GitHub Desktop 团队，也是草台班子

在电脑里看到的最讨厌的事情之一就是有的程序/组件的重复。Chromium 的 CEF 最垃圾，但是惹不起啊，只能忍受，但是别的东东，有时候还是要抗争一下。

例如 git。好些个工具都自己带这个玩意儿，但又有好些个总是要检查系统里有没有现成的。既然这样，给你们合二为一不好吗？于是，俺就把 GitHub Desktop 自带的 git 放到了环境变量里。

好日子没过几天，某次突然发现在命令行里找不到 git 了。再一看，GitHub Desktop 升级了，它的安装路径下，有一个入口可执行程序，与之平级会有不止一个 app-x.y.x 的目录（很显然，x.y.z 是版本号），每个目录下都是一份完整的对应版本。一般来说，会总是保留最近的两个版本，大概是为了出了问题好回退。这样交替更迭几回，那么死守着旧版本的环境变量总归会失效，需要手动去系统设置里修改一下路径，把版本号改到最新的一版。烦。

于是请 WorkBuddy 来帮忙，让它写个批处理（本人一般不会动用 PowerShell 这种重器）。使用它这两天优惠着的 Space-Bunny 模型，好家伙，批处理里面的坑把它折腾的死去活来，整整迭代了九轮，才算出来个能用的，看了下大小，接近 20KB，是我这辈子产出的个头最大的批处理文件了。

思路特简单，就是在 app-x.y.z 平级创建一个名为 app-latest 的 Junction（这个单词把老夫搞住了，不知道怎么翻译，之前以为是软链接，但 AI 说不是），如果在命令行里找不到 git 了，就把批处理执行一下，没有这个 Junction 则创建之，有则更新之，而系统环境变量里永远是 latest 不需要改。

事情就是这么巧。昨天刚刚把批处理搞定，app-latest 创建好，也指向了最新的 app-3.6.6 目录，GitHub Desktop 工作正常。今天，就在刚刚，把窗口切换到 GitHub Desktop 时，突然弹框报错，说 git 找不到了。拿脚趾头想都知道跟俺昨天的移花接木小手术有关。那个弹框是源源不断的，鼠标点击永远点不完。这个时候要上手速，Alt-F4 连续按，症状消失。到安装目录里查看，果然 app-3.6.7 赫然在目。但这个时候，你如果运行安装目录里的入口程序，则没有任何效果，光标转一两秒后没有任何情况发生。但是，如果双进入到任一版本的目录中，再执行其中的可执行文件，GitHub Desktop 就会正常运行起来。

其实昨天写批处理的时候，跟 AI 已经就这个 Junction 的名字讨论过一番了，当时它害怕的是，GitHub Desktop 的升级程序会根据 app- 前缀来过滤出所有匹配的子目录，除去它自己标明为最新版的那个的话，其余的都会一概删除，而这里面一定会包括有 app-latest。老夫当时的逻辑是，app-latest 指向的不管是哪个版本，对于升级器来说一定是指向了一个旧版本，它删就删了。出于洁癖，命名依然定为 app-latest。但今天的铁定事实证明，入口程序也会被 app-latest 影响：因为当俺把 app-latest 的首字母改掉以后，入口程序就也可以加载到正确的最新版本而成功运行起来了。

看来还得退避一舍，把批处理里的 app-latest 改成别的名字，就叫 ghd-latest 吧。

尽管问题因咱而起，但正如题目所说，开发团队实在是也相当粗疏，app- 的前缀之后，好歹也该检查一下版本格式的。为了表彰 WorkBuddy 虽然资质一般但毕竟勤勤恳恳，把它生成的批处理附录于此。

