].uri, 'dart:async');
   }
 
+  test_import_uri_nullStringValue() {
+    String libraryText = r'''
+import "${'a'}.dart";
+''';
+    serializeLibraryText(libraryText);
+    // Second import is the implicit import of dart:core
+    expect(unlinkedUnits[0].imports, hasLength(2));
+    expect(unlinkedUnits[0].imports[0].uri, '');
+  }
+
   test_inferred_function_type_parameter_type_with_unrelated_type_param() {
     if (!strongMode || skipFullyLinkedData) {
       return;
@@ -9475,6 +9496,20 @@ f(x) => 42;
     expect(unlinkedUnits[0].parts[0].uriEnd, text.indexOf('; // <-part'));
   }
 
+  test_part_declaration_invalidUri_nullStringValue() {
+    addNamedSource('/a.dart', 'part of my.lib;');
+    String text = r'''
+library my.lib;
+part "${'a'}.dart"; // <-part
+''';
+    serializeLibraryText(text);
+    expect(unlinkedUnits[0].publicNamespace.parts, hasLength(1));
+    expect(unlinkedUnits[0].publicNamespace.parts[0], '');
+    expect(unlinkedUnits[0].parts, hasLength(1));
+    expect(unlinkedUnits[0].parts[0].uriOffset, text.indexOf(r'"${'));
+    expect(unlinkedUnits[0].parts[0].uriEnd, text.indexOf('; // <-part'));
+  }
+
   test_part_isPartOf() {
     addNamedSource('/a.dart', 'part of foo; class C {}');
     serializeLibraryText('library foo; part "a.dart";');