fix(commandDiscovery): 修复在 PATH 为空时命令解析失败的问题

- 为 PathExtValue、PathValue 等参数添加 AllowEmptyString() 属性，允许空字符串输入
- 在测试中预先获取 chmod 命令的绝对路径，避免因临时覆写 PATH 导致 Unix 下创建测试命令失败

Author: mudssky

psutils/modules/commandDiscovery.psm1

@@ -68,6 +68,7 @@ function Get-ExecutableCommandExtensions {
         [Parameter(Mandatory)]
         [string]$Name,
         [Parameter(Mandatory)]
+        [AllowEmptyString()]
         [string]$PathExtValue
     )
 
@@ -107,6 +108,7 @@ function Get-ExecutableCommandSearchPaths {
     [CmdletBinding()]
     param(
         [Parameter(Mandatory)]
+        [AllowEmptyString()]
         [string]$PathValue
     )
 
@@ -197,6 +199,7 @@ function Resolve-ExecutableCommand {
         [Parameter(Mandatory)]
         [string[]]$SearchPaths,
         [Parameter(Mandatory)]
+        [AllowEmptyString()]
         [string]$PathExtValue,
         [switch]$AllMatches
     )
@@ -257,6 +260,7 @@ function Resolve-ExecutableCommandsBatch {
         [Parameter(Mandatory)]
         [string[]]$SearchPaths,
         [Parameter(Mandatory)]
+        [AllowEmptyString()]
         [string]$PathExtValue,
         [switch]$AllMatches
     )

psutils/tests/commandDiscovery.Tests.ps1

@@ -2,6 +2,8 @@ BeforeAll {
     Import-Module "$PSScriptRoot\..\modules\commandDiscovery.psm1" -Force
     $script:OriginalPath = [Environment]::GetEnvironmentVariable('PATH', 'Process')
     $script:OriginalPathExt = [Environment]::GetEnvironmentVariable('PATHEXT', 'Process')
+    # 测试会临时覆写 PATH，因此在进入各个用例前先解析 chmod 的绝对路径，避免 Unix 下创建测试命令失败。
+    $script:ChmodPath = if ($IsWindows) { $null } else { (Get-Command chmod -ErrorAction Stop).Source }
 }
 
 AfterAll {
@@ -26,7 +28,7 @@ function global:New-TestExecutableCommand {
 
     $commandPath = Join-Path $Directory $Name
     Set-Content -Path $commandPath -Value "#!/usr/bin/env sh`necho ok" -Encoding ascii
-    & chmod +x $commandPath
+    & $script:ChmodPath +x $commandPath
     return $commandPath
 }