anchor.diff:              // Ignore warnings about 'const' factories in the patched SDK.
               continue;
             }
  -          errors.add(error);
  +          lines ??= context.computeLineInfo(source);
  +          errors.add(formatErrorMessage(error, source.shortName, lines));
           }
         }
       }
  
positive.code:     context.resolveCompilationUnit(source, element);
      _buildLibraryBody(element, node);
      for (var unit in element.units) {
        for (var error in context.computeErrors(unit.source)) {
          if (error.errorCode is CompileTimeErrorCode ||
              error.errorCode is ParserErrorCode ||
  
negative.code:     });
    }
  
    String formatErrorMessage(
        AnalysisError error, String filename, LineInfo lines) {
      var location = lines.getLocation(error.offset);
      return '[error] ${error.message} ($filename, '
          'line ${location.lineNumber}, '
          'col ${location.columnNumber})';
    }
  
    void ensureLibraryIsLoaded(ast.Library node) {
      if (node.isLoaded) return;
      var source = context.sourceFactory.forUri2(node.importUri);
  