anchor.diff:  
       Archive archive = new Archive();
   
  -    int result = await toolchain.compiler.compile(mainPath: mainPath, snapshotPath: snapshotPath);
  -    if (result != 0)
  -      return result;
  -
  -    archive.addFile(_createSnapshotFile(snapshotPath));
  +    if (!precompiledSnapshot) {
  +      // In a precompiled snapshot, the instruction buffer contains script
  +      // content equivalents
  +      int result = await toolchain.compiler.compile(mainPath: mainPath, snapshotPath: snapshotPath);
  +      if (result != 0)
  +        return result;
  +
  +      archive.addFile(_createSnapshotFile(snapshotPath));
  +    }
   
       for (_Asset asset in assets)
         archive.addFile(_createFile(asset.key, asset.base));
  
positive.code:     String manifestPath,
      String outputPath: _kDefaultOutputPath,
      String snapshotPath: _kDefaultSnapshotPath,
      String privateKeyPath: _kDefaultPrivateKeyPath
    }) async {
      Map manifestDescriptor = _loadManifest(manifestPath);
  
  
negative.code:       manifestPath: argResults['manifest'],
        outputPath: argResults['output-file'],
        snapshotPath: argResults['snapshot'],
        privateKeyPath: argResults['private-key'],
        precompiledSnapshot: argResults['precompiled']
      );
    }
  
  