anchor.diff:  
       REM Makes changes to PUB_ENVIRONMENT only visible to commands within SETLOCAL/ENDLOCAL
       SETLOCAL
  -    IF "%TRAVIS%" == "true" GOTO on_bot
  -    IF "%BOT%" == "true" GOTO on_bot
  -    IF "%CONTINUOUS_INTEGRATION%" == "true" GOTO on_bot
  -    IF "%CHROME_HEADLESS%" == "1" GOTO on_bot
  -    IF "%APPVEYOR%" == "true" GOTO on_bot
  -    IF "%CI%" == "true" GOTO on_bot
  -    GOTO not_on_bot
  -    :on_bot
  -      SET PUB_ENVIRONMENT=%PUB_ENVIRONMENT%:flutter_bot
  -    :not_on_bot
  -    SET PUB_ENVIRONMENT=%PUB_ENVIRONMENT%:flutter_install
  -    CALL "%pub%" upgrade --verbosity=error --no-packages-dir
  +      IF "%TRAVIS%" == "true" GOTO on_bot
  +      IF "%BOT%" == "true" GOTO on_bot
  +      IF "%CONTINUOUS_INTEGRATION%" == "true" GOTO on_bot
  +      IF "%CHROME_HEADLESS%" == "1" GOTO on_bot
  +      IF "%APPVEYOR%" == "true" GOTO on_bot
  +      IF "%CI%" == "true" GOTO on_bot
  +      GOTO not_on_bot
  +      :on_bot
  +        SET PUB_ENVIRONMENT=%PUB_ENVIRONMENT%:flutter_bot
  +      :not_on_bot
  +      SET PUB_ENVIRONMENT=%PUB_ENVIRONMENT%:flutter_install
  +      :retry_pub_upgrade
  +      CALL "%pub%" upgrade --verbosity=error --no-packages-dir
  +      IF "%ERRORLEVEL%" NEQ "0" (
  +        ECHO Error: Unable to 'pub upgrade' flutter tool. Retrying...
  +        timeout /t 5 /nobreak
  +        GOTO :retry_pub_upgrade
  +      )
       ENDLOCAL
   
       POPD
  +
  +    :retry_dart_snapshot
       CALL "%dart%" --snapshot="%snapshot_path%" --packages="%flutter_tools_dir%\.packages" "%script_path%"
  +    IF "%ERRORLEVEL%" NEQ "0" (
  +      ECHO Error: Unable to create dart snapshot for flutter tool. Retrying...
  +      timeout /t 5 /nobreak
  +      GOTO :retry_dart_snapshot
  +    )
       >"%stamp_path%" ECHO %revision%
   
     REM Exit Subroutine
  
positive.code:   :do_sdk_update_and_snapshot
      ECHO Checking Dart SDK version...
      CALL PowerShell.exe -ExecutionPolicy Bypass -Command "& '%FLUTTER_ROOT%/bin/internal/update_dart_sdk.ps1'"
      SET exit_code=%ERRORLEVEL%
      IF %exit_code% NEQ 0 (
        ECHO Error: Unable to update Dart SDK. Retrying... Press Ctrl+C to abort.
        GOTO :do_sdk_update_and_snapshot
      )
  
  
negative.code: SET exit_code=%ERRORLEVEL%
  
  REM The VM exits with code 253 if the snapshot version is out-of-date.
  IF "%exit_code%" EQU "253" (
    CALL "%dart%" --snapshot="%snapshot_path%" --packages="%flutter_tools_dir%\.packages" "%script_path%"
    SET exit_code=%ERRORLEVEL%
    IF "%exit_code%" EQU "253" (
      ECHO Error: Unable to create dart snapshot for flutter tool.
      EXIT /B %exit_code%
    )
    CALL "%dart%" %FLUTTER_TOOL_ARGS% "%snapshot_path%" %*
    SET exit_code=%ERRORLEVEL%
  )
  