CI: use a Dev Drive to improve Windows I/O performance

.github/workflows/ci.yml

@@ -112,14 +112,15 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        os: [ubuntu-latest, macos-13, macos-latest]
+        os: [ubuntu-latest]
+        # os: [ubuntu-latest, macos-13, macos-latest]
         python:
           - "3.8"
-          - "3.9"
-          - "3.10"
-          - "3.11"
-          - "3.12"
-          - "3.13"
+        #   - "3.9"
+        #   - "3.10"
+        #   - "3.11"
+        #   - "3.12"
+        #   - "3.13"
 
     steps:
       - uses: actions/checkout@v4
@@ -162,7 +163,7 @@ jobs:
     name: tests / ${{ matrix.python }} / ${{ matrix.os }} / ${{ matrix.group }}
     runs-on: ${{ matrix.os }}-latest
 
-    needs: [packaging, determine-changes]
+    needs: [determine-changes]
     if: >-
       needs.determine-changes.outputs.tests == 'true' ||
       github.event_name != 'pull_request'
@@ -189,13 +190,13 @@ jobs:
           python-version: ${{ matrix.python }}
           allow-prereleases: true
 
-      # We use C:\Temp (which is already available on the worker)
-      # as a temporary directory for all of the tests because the
-      # default value (under the user dir) is more deeply nested
-      # and causes tests to fail with "path too long" errors.
+      - name: Create a Dev Drive
+        run: |
+          ./tools/ci/devdrive.ps1 -Drive R -Size 5GB
+          mkdir R:\Temp
+          echo "TEMP=R:\\Temp" >> $env:GITHUB_ENV
+
       - run: pip install nox
-        env:
-          TEMP: "C:\\Temp"
 
       # Main check
       - name: Run unit tests
@@ -204,26 +205,20 @@ jobs:
           nox -s test-${{ matrix.python }} --
           -m unit
           --verbose --numprocesses auto --showlocals
-        env:
-          TEMP: "C:\\Temp"
 
       - name: Run integration tests (group 1)
         if: matrix.group == 1
         run: >-
           nox -s test-${{ matrix.python }} --
           -m integration -k "not test_install"
           --verbose --numprocesses auto --showlocals
-        env:
-          TEMP: "C:\\Temp"
 
       - name: Run integration tests (group 2)
         if: matrix.group == 2
         run: >-
           nox -s test-${{ matrix.python }} --
           -m integration -k "test_install"
           --verbose --numprocesses auto --showlocals
-        env:
-          TEMP: "C:\\Temp"
 
   tests-zipapp:
     name: tests / zipapp

tools/ci/devdrive.ps1

@@ -0,0 +1,39 @@
+# A Powershell script to create a Dev Drive which tends to have significantly better
+# performance in developer workloads. The goal is improve pip's Windows CI times.
+#
+# The implementation was borrowed from the uv project which also use a Dev Drive for
+# better CI performance: https://github.com/astral-sh/uv/pull/3522
+#
+# Windows docs:
+#   https://learn.microsoft.com/en-us/windows/dev-drive/
+# Related GHA reports:
+#   https://github.com/actions/runner-images/issues/7320 (Windows slowness report)
+#   https://github.com/actions/runner-images/issues/8698 (feature request for
+#     preprovisioned Dev Drives)
+
+[CmdletBinding()]
+param(
+    [Parameter(Mandatory=$true,
+    HelpMessage="Drive letter to use for the Dev Drive")]
+    [String]$drive,
+    [Parameter(Mandatory=$true,
+    HelpMessage="Size to allocate to the Dev Drive")]
+    [UInt64]$size
+)
+$ErrorActionPreference = "Stop"
+
+$OSVersion = [Environment]::OSVersion.Version
+$Partition = New-VHD -Path C:/pip_dev_drive.vhdx -SizeBytes $size |
+          Mount-VHD -Passthru |
+          Initialize-Disk -Passthru |
+          New-Partition -DriveLetter $drive -UseMaximumSize
+# Dev Drives aren't supported on all GHA Windows runners, in which case fallback to
+# a ReFS disk which still offer performance gains.
+if ($OSVersion -ge (New-Object 'Version' 10.0.22621)) {
+    Write-Output "Dev Drives are supported, one will be created at ${drive}:"
+    $Volume = ($Partition | Format-Volume -DevDrive -Confirm:$false -Force)
+} else {
+    Write-Output "Dev Drives are unsupported, only creating a ReFS disk at ${drive}:"
+    $Volume = ($Partition | Format-Volume -FileSystem ReFS -Confirm:$false -Force)
+}
+Write-Output $Volume