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bug: Windows build fails with C4819+C2220 error when using serious_python after upgrading Flet to 0.86 #6686
Description
Duplicate Check
- I have searched the opened issues and there are no duplicates
Describe the bug
After upgrading Flet to version 0.86, running flet build windows -vv fails.
serious_python_windows_plugin.cpp(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
serious_python_windows_plugin.cpp(1,1): error C2220: the following warning is treated as an error
Code sample
Code
Use a simple counter.py
import flet as ft
def main(page: ft.Page):
page.title = "Flet counter example"
page.vertical_alignment = ft.MainAxisAlignment.CENTER
input = ft.TextField(value="0", text_align=ft.TextAlign.RIGHT, width=100)
def minus_click(e):
input.value = str(int(input.value) - 1)
def plus_click(e):
input.value = str(int(input.value) + 1)
page.add(
ft.Row(
alignment=ft.MainAxisAlignment.CENTER,
controls=[
ft.IconButton(ft.Icons.REMOVE, on_click=minus_click),
input,
ft.IconButton(ft.Icons.ADD, on_click=plus_click),
],
)
)
ft.run(main)To reproduce
- Upgrade flet to 0.86
- Run flet build windows -vv
Expected behavior
No response
Screenshots / Videos
Captures
[Upload media here]
Operating System
Windows
Operating system details
Windows 11 Chinese Simplified
Flet version
0.86
Regression
Yes, it used to work in a previous Flet version (please specify the version in additional details)
Suggestions
- I’m in mainland China, Powershell input: [System.Text.Encoding]::Default.CodePage, output:936, represents GBK；
- On Simplified Chinese Windows, default system code page is 936 (GBK). MSVC cannot parse UTF-8 source without BOM under GBK codepage → triggers C4819.
- Because /WX is active, this encoding warning is escalated to a fatal build error C2220.
Logs
Logs
[ ] C:\Program Files\Microsoft Visual
Studio\18\Community\VC\Tools\MSVC\14.51.36231\bin\HostX64\x64\CL.exe /c
/I"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral"
/I"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\cpp_client_wrapper\incl
ude" /nologo /W4 /WX /diagnostics:column /O2 /Ob2 /D _WINDLL /D _UNICODE /D UNICODE /D WIN32 /D
_WINDOWS /D NDEBUG /D _HAS_EXCEPTIONS=0 /D _SILENCE_EXPERIMENTAL_COROUTINE_DEPRECATION_WARNINGS
/D FLUTTER_PLUGIN_IMPL /D UNICODE /D _UNICODE /D "CMAKE_INTDIR=\"Release\"" /D
url_launcher_windows_plugin_EXPORTS /EHsc /MD /GR /std:c++17
/Fo"url_launcher_windows_plugin.dir\Release\\"
/Fd"url_launcher_windows_plugin.dir\Release\vc145.pdb" /external:W4 /TP /wd4100
/errorReport:queue
"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\.plugin_symlinks\url_laun
cher_windows\windows\url_launcher_windows.cpp"
"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\.plugin_symlinks\url_laun
cher_windows\windows\messages.g.cpp"
"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\.plugin_symlinks\url_laun
cher_windows\windows\system_apis.cpp"
"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\.plugin_symlinks\url_laun
cher_windows\windows\url_launcher_plugin.cpp"
[16:41:36] [ +60 ms] url_launcher_windows.cpp
[16:41:37] [+1778 ms] messages.g.cpp
[16:41:39] [+1292 ms] system_apis.cpp
[ +540 ms] url_launcher_plugin.cpp
[16:41:41] [+1771 ms] 正在生成代码...