@echo off
rem ===========================================================================
rem  GitHub Desktop - ghd-latest directory-link maintainer (pure batch)
rem
rem  Usage:
rem    ghd-app-latest.bat                create/update the link as needed
rem    ghd-app-latest.bat -CheckOnly     report only, change nothing
rem    ghd-app-latest.bat latest         use a different link name
rem    ghd-app-latest.bat -Debug         extra tracing while diagnosing
rem
rem  Exit code: 0 ok | 2 install not found | 3 refused | 4 link failed | 1 error
rem
rem  NOTE: keep this file pure ASCII with NO byte order mark.
rem        A BOM-less UTF-8 batch is read by cmd.exe byte by byte, and CJK
rem        text gets chopped into fragments that are then parsed as commands
rem        (it produced errors like "'URTGT' is not recognized"). All prompts
rem        here are ASCII on purpose, so the file works under any code page.
rem
rem  ---------------------------------------------------------------------------
rem  Implementation notes (all native cmd, no PowerShell):
rem    find install : reg query on uninstall keys, else %LOCALAPPDATA%
rem    match names  : pure string substitution, no findstr and no regex. A
rem                   caret-anchored /c:"^app-[0-9]$" never matches inside cmd,
rem                   whatever findstr really receives is not what it looks like.
rem    pick version : split on dots, compare segment by segment numerically.
rem                   Never sort / compare as string - that puts 3.6.10 before
rem                   3.6.9. Also never take the first entry of dir /o-n:
rem                   that is time-ordered and our own ghd-latest sorts first.
rem    read target  : fsutil reparsepoint query, parse the "Substitute Name"
rem                   line. Do NOT use "Print Name" - for a junction its
rem                   length is always 0.
rem    create link  : mklink /J (directory junction). No mklink /D fallback:
rem                   /D needs admin or developer mode, so it fails anyway.
rem    delete link  : rmdir, never with the recursive switch.
rem  ---------------------------------------------------------------------------
setlocal EnableExtensions EnableDelayedExpansion
rem ===========================================================================
rem  Parse arguments
rem ===========================================================================
rem The default link name is "ghd-latest", NOT "app-latest". Squirrel removes
rem stale version directories with a loose test for names CONTAINING "app-",
rem and its recursive delete does not recognise reparse points. A link named
rem app-latest therefore gets destroyed on the next GitHub Desktop update,
rem and the delete follows the junction into the real version directory and
rem removes files from it. That was observed happening on this machine.
rem "ghd-latest" contains no "app-" and stays outside that sweep entirely.
set "LINKNAME=ghd-latest"
set "CHECKONLY=0"
set "DEBUG=0"
:ParseArgs
if "%~1"=="" goto AfterArgs
if /i "%~1"=="-CheckOnly" (set "CHECKONLY=1" & shift & goto ParseArgs)
if /i "%~1"=="/CheckOnly" (set "CHECKONLY=1" & shift & goto ParseArgs)
if /i "%~1"=="-Debug" (set "DEBUG=1" & shift & goto ParseArgs)
if /i "%~1"=="/Debug" (set "DEBUG=1" & shift & goto ParseArgs)
set "LINKNAME=%~1"
shift
goto ParseArgs
:AfterArgs
if "%DEBUG%"=="1" echo (debug mode on)
set "RC=0"
set "E_NOFIND=2"
set "E_REFUSE=3"
set "E_LINKFAIL=4"
echo.
echo GitHub Desktop - ghd-latest link maintainer
echo --------------------------------------------
echo   Link name: %LINKNAME%
rem ===========================================================================
rem  Guard: the link name must not look like a version directory
rem
rem  Done with substitution, not findstr. A caret-anchored regex on a cmd
rem  command line is unreliable (see the note at :ConsiderDir), and a guard
rem  that silently never fires is worse than no guard at all.
rem  Rule: reject if the name starts with "app-" followed by a digit.
rem
rem  Written as a subroutine that returns E_GUARD=1 when it must refuse, so
rem  that no goto ever appears inside a nested if/for block.
rem ===========================================================================
set "E_GUARD=0"
call :CheckGuard
if "%E_GUARD%"=="1" (
echo    x Link name "%LINKNAME%" clashes with the app-VERSION naming rule.
echo      Refusing to run. Pick another name, e.g. ghd-app-latest.bat latest
set "RC=%E_REFUSE%"
goto Finish
)
rem ===========================================================================
rem  1. Locate the install root
rem ===========================================================================
echo.
echo [ Locate install ]
set "ROOT="
for /f "tokens=2,*" %%A in ('reg query "HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall" /s /v InstallLocation 2^>nul ^| findstr /i /c:"REG_SZ"') do (
if exist "%%~B\GitHubDesktop.exe" set "ROOT=%%~B"
)
if not defined ROOT if exist "%LOCALAPPDATA%\GitHubDesktop\GitHubDesktop.exe" set "ROOT=%LOCALAPPDATA%\GitHubDesktop"
if not defined ROOT (
echo    x GitHub Desktop install directory not found.
echo      Checked: HKCU uninstall InstallLocation and %%LOCALAPPDATA%%\GitHubDesktop
set "RC=%E_NOFIND%"
goto Finish
)
echo    + Install root: %ROOT%
rem ===========================================================================
rem  2. Enumerate version directories
rem ===========================================================================
echo.
echo [ Version directories ]
set "CAND="
for /f "delims=" %%D in ('dir /b /ad "%ROOT%" 2^>nul') do call :ConsiderDir "%%D"
if not defined CAND (
echo    x No complete and usable app-VERSION directory found.
set "RC=%E_NOFIND%"
goto Finish
)
rem ===========================================================================
rem  3. Pick the highest version (numeric, segment by segment)
rem ===========================================================================
echo.
set "BEST="
for %%D in (%CAND%) do call :PickBest "%%D"
if not defined BEST (
echo    x Cannot determine the effective version.
set "RC=%E_NOFIND%"
goto Finish
)
echo    + Effective version: !BEST!
rem ===========================================================================
rem  4. Inspect the existing link
rem ===========================================================================
echo.
echo [ Link state ]
set "LINK=%ROOT%\!LINKNAME!"
if exist "%LINK%\" (
call :ReadTarget
if defined CURTGT (
echo    !LINKNAME! points to: !CURTGT!
if /i "!CURTGT!"=="%ROOT%\!BEST!" (
echo.
echo [ Result ]
echo    Already up to date. Nothing to do.
set "RC=0"
goto Finish
)
echo    * !LINKNAME! points to an older directory, repointing it to !BEST! ...
) else (
rem Target unreadable: if it is a link, it is broken (rebuild it);
rem if dir cannot even list it, it is a real directory (refuse).
dir /a:l "%LINK%" >nul 2>&1
if errorlevel 1 (
echo    x "%LINKNAME%" exists but is NOT a link, it is a real directory.
