Support locking windows

.github/workflows/prechecks.yml

@@ -40,7 +40,7 @@ jobs:
     # Check that __slots__ are used properly
     - name: slotscheck
       run: |
-        ./bin/spack python -m slotscheck --exclude-modules="spack.test|spack.vendor|spack.new_installer_windows" lib/spack/spack/
+        ./bin/spack python -m slotscheck --exclude-modules="spack.test|spack.vendor|spack.new_installer_windows|spack.util.lock_windows" lib/spack/spack/
 
   # Run style checks on the files that have been changed
   style:

etc/spack/defaults/windows/config.yaml

@@ -1,5 +1,4 @@
 config:
-  locks: false
   build_stage::
     - '$user_cache_path/stage'
   stage_name: '{name}-{version}-{hash:7}'

lib/spack/docs/conf.py

@@ -97,6 +97,7 @@
         "_spack_root/lib/spack/spack/test",
         "_spack_root/lib/spack/spack/package.py",
         "_spack_root/lib/spack/spack/new_installer_windows.py",
+        "_spack_root/lib/spack/spack/util/lock_windows.py",
     ]
 )
 sphinx_apidoc(

lib/spack/spack/test/conftest.py

@@ -539,8 +539,11 @@ def ignore_stage_files():
 
     Used to track which leftover files in the stage have been seen.
     """
-    # to start with, ignore the .lock file at the stage root.
-    return set([".lock", spack.stage._source_path_subdir, "build_cache"])
+    # to start with, ignore the .lock file at the stage root, and its Windows-only gate lock
+    # sidecar (see spack.util.lock_windows.WindowsBackend._upgrade_to_write). Neither is ever
+    # explicitly unlinked for stage locks; they're only ever removed along with the whole stage
+    # directory.
+    return set([".lock", ".lock.gate_lock", spack.stage._source_path_subdir, "build_cache"])
 
 
 def remove_whatever_it_is(path):