[16:41:42] [+1442 ms] Link:
[ ] C:\Program Files\Microsoft Visual
Studio\18\Community\VC\Tools\MSVC\14.51.36231\bin\HostX64\x64\link.exe
/OUT:"D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\url_launcher_windows
\Release\url_launcher_windows_plugin.dll" /INCREMENTAL:NO /NOLOGO
..\..\flutter\Release\flutter_wrapper_plugin.lib shlwapi.lib
"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\flutter_windows.dll.lib"
kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib
comdlg32.lib advapi32.lib /MANIFEST /MANIFESTUAC:"level='asInvoker' uiAccess='false'"
/manifest:embed
/PDB:"D:/PythonProjects/flet-counter/build/flutter/build/windows/x64/plugins/url_launcher_windows
/Release/url_launcher_windows_plugin.pdb" /SUBSYSTEM:CONSOLE /TLBID:1
/IMPLIB:"D:/PythonProjects/flet-counter/build/flutter/build/windows/x64/plugins/url_launcher_wind
ows/Release/url_launcher_windows_plugin.lib" /MACHINE:X64 /machine:x64 /DLL
url_launcher_windows_plugin.dir\Release\url_launcher_windows.obj
[ ] url_launcher_windows_plugin.dir\Release\messages.g.obj
[ ] url_launcher_windows_plugin.dir\Release\system_apis.obj
[ ] url_launcher_windows_plugin.dir\Release\url_launcher_plugin.obj
[ +79 ms] 正在创建库
D:/PythonProjects/flet-counter/build/flutter/build/windows/x64/plugins/url_launcher_windows/Relea
se/url_launcher_windows_plugin.lib 和对象
D:/PythonProjects/flet-counter/build/flutter/build/windows/x64/plugins/url_launcher_windows/Relea
se/url_launcher_windows_plugin.exp
[16:41:43] [ +99 ms] url_launcher_windows_plugin.vcxproj ->
D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\url_launcher_windows\Relea
se\url_launcher_windows_plugin.dll
[ +9 ms] FinalizeBuildStatus:
[ ]
正在删除文件“url_launcher_windows_plugin.dir\Release\url_laun.B79FF416.tlog\unsuccessfulbuild”。
[ ]
正在对“url_launcher_windows_plugin.dir\Release\url_laun.B79FF416.tlog\url_launcher_windows_plugin
.lastbuildstate”执行 Touch 任务。
[ ]
已完成生成项目“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\url_launche
r_windows\url_launcher_windows_plugin.vcxproj”(默认目标)的操作。
[ +33 ms]
项目“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\runner\flet_counter.vcxproj”(
9)正在节点 1
上生成“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\window_manager\wind
ow_manager_plugin.vcxproj”(17) (默认目标)。
[ ] PrepareForBuild:
[ ] 已启用结构化输出。编译器诊断的格式设置将反映错误层次结构。有关详细信息，请参阅
https://aka.ms/cpp/structured-output。
[ ]
正在创建目录“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\window_manage
r\Release\”。
[ ] 正在创建目录“window_manager_plugin.dir\Release\window_m.4493C673.tlog\”。
[ +2 ms] InitializeBuildStatus:
[ ]
正在创建“window_manager_plugin.dir\Release\window_m.4493C673.tlog\unsuccessfulbuild”，因为已指定“
AlwaysCreate”。
[ ]
正在对“window_manager_plugin.dir\Release\window_m.4493C673.tlog\unsuccessfulbuild”执行 Touch
任务。
[ +65 ms] CustomBuild:
[ ] Building Custom Rule
D:/PythonProjects/flet-counter/build/flutter/windows/flutter/ephemeral/.plugin_symlinks/window_ma
nager/windows/CMakeLists.txt
[ +65 ms] ClCompile:
[ ] C:\Program Files\Microsoft Visual
Studio\18\Community\VC\Tools\MSVC\14.51.36231\bin\HostX64\x64\CL.exe /c
/I"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral"
/I"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\cpp_client_wrapper\incl
ude" /nologo /W4 /WX /diagnostics:column /O2 /Ob2 /D _WINDLL /D _UNICODE /D UNICODE /D WIN32 /D
_WINDOWS /D NDEBUG /D _HAS_EXCEPTIONS=0 /D _SILENCE_EXPERIMENTAL_COROUTINE_DEPRECATION_WARNINGS
/D FLUTTER_PLUGIN_IMPL /D _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING /D UNICODE /D
_UNICODE /D "CMAKE_INTDIR=\"Release\"" /D window_manager_plugin_EXPORTS /EHsc /MD /GR /std:c++17
/Fo"window_manager_plugin.dir\Release\\" /Fd"window_manager_plugin.dir\Release\vc145.pdb"
/external:W4 /TP /wd4100 /errorReport:queue
"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\.plugin_symlinks\window_m
anager\windows\window_manager.cpp"
"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\.plugin_symlinks\window_m
anager\windows\window_manager_plugin.cpp"
[ +61 ms] window_manager.cpp
[16:41:45] [+2124 ms] window_manager_plugin.cpp
[16:41:47] [+2393 ms] 正在生成代码...