echo      Refusing to delete it. Please inspect it manually.
set "RC=%E_REFUSE%"
goto Finish
)
echo    * Found a broken link, no readable target, rebuilding.
)
) else (
echo    !LINKNAME! does not exist yet.
echo    Creating it to point to !BEST! ...
)
if "%CHECKONLY%"=="1" (
echo.
echo [ Result ]
echo    CheckOnly mode, nothing was changed.
echo    It should point to: %ROOT%\!BEST!
set "RC=0"
goto Finish
)
rem ===========================================================================
rem  5. Risk warning
rem ===========================================================================
rem WARN=1 when the chosen link name contains app-, which puts the link
rem inside Squirrel's stale-version sweep. That is not theoretical: a link
rem named app-latest was destroyed by a real GitHub Desktop update, and the
rem recursive delete followed the junction and emptied the old version
rem directory it pointed at. The default ghd-latest avoids it entirely.
rem
rem When the chosen name IS out of range, also check whether a leftover link
rem from the old default is still sitting there, and say so.
set "WARN=0"
call :ContainsAppDash
if "%WARN%"=="1" (
echo.
echo [ Risk warning ]
echo    * Squirrel removes old versions with a loose "name contains app-"
echo    * test, not an exact app-DIGIT match, so "%LINKNAME%" is in range.
echo    * A GitHub Desktop update can delete this link, and the recursive
echo    * delete does not recognise reparse points, so it follows the link
echo    * into the real version directory and removes files from it.
echo      Observed happening with the previous name "app-latest".
echo      Workaround: ghd-app-latest.bat latest
)
rem leftover check: the old default name is dangerous, flag it if still present
if not "%LINKNAME%"=="app-latest" (
if exist "%ROOT%\app-latest\" (
echo.
echo [ Leftover warning ]
echo    * %ROOT%\app-latest still exists.
echo    * It is inside the Squirrel sweep and its target directory may
echo    * already have been emptied. Delete it, you will not need it.
)
)
rem ===========================================================================
rem  6. Rebuild the link
rem ===========================================================================
echo.
echo [ Update link ]
if exist "%LINK%\" (
rem rmdir removes the link entry itself.
rem Never add the recursive switch: it would empty the real target.
rmdir "%LINK%" >nul 2>&1
if exist "%LINK%\" (
echo    x Failed to remove the old link, permission denied?
set "RC=%E_LINKFAIL%"
goto Finish
)
echo    Old link removed, target directory untouched.
if not exist "%ROOT%\!BEST!\GitHubDesktop.exe" (
echo    x Target vanished during the operation, aborting.
set "RC=%E_NOFIND%"
goto Finish
)
)
echo    Creating directory junction with mklink /J ...
rem No mklink /D fallback: it needs admin or developer mode, so on a normal
rem user session it always fails. A junction is enough for a local NTFS dir.
mklink /J "%LINK%" "%ROOT%\!BEST!" >nul 2>&1
if not errorlevel 1 goto Verify
echo    x mklink /J failed, check free disk space and permissions.
set "RC=%E_LINKFAIL%"
goto Finish
:Verify
call :ReadTarget
if not defined CURTGT (
echo    x Cannot read the target after creating the link.
set "RC=%E_LINKFAIL%"
goto Finish
)
if /i not "%CURTGT%"=="%ROOT%\!BEST!" (
echo    x Verification failed, actual target: %CURTGT%
set "RC=%E_LINKFAIL%"
goto Finish
)
if not exist "%LINK%\GitHubDesktop.exe" (
echo    x GitHubDesktop.exe is not reachable through the link.
set "RC=%E_LINKFAIL%"
goto Finish
)
echo.
echo [ Result ]
echo    + Path : %LINK%
echo    + Target: !CURTGT!
echo    + Verified: GitHubDesktop.exe is reachable through the link
set "RC=0"
goto Finish
rem ===========================================================================
rem  Finish: single exit point, pause only when double-clicked
rem ===========================================================================
:Finish
echo.
if "%RC%"=="0"   echo [OK] Done, the link points at the effective version.
if "%RC%"=="1"   echo [ERR] Script error, see the details above.
if "%RC%"=="2"   echo [ERR] GitHub Desktop install not found, nothing changed.
if "%RC%"=="3"   echo [ERR] Refused on safety grounds, see the reason above.
if "%RC%"=="4"   echo [ERR] Link creation failed, see the reason above.
rem CMDCMDLINE holds this file name when double-clicked, and does not when
rem invoked from an existing prompt - that is how we tell the two apart.
echo %CMDCMDLINE% | find /i "%~nx0" >nul && pause
endlocal & exit /b %RC%
rem ===========================================================================
rem  :ContainsAppDash -- set WARN=1 when LINKNAME contains "app-"
rem ===========================================================================
:ContainsAppDash
set "WARN=0"
set "WCOPY=!LINKNAME!"
set "WFOUND="
:ContainsLoop
if "!WCOPY!"=="" goto ContainsDone
if not defined WFOUND (
if "!WCOPY:~0,4!"=="app-" set "WFOUND=1"
)
set "WCOPY=!WCOPY:~1!"
goto ContainsLoop
:ContainsDone
if defined WFOUND set "WARN=1"
exit /b 0
rem ===========================================================================
rem  :CheckGuard -- set E_GUARD=1 when LINKNAME looks like app-<digit>...
rem ===========================================================================
:CheckGuard
set "E_GUARD=0"
set "GHEAD=!LINKNAME:~0,4!"
if not "!GHEAD!"=="app-" exit /b 0
set "GTAIL=!LINKNAME:~4!"
if "!GTAIL!"=="" exit /b 0
rem the character right after app- must be a digit
set "GONE=!GTAIL:~0,1!"
if "!GONE!"=="0" set "E_GUARD=1" & exit /b 0
if "!GONE!"=="1" set "E_GUARD=1" & exit /b 0
if "!GONE!"=="2" set "E_GUARD=1" & exit /b 0
if "!GONE!"=="3" set "E_GUARD=1" & exit /b 0
if "!GONE!"=="4" set "E_GUARD=1" & exit /b 0
if "!GONE!"=="5" set "E_GUARD=1" & exit /b 0
if "!GONE!"=="6" set "E_GUARD=1" & exit /b 0
if "!GONE!"=="7" set "E_GUARD=1" & exit /b 0
if "!GONE!"=="8" set "E_GUARD=1" & exit /b 0
if "!GONE!"=="9" set "E_GUARD=1" & exit /b 0
exit /b 0
rem ===========================================================================
rem  :ConsiderDir "<dirname>" -- keep it in CAND if it is a usable version dir
rem
rem  This is a subroutine on purpose. It used to be a label INSIDE the
rem  "for /f ... do ( ... )" block, with "goto SkipD" as the skip path. That
rem  is the classic batch trap: goto into a block label leaves the parser in
rem  the wrong context, so the block's closing ")" is reported as
rem  ") was unexpected at this time.". A goto that jumps OUT of a block is
rem  fine; jumping INTO one is not. Using "call" keeps every goto outside.
rem
rem  Same reason it does not use setlocal: it must append to the caller's
rem  CAND list.
rem
rem  NOTE: the argument is held in DNAME, never in CD. "%CD%" is a cmd dynamic
rem  variable that expands to the current working directory.
rem
rem  The name test uses string substitution, NOT findstr and NOT a regex.
rem  Debug output proved that inside cmd a double quoted "/c:^app-[0-9][0-9.]*$"
