Allow configurable stage names (#36509)

Add `config:stage_name` which is a Spec format string that can
customize the names of stages created by Spack. This was primarily
created to allow generating shorter stage names on Windows (along
with `config:build_stage`, this can be used to create stages with
short absolute paths).

By default, this is not set and the prior name stage format is used.

This also removes the username component that is always added to
Stage paths on Windows (if users want to include this, they can
add it to the `build_stage`).

etc/spack/defaults/windows/config.yaml

@@ -3,3 +3,4 @@ config:
   concretizer: clingo
   build_stage::
     - '$spack/.staging'
+  stage_name: '{name}-{version}-{hash:7}'

lib/spack/spack/package_base.py

@@ -57,7 +57,7 @@
 from spack.filesystem_view import YamlFilesystemView
 from spack.install_test import TestFailure, TestSuite
 from spack.installer import InstallError, PackageInstaller
-from spack.stage import ResourceStage, Stage, StageComposite, stage_prefix
+from spack.stage import ResourceStage, Stage, StageComposite, compute_stage_name
 from spack.util.executable import ProcessError, which
 from spack.util.package_hash import package_hash
 from spack.util.prefix import Prefix
@@ -1022,8 +1022,7 @@ def _make_root_stage(self, fetcher):
         )
         # Construct a path where the stage should build..
         s = self.spec
-        stage_name = "{0}{1}-{2}-{3}".format(stage_prefix, s.name, s.version, s.dag_hash())
-
+        stage_name = compute_stage_name(s)
         stage = Stage(
             fetcher,
             mirror_paths=mirror_paths,

lib/spack/spack/schema/config.py

@@ -61,6 +61,7 @@
             "build_stage": {
                 "oneOf": [{"type": "string"}, {"type": "array", "items": {"type": "string"}}]
             },
+            "stage_name": {"type": "string"},
             "test_stage": {"type": "string"},
             "extensions": {"type": "array", "items": {"type": "string"}},
             "template_dirs": {"type": "array", "items": {"type": "string"}},

lib/spack/spack/stage.py

@@ -35,6 +35,7 @@
 import spack.fetch_strategy as fs
 import spack.mirror
 import spack.paths
+import spack.spec
 import spack.util.lock
 import spack.util.path as sup
 import spack.util.pattern as pattern
@@ -49,6 +50,13 @@
 stage_prefix = "spack-stage-"
 
 
+def compute_stage_name(spec):
+    """Determine stage name given a spec"""
+    default_stage_structure = "spack-stage-{name}-{version}-{hash}"
+    stage_name_structure = spack.config.get("config:stage_name", default=default_stage_structure)
+    return spec.format(format_string=stage_name_structure)
+
+
 def create_stage_root(path: str) -> None:
     """Create the stage root directory and ensure appropriate access perms."""
     assert os.path.isabs(path) and len(path.strip()) > 1
@@ -150,7 +158,10 @@ def _resolve_paths(candidates):
 
         # Ensure the path is unique per user.
         can_path = sup.canonicalize_path(path)
-        if user not in can_path:
+        # When multiple users share a stage root, we can avoid conflicts between
+        # them by adding a per-user subdirectory.
+        # Avoid doing this on Windows to keep stage absolute path as short as possible.
+        if user not in can_path and not sys.platform == "win32":
             can_path = os.path.join(can_path, user)
 
         paths.append(can_path)

lib/spack/spack/test/stage.py

@@ -765,7 +765,10 @@ def test_resolve_paths(self):
 
         # resolved path without user appends user
         paths = [os.path.join(os.path.sep, "a", "b", "c")]
+        can_paths = [paths[0]]
         user = getpass.getuser()
+
+        if sys.platform != "win32":
             can_paths = [os.path.join(paths[0], user)]
         assert spack.stage._resolve_paths(paths) == can_paths
 
@@ -789,7 +792,7 @@ def test_resolve_paths(self):
             res_paths[1] = can_tempdir
             res_paths[2] = os.path.join(can_tempdir, user)
             res_paths[3] = os.path.join(can_tempdir, "stage", user)
-        else:
+        elif sys.platform != "win32":
             res_paths[0] = os.path.join(res_paths[0], user)
 
         assert spack.stage._resolve_paths(paths) == res_paths