[16:41:49] [+1418 ms] Link:
[ ] C:\Program Files\Microsoft Visual
Studio\18\Community\VC\Tools\MSVC\14.51.36231\bin\HostX64\x64\link.exe
/OUT:"D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\window_manager\Relea
se\window_manager_plugin.dll" /INCREMENTAL:NO /NOLOGO
..\..\flutter\Release\flutter_wrapper_plugin.lib
"D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\flutter_windows.dll.lib"
kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib
comdlg32.lib advapi32.lib /MANIFEST /MANIFESTUAC:"level='asInvoker' uiAccess='false'"
/manifest:embed
/PDB:"D:/PythonProjects/flet-counter/build/flutter/build/windows/x64/plugins/window_manager/Relea
se/window_manager_plugin.pdb" /SUBSYSTEM:CONSOLE /TLBID:1
/IMPLIB:"D:/PythonProjects/flet-counter/build/flutter/build/windows/x64/plugins/window_manager/Re
lease/window_manager_plugin.lib" /MACHINE:X64 /machine:x64 /DLL
window_manager_plugin.dir\Release\window_manager.obj
[ ] window_manager_plugin.dir\Release\window_manager_plugin.obj
[ +84 ms] 正在创建库
D:/PythonProjects/flet-counter/build/flutter/build/windows/x64/plugins/window_manager/Release/win
dow_manager_plugin.lib 和对象
D:/PythonProjects/flet-counter/build/flutter/build/windows/x64/plugins/window_manager/Release/win
dow_manager_plugin.exp
[ +99 ms] window_manager_plugin.vcxproj ->
D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\window_manager\Release\win
dow_manager_plugin.dll
[ +8 ms] FinalizeBuildStatus:
[ ]
正在删除文件“window_manager_plugin.dir\Release\window_m.4493C673.tlog\unsuccessfulbuild”。
[ ]
正在对“window_manager_plugin.dir\Release\window_m.4493C673.tlog\window_manager_plugin.lastbuildst
ate”执行 Touch 任务。
[ ]
已完成生成项目“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\window_mana
ger\window_manager_plugin.vcxproj”(默认目标)的操作。
[ +1 ms]
已完成生成项目“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\runner\flet_counter
.vcxproj”(默认目标)的操作 - 失败。
[ +1 ms]
已完成生成项目“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\ALL_BUILD.vcxproj”(
默认目标)的操作 - 失败。
[ ]
已完成生成项目“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\INSTALL.vcxproj”(默
认目标)的操作 - 失败。
[ +12 ms] 生成失败。
[ ]
“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\INSTALL.vcxproj”(默认目标) (1) ->
[ ]
“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\ALL_BUILD.vcxproj”(默认目标) (3)
->
[ ]
“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\runner\flet_counter.vcxproj”(默认
目标) (9) ->
[ ]
“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\serious_python_windows\se
rious_python_windows_plugin.vcxproj”(默认目标) (14) ->
[ ] (ClCompile 目标) ->
[ ]
D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\.plugin_symlinks\serious_p
ython_windows\windows\serious_python_windows_plugin.cpp(1,1): warning C4819:
该文件包含不能在当前代码页(936)中表示的字符。请将该文件保存为 Unicode 格式以防止数据丢失
[D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\serious_python_windows\se
rious_python_windows_plugin.vcxproj]
[ ]
“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\INSTALL.vcxproj”(默认目标) (1) ->
[ ]
“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\ALL_BUILD.vcxproj”(默认目标) (3)
->
[ ]
“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\runner\flet_counter.vcxproj”(默认
目标) (9) ->
[ ]
“D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\serious_python_windows\se
rious_python_windows_plugin.vcxproj”(默认目标) (14) ->
[ ] (ClCompile 目标) ->
[ ]
D:\PythonProjects\flet-counter\build\flutter\windows\flutter\ephemeral\.plugin_symlinks\serious_p
ython_windows\windows\serious_python_windows_plugin.cpp(1,1): error C2220: 以下警告被视为错误
[D:\PythonProjects\flet-counter\build\flutter\build\windows\x64\plugins\serious_python_windows\se
rious_python_windows_plugin.vcxproj]
[ ] 1 个警告
[ ] 1 个错误
[ ] 已用时间 00:02:18.57
[ +29 ms] Building Windows application... (completed in 144.2s)
[ ] "flutter windows" took 148,533ms.