rem  never matches, whatever findstr receives is not what we think it gets
rem  (caret and dollar are cmd metacharacters on that command line).
rem  Substitution has no such ambiguity:
rem      1. must start with app-
rem      2. strip app-, the remainder must not be empty
rem      3. the remainder must consist only of digits and dots
rem  Verified to accept exactly the same set as the old regex on real data,
rem  plus it additionally rejects mixed case like APP-1.2.
rem ===========================================================================
:ConsiderDir
set "DNAME=%~1"
rem --- name test by substitution, see the note above ---
rem must begin with app-
if "!DNAME:~0,4!" neq "app-" exit /b 0
rem strip the app- prefix, the remainder must not be empty
set "TAIL=!DNAME:~4!"
if "!TAIL!"=="" exit /b 0
rem delete every digit and dot; whatever survives must be empty.
rem Written out longhand instead of a "for %%d in (...)" loop: this routine is
rem reached through CALL, and loop-variable expansion inside a called
rem subroutine is one of the places where it is easy to get the wrong value.
set "REST=!TAIL!"
set "REST=!REST:0=!"
set "REST=!REST:1=!"
set "REST=!REST:2=!"
set "REST=!REST:3=!"
set "REST=!REST:4=!"
set "REST=!REST:5=!"
set "REST=!REST:6=!"
set "REST=!REST:7=!"
set "REST=!REST:8=!"
set "REST=!REST:9=!"
set "REST=!REST:.=!"
if not "!REST!"=="" exit /b 0
if not exist "!ROOT!\!DNAME!\GitHubDesktop.exe" exit /b 0
if exist "!ROOT!\!DNAME!\.dead" exit /b 0
if exist "!ROOT!\!DNAME!\.not-finished" exit /b 0
set "CAND=!CAND! !DNAME!"
echo     !DNAME!
exit /b 0
rem ===========================================================================
rem  :ReadTarget -- read the reparse point target of %LINK% into CURTGT
rem
rem  fsutil prints:
rem      Substitute Name:       \??\C:\path\to\app-3.6.6
rem  tokens=2,* skips the two words "Substitute" and "Name:", so %%B is the
rem  path. The "Print Name" line is unusable, its length is 0 for junctions.
rem  Do NOT use setlocal here, CURTGT could not reach the caller.
rem ===========================================================================
:ReadTarget
set "CURTGT="
set "SUB="
for /f "tokens=2,*" %%A in ('fsutil reparsepoint query "%LINK%" 2^>nul ^| findstr /i /c:"Substitute Name:"') do set "SUB=%%B"
if not defined SUB exit /b 0
rem strip the \??\ reparse prefix to get a normal drive path.
rem Delayed expansion is required here: with "%SUB:...=%" the percent form is
rem expanded while the line is read, so it would pick up the value from the
rem PREVIOUS call rather than the one just assigned on the line above.
set "CURTGT=!SUB:\??\=!"
rem %%~fP makes it absolute and drops the trailing backslash, so that the
rem caller can compare it with plain string equality
if defined CURTGT for %%P in ("!CURTGT!") do set "CURTGT=%%~fP"
exit /b 0
rem ===========================================================================
rem  :PickBest "<dirname>" -- compare version numbers, replace BEST if larger
rem
rem  CALL is used to reuse code, so every routine works on global variables and
rem  must NOT use setlocal (values would not travel back to the caller).
rem  Comparison uses set /a and deliberately no zero padding, because set /a
rem  reads a leading zero as octal and fails on 08.
rem
rem  NOTE: the candidate is held in DNAME, never in CD - "%CD%" is a cmd
rem  dynamic variable holding the current working directory.
rem ===========================================================================
:PickBest
set "DNAME=%~1"
rem String substitution in the delayed-expansion family uses "!" at BOTH ends:
rem   !VAR:find=replace!
rem Writing "%" at the end (as this used to: !DNAME:app-=%) makes cmd treat
rem the trailing "%" as the start of a percent expansion, the substitution
rem never happens, and CV ends up holding the literal text "DNAME:app-=".
rem The debug output showed exactly that, which is why every version compared
rem equal and the first candidate always won.
set "CV=!DNAME:app-=!"
if not defined BEST (
set "BEST=!DNAME!"
goto PBEnd
)
rem split the current BEST version into B1..B4
rem Each variable is assigned from its own explicit token index. An earlier
rem version used "if not defined B1 set "B1=%%x"" and relied on the token
rem variables rotating as the for loop iterated; that mixes parse-time
rem (%%x) expansion with run-time ("if not defined") state and is fragile
rem inside a CALLed routine.
rem NOTE: every option of "for /f" must live inside ONE quoted string. Writing
rem for /f "tokens=1" delims=. %%x splits it into two parts and cmd reports
rem "delims was unexpected at this time."
set "BV=!BEST:app-=!"
set "B1=0" & set "B2=0" & set "B3=0" & set "B4=0"
for /f "tokens=1 delims=." %%x in ("!BV!") do set "B1=%%x"
for /f "tokens=2 delims=." %%x in ("!BV!") do set "B2=%%x"
for /f "tokens=3 delims=." %%x in ("!BV!") do set "B3=%%x"
for /f "tokens=4 delims=." %%x in ("!BV!") do set "B4=%%x"
rem split the candidate version into C1..C4
set "C1=0" & set "C2=0" & set "C3=0" & set "C4=0"
for /f "tokens=1 delims=." %%x in ("!CV!") do set "C1=%%x"
for /f "tokens=2 delims=." %%x in ("!CV!") do set "C2=%%x"
for /f "tokens=3 delims=." %%x in ("!CV!") do set "C3=%%x"
for /f "tokens=4 delims=." %%x in ("!CV!") do set "C4=%%x"
rem Segment by segment compare. Written flat on purpose: a chain of nested
rem if-blocks with goto in between is easy to break, and jumping into or
rem across block labels is exactly what caused ") was unexpected at this
rem time." earlier. Here every goto stays at the top level of the routine.
call :Seg !C1! !B1!
if "!CMP!"=="LT" goto PBEnd
if "!CMP!"=="GT" goto PBSet
call :Seg !C2! !B2!
if "!CMP!"=="LT" goto PBEnd
if "!CMP!"=="GT" goto PBSet
call :Seg !C3! !B3!
if "!CMP!"=="LT" goto PBEnd
if "!CMP!"=="GT" goto PBSet
call :Seg !C4! !B4!
if "!CMP!"=="GT" goto PBSet
rem All four segments are equal: keep the earlier one. Two directories with
rem the same version would be abnormal, and not overwriting is the safer
rem choice.
goto PBEnd
:PBSet
set "BEST=!DNAME!"
:PBEnd
exit /b 0
rem ===========================================================================
rem  :Seg <A> <B> -- numeric compare, result in CMP: GT / LT / EQ
rem
rem  The operands arrive as command line arguments. "%~1" is the correct way
rem  to read them: the tilde modifier belongs to the percent family only, so
rem  "!~1!" expands to nothing at all. That silently made both operands 0,
rem  every comparison returned EQ, and BEST stayed on the first candidate
rem  (it picked app-3.6.5 over app-3.6.6).
rem ===========================================================================
:Seg
set "SBA=%~1"
set "SBB=%~2"
if "!SBA!"=="" set "SBA=0"
if "!SBB!"=="" set "SBB=0"
rem "set /a X=X+0" normalises any stray leading zero, which set /a would
rem otherwise read as octal.
set /a "SBA=SBA+0" 2>nul
set /a "SBB=SBB+0" 2>nul
if !SBA! GTR !SBB! (set "CMP=GT") else if !SBA! LSS !SBB! (set "CMP=LT") else (set "CMP=EQ")
exit /b 0

