env: compute env mods only for installed roots (#40997)

And improve the error message (load vs unload).

Of course you could have some uninstalled dependency too, but as long as
it doesn't implement `setup_run_environment` etc, I don't think it hurts
to attempt to load the root anyways, given that failure to do so is a
warning, not a fatal error.

lib/spack/spack/environment/environment.py

@@ -1739,11 +1739,14 @@ def _env_modifications_for_view(
         self, view: ViewDescriptor, reverse: bool = False
     ) -> spack.util.environment.EnvironmentModifications:
         try:
-            mods = uenv.environment_modifications_for_specs(*self.concrete_roots(), view=view)
+            with spack.store.STORE.db.read_transaction():
+                installed_roots = [s for s in self.concrete_roots() if s.installed]
+            mods = uenv.environment_modifications_for_specs(*installed_roots, view=view)
         except Exception as e:
             # Failing to setup spec-specific changes shouldn't be a hard error.
             tty.warn(
-                "couldn't load runtime environment due to {}: {}".format(e.__class__.__name__, e)
+                f"could not {'unload' if reverse else 'load'} runtime environment due "
+                f"to {e.__class__.__name__}: {e}"
             )
             return spack.util.environment.EnvironmentModifications()
         return mods.reversed() if reverse else mods

lib/spack/spack/test/cmd/env.py

@@ -284,7 +284,7 @@ def setup_error(pkg, env):
 
     _, err = capfd.readouterr()
     assert "cmake-client had issues!" in err
-    assert "Warning: couldn't load runtime environment" in err
+    assert "Warning: could not load runtime environment" in err
 
 
 def test_activate_adds_transitive_run_deps_to_path(install_mockery, mock_fetch, monkeypatch):
@@ -502,12 +502,12 @@ def test_env_activate_broken_view(
     # test that Spack detects the missing package and fails gracefully
     with spack.repo.use_repositories(mock_custom_repository):
         wrong_repo = env("activate", "--sh", "test")
-        assert "Warning: couldn't load runtime environment" in wrong_repo
+        assert "Warning: could not load runtime environment" in wrong_repo
         assert "Unknown namespace: builtin.mock" in wrong_repo
 
     # test replacing repo fixes it
     normal_repo = env("activate", "--sh", "test")
-    assert "Warning: couldn't load runtime environment" not in normal_repo
+    assert "Warning: could not load runtime environment" not in normal_repo
     assert "Unknown namespace: builtin.mock" not in normal_repo
 
 

lib/spack/spack/user_environment.py

@@ -11,6 +11,7 @@
 
 import spack.build_environment
 import spack.config
+import spack.error
 import spack.spec
 import spack.util.environment as environment
 import spack.util.prefix as prefix