Resolve :PAGER' if its path contains spaces (#8571)

src/System.Management.Automation/engine/InitialSessionState.cs

@@ -4177,10 +4177,36 @@ param(
     }
     elseif ($help -ne $null)
     {
+        $customPagerCommand = """"
+        $customPagerCommandArgs = """"
+        $customPagerCommandLine = """"
+
+        if ($env:PAGER)
+        {
+            $customPagerCommandLine = $env:PAGER
+
+            # Split the command line into tokens, respecting quoting.
+            $customPagerCommand, $customPagerCommandArgs = & { Write-Output -- $customPagerCommandLine }
+
+            # See if the first token refers to a known command (executable),
+            # and if not, see if the command line as a whole is an executable path.
+            $cmds = Get-Command $customPagerCommand, $customPagerCommandLine -ErrorAction Ignore
+            if (-not $cmds) {
+                # Custom command is invalid; ignore it, but issue a warning.
+                Write-Warning ""Ignoring invalid custom-paging utility command line specified in `$env:PAGER: $customPagerCommandLine""
+                $customPagerCommand = $null # use default command
+            }
+            elseif ($cmds.Count -eq 1 -and $cmds[0].Source -eq $customPagerCommandLine) {
+                # The full command line is an unquoted path to an existing executable
+                # with embedded spaces.
+                $customPagerCommand = $customPagerCommandLine
+                $customPagerCommandArgs = $null
+            }
+        }
+
         # Respect PAGER, use more on Windows, and use less on Linux
-        $moreCommand,$moreArgs = $env:PAGER -split '\s+'
-        if ($moreCommand) {
-            $help | & $moreCommand $moreArgs
+        if ($customPagerCommand) {
+            $help | & $customPagerCommand $customPagerCommandArgs
         } elseif ($IsWindows) {
             $help | more.com
         } else {

test/powershell/engine/Help/HelpSystem.Tests.ps1

@@ -513,3 +513,34 @@ Describe "Help failure cases" -Tags Feature {
         { & $command foobar -ErrorAction Stop } | Should -Throw -ErrorId "HelpNotFound,Microsoft.PowerShell.Commands.GetHelpCommand"
     }
 }
+
+Describe 'help renders when using a PAGER with a space in the path' -Tags 'CI' {
+    BeforeAll {
+        $fakePager = @'
+        param(
+            [Parameter]
+            $customCommandArgs,
+
+            [Parameter(ValueFromPipelineByPropertyName)]
+            $Name
+        )
+
+        $b = [System.Text.Encoding]::UTF8.GetBytes($Name)
+        return [System.Convert]::ToBase64String($b)
+'@
+        $fakePagerFolder = Join-Path $TestDrive "path with space"
+        $fakePagerPath = Join-Path $fakePagerFolder "fakepager.ps1"
+        New-Item -ItemType File -Path $fakePagerPath -Force > $null
+        Set-Content -Path $fakePagerPath -Value $fakePager
+
+        $SavedEnvPager = $env:PAGER
+        $env:PAGER = $fakePagerPath
+    }
+    AfterAll {
+        $env:PAGER = $SavedEnvPager
+    }
+
+    It 'help renders when using a PAGER with a space in the path' {
+        help Get-Command | Should -Be "R2V0LUNvbW1hbmQ="
+    }
+}