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@echo off

rem ===========================================================================

rem GitHub Desktop - ghd-latest directory-link maintainer (pure batch)

rem

rem Usage:

rem ghd-app-latest.bat create/update the link as needed

rem ghd-app-latest.bat -CheckOnly report only, change nothing

rem ghd-app-latest.bat latest use a different link name

rem ghd-app-latest.bat -Debug extra tracing while diagnosing

rem

rem Exit code: 0 ok | 2 install not found | 3 refused | 4 link failed | 1 error

rem

rem NOTE: keep this file pure ASCII with NO byte order mark.

rem A BOM-less UTF-8 batch is read by cmd.exe byte by byte, and CJK

rem text gets chopped into fragments that are then parsed as commands

rem (it produced errors like "'URTGT' is not recognized"). All prompts

rem here are ASCII on purpose, so the file works under any code page.

rem

rem ---------------------------------------------------------------------------

rem Implementation notes (all native cmd, no PowerShell):

rem find install : reg query on uninstall keys, else %LOCALAPPDATA%

rem match names : pure string substitution, no findstr and no regex. A

rem caret-anchored /c:"^app-[0-9]$" never matches inside cmd,

rem whatever findstr really receives is not what it looks like.

rem pick version : split on dots, compare segment by segment numerically.

rem Never sort / compare as string - that puts 3.6.10 before

rem 3.6.9. Also never take the first entry of dir /o-n:

rem that is time-ordered and our own ghd-latest sorts first.

rem read target : fsutil reparsepoint query, parse the "Substitute Name"

rem line. Do NOT use "Print Name" - for a junction its

rem length is always 0.

rem create link : mklink /J (directory junction). No mklink /D fallback:

rem /D needs admin or developer mode, so it fails anyway.

rem delete link : rmdir, never with the recursive switch.

rem ---------------------------------------------------------------------------

setlocal EnableExtensions EnableDelayedExpansion

rem ===========================================================================

rem Parse arguments

rem ===========================================================================

rem The default link name is "ghd-latest", NOT "app-latest". Squirrel removes

rem stale version directories with a loose test for names CONTAINING "app-",

rem and its recursive delete does not recognise reparse points. A link named

rem app-latest therefore gets destroyed on the next GitHub Desktop update,

rem and the delete follows the junction into the real version directory and

rem removes files from it. That was observed happening on this machine.

rem "ghd-latest" contains no "app-" and stays outside that sweep entirely.

set "LINKNAME=ghd-latest"

set "CHECKONLY=0"

set "DEBUG=0"

:ParseArgs

if "%~1"=="" goto AfterArgs

if /i "%~1"=="-CheckOnly" (set "CHECKONLY=1" & shift & goto ParseArgs)

if /i "%~1"=="/CheckOnly" (set "CHECKONLY=1" & shift & goto ParseArgs)

if /i "%~1"=="-Debug" (set "DEBUG=1" & shift & goto ParseArgs)

if /i "%~1"=="/Debug" (set "DEBUG=1" & shift & goto ParseArgs)

set "LINKNAME=%~1"

shift

goto ParseArgs

:AfterArgs

if "%DEBUG%"=="1" echo (debug mode on)

set "RC=0"

set "E_NOFIND=2"

set "E_REFUSE=3"

set "E_LINKFAIL=4"

echo.

echo GitHub Desktop - ghd-latest link maintainer

echo --------------------------------------------

echo Link name: %LINKNAME%

rem ===========================================================================

rem Guard: the link name must not look like a version directory

rem

rem Done with substitution, not findstr. A caret-anchored regex on a cmd

rem command line is unreliable (see the note at :ConsiderDir), and a guard

rem that silently never fires is worse than no guard at all.

rem Rule: reject if the name starts with "app-" followed by a digit.

rem

rem Written as a subroutine that returns E_GUARD=1 when it must refuse, so

rem that no goto ever appears inside a nested if/for block.

rem ===========================================================================

set "E_GUARD=0"

call :CheckGuard

if "%E_GUARD%"=="1" (

echo x Link name "%LINKNAME%" clashes with the app-VERSION naming rule.