[ +67 ms] Build process failed.
[ ]
#0 throwToolExit (package:flutter_tools/src/base/common.dart:34:3)
#1 _runBuild (package:flutter_tools/src/windows/build_windows.dart:262:5)
<asynchronous suspension>
#2 buildWindows (package:flutter_tools/src/windows/build_windows.dart:118:5)
<asynchronous suspension>
#3 BuildWindowsCommand.runCommand
(package:flutter_tools/src/commands/build_windows.dart:72:5)
<asynchronous suspension>
#4 FlutterCommand.run.<anonymous closure>
(package:flutter_tools/src/runner/flutter_command.dart:1630:27)
<asynchronous suspension>
#5 AppContext.run.<anonymous closure>
(package:flutter_tools/src/base/context.dart:154:19)
<asynchronous suspension>
#6 CommandRunner.runCommand (package:args/command_runner.dart:212:13)
<asynchronous suspension>
#7 FlutterCommandRunner.runCommand.<anonymous closure>
(package:flutter_tools/src/runner/flutter_command_runner.dart:496:9)
<asynchronous suspension>
#8 AppContext.run.<anonymous closure>
(package:flutter_tools/src/base/context.dart:154:19)
<asynchronous suspension>
#9 FlutterCommandRunner.runCommand
(package:flutter_tools/src/runner/flutter_command_runner.dart:431:5)
<asynchronous suspension>
#10 FlutterCommandRunner.run.<anonymous closure>
(package:flutter_tools/src/runner/flutter_command_runner.dart:307:33)
<asynchronous suspension>
#11 run.<anonymous closure>.<anonymous closure>
(package:flutter_tools/runner.dart:104:11)
<asynchronous suspension>
#12 AppContext.run.<anonymous closure>
(package:flutter_tools/src/base/context.dart:154:19)
<asynchronous suspension>
#13 main (package:flutter_tools/executable.dart:103:3)
<asynchronous suspension>
[ ] Running 1 shutdown hook
[ +11 ms] Shutdown hooks complete
[ +23 ms] exiting with code 1Additional details
No response
Reacted by MRDXHMAGIC
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FeodorFitsner commentedon Jul 15, 2026
Working on a fix.
Muddassir-Farooq-official commentedon Jul 15, 2026
There is also an issue with --port and -d and -r arguments when run with flet run main.py --web
Fix Windows build failure on non-UTF-8 locales (C4819/C2220) (#234)
KangZhaoKui commentedon Jul 16, 2026
Thank you @FeodorFitsner ! I've tested it, and serious_python_windows_plugin.cpp is fixed, but I found another file with the same issue:
connectivity_plus_plugin.cpp，After making these changes, it won't fail again! Thank you again for your efforts.
MRDXHMAGIC commentedon Jul 16, 2026
Open "Beta 版：使用 Unicode UTF-8 提供全球语言支持" can fix MSVC C4819 error.
Compile Windows plugins with /utf-8 in build template
FeodorFitsner commentedon Jul 16, 2026
The fix is coming guys: #6687
Fix Windows build on non-UTF-8 locales (/utf-8 template + serious_pyt…
FeodorFitsner commentedon Jul 17, 2026
It's been fixed in 0.86.1.