echo Refusing to run. Pick another name, e.g. ghd-app-latest.bat latest

set "RC=%E_REFUSE%"

goto Finish

)

rem ===========================================================================

rem 1. Locate the install root

rem ===========================================================================

echo.

echo [ Locate install ]

set "ROOT="

for /f "tokens=2,*" %%A in ('reg query "HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall" /s /v InstallLocation 2^>nul ^| findstr /i /c:"REG_SZ"') do (

if exist "%%~B\GitHubDesktop.exe" set "ROOT=%%~B"

)

if not defined ROOT if exist "%LOCALAPPDATA%\GitHubDesktop\GitHubDesktop.exe" set "ROOT=%LOCALAPPDATA%\GitHubDesktop"

if not defined ROOT (

echo x GitHub Desktop install directory not found.

echo Checked: HKCU uninstall InstallLocation and %%LOCALAPPDATA%%\GitHubDesktop

set "RC=%E_NOFIND%"

goto Finish

)

echo + Install root: %ROOT%

rem ===========================================================================

rem 2. Enumerate version directories

rem ===========================================================================

echo.

echo [ Version directories ]

set "CAND="

for /f "delims=" %%D in ('dir /b /ad "%ROOT%" 2^>nul') do call :ConsiderDir "%%D"

if not defined CAND (

echo x No complete and usable app-VERSION directory found.

set "RC=%E_NOFIND%"

goto Finish

)

rem ===========================================================================

rem 3. Pick the highest version (numeric, segment by segment)

rem ===========================================================================

echo.

set "BEST="

for %%D in (%CAND%) do call :PickBest "%%D"

if not defined BEST (

echo x Cannot determine the effective version.

set "RC=%E_NOFIND%"

goto Finish

)

echo + Effective version: !BEST!

rem ===========================================================================

rem 4. Inspect the existing link

rem ===========================================================================

echo.

echo [ Link state ]

set "LINK=%ROOT%\!LINKNAME!"

if exist "%LINK%\" (

call :ReadTarget

if defined CURTGT (

echo !LINKNAME! points to: !CURTGT!

if /i "!CURTGT!"=="%ROOT%\!BEST!" (

echo.

echo [ Result ]

echo Already up to date. Nothing to do.

set "RC=0"

goto Finish

)

echo * !LINKNAME! points to an older directory, repointing it to !BEST! ...

) else (

rem Target unreadable: if it is a link, it is broken (rebuild it);

rem if dir cannot even list it, it is a real directory (refuse).

dir /a:l "%LINK%" >nul 2>&1

if errorlevel 1 (

echo x "%LINKNAME%" exists but is NOT a link, it is a real directory.

echo Refusing to delete it. Please inspect it manually.

set "RC=%E_REFUSE%"

goto Finish

)

echo * Found a broken link, no readable target, rebuilding.

)

) else (

echo !LINKNAME! does not exist yet.

echo Creating it to point to !BEST! ...

)

if "%CHECKONLY%"=="1" (

echo.

echo [ Result ]

echo CheckOnly mode, nothing was changed.

echo It should point to: %ROOT%\!BEST!

set "RC=0"

goto Finish

)

rem ===========================================================================

rem 5. Risk warning

rem ===========================================================================

rem WARN=1 when the chosen link name contains app-, which puts the link

rem inside Squirrel's stale-version sweep. That is not theoretical: a link

rem named app-latest was destroyed by a real GitHub Desktop update, and the

rem recursive delete followed the junction and emptied the old version

rem directory it pointed at. The default ghd-latest avoids it entirely.

rem

rem When the chosen name IS out of range, also check whether a leftover link

rem from the old default is still sitting there, and say so.

set "WARN=0"

call :ContainsAppDash

if "%WARN%"=="1" (

echo.

echo [ Risk warning ]

echo * Squirrel removes old versions with a loose "name contains app-"

echo * test, not an exact app-DIGIT match, so "%LINKNAME%" is in range.

echo * A GitHub Desktop update can delete this link, and the recursive

echo * delete does not recognise reparse points, so it follows the link

echo * into the real version directory and removes files from it.

echo Observed happening with the previous name "app-latest".

echo Workaround: ghd-app-latest.bat latest

)

rem leftover check: the old default name is dangerous, flag it if still present

if not "%LINKNAME%"=="app-latest" (

if exist "%ROOT%\app-latest\" (

echo.

echo [ Leftover warning ]

echo * %ROOT%\app-latest still exists.

echo * It is inside the Squirrel sweep and its target directory may

echo * already have been emptied. Delete it, you will not need it.

)

rem ===========================================================================

rem 6. Rebuild the link

rem ===========================================================================

echo.

echo [ Update link ]

if exist "%LINK%\" (

rem rmdir removes the link entry itself.

rem Never add the recursive switch: it would empty the real target.

rmdir "%LINK%" >nul 2>&1

if exist "%LINK%\" (

echo x Failed to remove the old link, permission denied?

set "RC=%E_LINKFAIL%"

goto Finish

)

echo Old link removed, target directory untouched.

if not exist "%ROOT%\!BEST!\GitHubDesktop.exe" (

echo x Target vanished during the operation, aborting.

set "RC=%E_NOFIND%"

goto Finish

)

echo Creating directory junction with mklink /J ...

rem No mklink /D fallback: it needs admin or developer mode, so on a normal

rem user session it always fails. A junction is enough for a local NTFS dir.

mklink /J "%LINK%" "%ROOT%\!BEST!" >nul 2>&1

if not errorlevel 1 goto Verify

echo x mklink /J failed, check free disk space and permissions.

set "RC=%E_LINKFAIL%"

goto Finish

:Verify

call :ReadTarget

if not defined CURTGT (

echo x Cannot read the target after creating the link.

set "RC=%E_LINKFAIL%"

goto Finish

)

if /i not "%CURTGT%"=="%ROOT%\!BEST!" (

echo x Verification failed, actual target: %CURTGT%

set "RC=%E_LINKFAIL%"

goto Finish

)

if not exist "%LINK%\GitHubDesktop.exe" (

echo x GitHubDesktop.exe is not reachable through the link.

set "RC=%E_LINKFAIL%"

goto Finish

)

echo.

echo [ Result ]

echo + Path : %LINK%

echo + Target: !CURTGT!

echo + Verified: GitHubDesktop.exe is reachable through the link

set "RC=0"

goto Finish

rem ===========================================================================

rem Finish: single exit point, pause only when double-clicked

rem ===========================================================================

:Finish

echo.

if "%RC%"=="0" echo [OK] Done, the link points at the effective version.

if "%RC%"=="1" echo [ERR] Script error, see the details above.

if "%RC%"=="2" echo [ERR] GitHub Desktop install not found, nothing changed.

if "%RC%"=="3" echo [ERR] Refused on safety grounds, see the reason above.

if "%RC%"=="4" echo [ERR] Link creation failed, see the reason above.

rem CMDCMDLINE holds this file name when double-clicked, and does not when

rem invoked from an existing prompt - that is how we tell the two apart.

echo %CMDCMDLINE% | find /i "%~nx0" >nul && pause

endlocal & exit /b %RC%

rem ===========================================================================

rem :ContainsAppDash -- set WARN=1 when LINKNAME contains "app-"

rem ===========================================================================

:ContainsAppDash

set "WARN=0"

set "WCOPY=!LINKNAME!"

set "WFOUND="

:ContainsLoop

if "!WCOPY!"=="" goto ContainsDone

if not defined WFOUND (

if "!WCOPY:~0,4!"=="app-" set "WFOUND=1"

)

set "WCOPY=!WCOPY:~1!"

goto ContainsLoop

:ContainsDone

if defined WFOUND set "WARN=1"

exit /b 0

rem ===========================================================================

rem :CheckGuard -- set E_GUARD=1 when LINKNAME looks like app-<digit>...

rem ===========================================================================

:CheckGuard

set "E_GUARD=0"

set "GHEAD=!LINKNAME:~0,4!"

if not "!GHEAD!"=="app-" exit /b 0

set "GTAIL=!LINKNAME:~4!"

if "!GTAIL!"=="" exit /b 0

rem the character right after app- must be a digit

set "GONE=!GTAIL:~0,1!"

if "!GONE!"=="0" set "E_GUARD=1" & exit /b 0

if "!GONE!"=="1" set "E_GUARD=1" & exit /b 0

if "!GONE!"=="2" set "E_GUARD=1" & exit /b 0

if "!GONE!"=="3" set "E_GUARD=1" & exit /b 0

if "!GONE!"=="4" set "E_GUARD=1" & exit /b 0

if "!GONE!"=="5" set "E_GUARD=1" & exit /b 0

if "!GONE!"=="6" set "E_GUARD=1" & exit /b 0

if "!GONE!"=="7" set "E_GUARD=1" & exit /b 0

if "!GONE!"=="8" set "E_GUARD=1" & exit /b 0

if "!GONE!"=="9" set "E_GUARD=1" & exit /b 0

exit /b 0

rem ===========================================================================

rem :ConsiderDir "<dirname>" -- keep it in CAND if it is a usable version dir

rem

rem This is a subroutine on purpose. It used to be a label INSIDE the

rem "for /f ... do ( ... )" block, with "goto SkipD" as the skip path. That

rem is the classic batch trap: goto into a block label leaves the parser in

rem the wrong context, so the block's closing ")" is reported as

rem ") was unexpected at this time.". A goto that jumps OUT of a block is

rem fine; jumping INTO one is not. Using "call" keeps every goto outside.

rem

rem Same reason it does not use setlocal: it must append to the caller's

rem CAND list.

rem

rem NOTE: the argument is held in DNAME, never in CD. "%CD%" is a cmd dynamic

rem variable that expands to the current working directory.

rem

rem The name test uses string substitution, NOT findstr and NOT a regex.

rem Debug output proved that inside cmd a double quoted "/c:^app-[0-9][0-9.]*$"

rem never matches, whatever findstr receives is not what we think it gets

rem (caret and dollar are cmd metacharacters on that command line).

rem Substitution has no such ambiguity:

rem 1. must start with app-

rem 2. strip app-, the remainder must not be empty

rem 3. the remainder must consist only of digits and dots

rem Verified to accept exactly the same set as the old regex on real data,

rem plus it additionally rejects mixed case like APP-1.2.

rem ===========================================================================

:ConsiderDir

set "DNAME=%~1"

rem --- name test by substitution, see the note above ---

rem must begin with app-

if "!DNAME:~0,4!" neq "app-" exit /b 0

rem strip the app- prefix, the remainder must not be empty

set "TAIL=!DNAME:~4!"

if "!TAIL!"=="" exit /b 0

rem delete every digit and dot; whatever survives must be empty.

rem Written out longhand instead of a "for %%d in (...)" loop: this routine is

rem reached through CALL, and loop-variable expansion inside a called

rem subroutine is one of the places where it is easy to get the wrong value.

set "REST=!TAIL!"

set "REST=!REST:0=!"

set "REST=!REST:1=!"

set "REST=!REST:2=!"

set "REST=!REST:3=!"

set "REST=!REST:4=!"

set "REST=!REST:5=!"

set "REST=!REST:6=!"

set "REST=!REST:7=!"

set "REST=!REST:8=!"

set "REST=!REST:9=!"

set "REST=!REST:.=!"

if not "!REST!"=="" exit /b 0

if not exist "!ROOT!\!DNAME!\GitHubDesktop.exe" exit /b 0

if exist "!ROOT!\!DNAME!\.dead" exit /b 0

if exist "!ROOT!\!DNAME!\.not-finished" exit /b 0

set "CAND=!CAND! !DNAME!"

echo !DNAME!

exit /b 0

rem ===========================================================================

rem :ReadTarget -- read the reparse point target of %LINK% into CURTGT

rem

rem fsutil prints:

rem Substitute Name: \??\C:\path\to\app-3.6.6

rem tokens=2,* skips the two words "Substitute" and "Name:", so %%B is the

rem path. The "Print Name" line is unusable, its length is 0 for junctions.

rem Do NOT use setlocal here, CURTGT could not reach the caller.

rem ===========================================================================

:ReadTarget

set "CURTGT="

set "SUB="

for /f "tokens=2,*" %%A in ('fsutil reparsepoint query "%LINK%" 2^>nul ^| findstr /i /c:"Substitute Name:"') do set "SUB=%%B"

if not defined SUB exit /b 0

rem strip the \??\ reparse prefix to get a normal drive path.

rem Delayed expansion is required here: with "%SUB:...=%" the percent form is

rem expanded while the line is read, so it would pick up the value from the

rem PREVIOUS call rather than the one just assigned on the line above.

set "CURTGT=!SUB:\??\=!"

rem %%~fP makes it absolute and drops the trailing backslash, so that the

rem caller can compare it with plain string equality

if defined CURTGT for %%P in ("!CURTGT!") do set "CURTGT=%%~fP"

exit /b 0

rem ===========================================================================

rem :PickBest "<dirname>" -- compare version numbers, replace BEST if larger

rem

rem CALL is used to reuse code, so every routine works on global variables and

rem must NOT use setlocal (values would not travel back to the caller).

rem Comparison uses set /a and deliberately no zero padding, because set /a

rem reads a leading zero as octal and fails on 08.

rem

rem NOTE: the candidate is held in DNAME, never in CD - "%CD%" is a cmd

rem dynamic variable holding the current working directory.

rem ===========================================================================

:PickBest

set "DNAME=%~1"

rem String substitution in the delayed-expansion family uses "!" at BOTH ends:

rem !VAR:find=replace!

rem Writing "%" at the end (as this used to: !DNAME:app-=%) makes cmd treat

rem the trailing "%" as the start of a percent expansion, the substitution

rem never happens, and CV ends up holding the literal text "DNAME:app-=".

rem The debug output showed exactly that, which is why every version compared

rem equal and the first candidate always won.

set "CV=!DNAME:app-=!"

if not defined BEST (

set "BEST=!DNAME!"

goto PBEnd

)

rem split the current BEST version into B1..B4

rem Each variable is assigned from its own explicit token index. An earlier

rem version used "if not defined B1 set "B1=%%x"" and relied on the token

rem variables rotating as the for loop iterated; that mixes parse-time

rem (%%x) expansion with run-time ("if not defined") state and is fragile

rem inside a CALLed routine.

rem NOTE: every option of "for /f" must live inside ONE quoted string. Writing

rem for /f "tokens=1" delims=. %%x splits it into two parts and cmd reports

rem "delims was unexpected at this time."

set "BV=!BEST:app-=!"

set "B1=0" & set "B2=0" & set "B3=0" & set "B4=0"

for /f "tokens=1 delims=." %%x in ("!BV!") do set "B1=%%x"

for /f "tokens=2 delims=." %%x in ("!BV!") do set "B2=%%x"

for /f "tokens=3 delims=." %%x in ("!BV!") do set "B3=%%x"

for /f "tokens=4 delims=." %%x in ("!BV!") do set "B4=%%x"

rem split the candidate version into C1..C4

set "C1=0" & set "C2=0" & set "C3=0" & set "C4=0"

for /f "tokens=1 delims=." %%x in ("!CV!") do set "C1=%%x"

for /f "tokens=2 delims=." %%x in ("!CV!") do set "C2=%%x"

for /f "tokens=3 delims=." %%x in ("!CV!") do set "C3=%%x"

for /f "tokens=4 delims=." %%x in ("!CV!") do set "C4=%%x"

rem Segment by segment compare. Written flat on purpose: a chain of nested

rem if-blocks with goto in between is easy to break, and jumping into or

rem across block labels is exactly what caused ") was unexpected at this

rem time." earlier. Here every goto stays at the top level of the routine.

call :Seg !C1! !B1!

if "!CMP!"=="LT" goto PBEnd

if "!CMP!"=="GT" goto PBSet

call :Seg !C2! !B2!

if "!CMP!"=="LT" goto PBEnd

if "!CMP!"=="GT" goto PBSet

call :Seg !C3! !B3!

if "!CMP!"=="LT" goto PBEnd

if "!CMP!"=="GT" goto PBSet

call :Seg !C4! !B4!

if "!CMP!"=="GT" goto PBSet

rem All four segments are equal: keep the earlier one. Two directories with

rem the same version would be abnormal, and not overwriting is the safer

rem choice.

goto PBEnd

:PBSet

set "BEST=!DNAME!"

:PBEnd

exit /b 0

rem ===========================================================================

rem :Seg <A> <B> -- numeric compare, result in CMP: GT / LT / EQ

rem

rem The operands arrive as command line arguments. "%~1" is the correct way

rem to read them: the tilde modifier belongs to the percent family only, so

rem "!~1!" expands to nothing at all. That silently made both operands 0,

rem every comparison returned EQ, and BEST stayed on the first candidate

rem (it picked app-3.6.5 over app-3.6.6).

rem ===========================================================================

:Seg

set "SBA=%~1"

set "SBB=%~2"

if "!SBA!"=="" set "SBA=0"

if "!SBB!"=="" set "SBB=0"

rem "set /a X=X+0" normalises any stray leading zero, which set /a would

rem otherwise read as octal.

set /a "SBA=SBA+0" 2>nul

set /a "SBB=SBB+0" 2>nul

if !SBA! GTR !SBB! (set "CMP=GT") else if !SBA! LSS !SBB! (set "CMP=LT") else (set "CMP=EQ")

exit /b 0

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张三太爷

看前面，黑洞洞

GitHub Desktop 团队，也是草台班子

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