traverse: w/o deptype (#42345)

Add the empty deptype `spack.deptypes.NONE`.

Test the case `traverse_nodes(deptype=spack.deptypes.NONE)` to not
traverse dependencies, only de-duplicate.

Use the construct in environment views that otherwise would branch on
whether deps are enabled or not.

3 files changed, 25 insertions, 14 deletions

diff --git a/lib/spack/spack/deptypes.py b/lib/spack/spack/deptypes.py
index af196bd4ad..df965a87f1 100644
--- a/lib/spack/spack/deptypes.py
+++ b/lib/spack/spack/deptypes.py
@@ -36,6 +36,9 @@ ALL: DepFlag = BUILD | LINK | RUN | TEST
 #: Default dependency type if none is specified
 DEFAULT: DepFlag = BUILD | LINK
 
+#: A flag with no dependency types set
+NONE: DepFlag = 0
+
 #: An iterator of all flag components
 ALL_FLAGS: Tuple[DepFlag, DepFlag, DepFlag, DepFlag] = (BUILD, LINK, RUN, TEST)
 
diff --git a/lib/spack/spack/environment/environment.py b/lib/spack/spack/environment/environment.py
index 2a6cc6e774..634c1925d3 100644
--- a/lib/spack/spack/environment/environment.py
+++ b/lib/spack/spack/environment/environment.py
@@ -21,7 +21,6 @@ from typing import Dict, Iterable, List, Optional, Set, Tuple, Union
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
 import llnl.util.tty.color as clr
-from llnl.util.lang import dedupe
 from llnl.util.link_tree import ConflictingSpecsError
 from llnl.util.symlink import symlink
 
@@ -663,27 +662,23 @@ class ViewDescriptor:
 
         return True
 
-    def specs_for_view(self, concretized_root_specs):
+    def specs_for_view(self, concrete_roots: List[Spec]) -> List[Spec]:
         """
         From the list of concretized user specs in the environment, flatten
         the dags, and filter selected, installed specs, remove duplicates on dag hash.
         """
-        # With deps, requires traversal
-        if self.link == "all" or self.link == "run":
-            deptype = ("run") if self.link == "run" else ("link", "run")
-            specs = list(
-                traverse.traverse_nodes(
-                    concretized_root_specs, deptype=deptype, key=traverse.by_dag_hash
-                )
-            )
+        if self.link == "all":
+            deptype = dt.LINK | dt.RUN
+        elif self.link == "run":
+            deptype = dt.RUN
         else:
-            specs = list(dedupe(concretized_root_specs, key=traverse.by_dag_hash))
+            deptype = dt.NONE
+
+        specs = traverse.traverse_nodes(concrete_roots, deptype=deptype, key=traverse.by_dag_hash)
 
         # Filter selected, installed specs
         with spack.store.STORE.db.read_transaction():
-            specs = [s for s in specs if s in self and s.installed]
-
-        return specs
+            return [s for s in specs if s in self and s.installed]
 
     def regenerate(self, concretized_root_specs):
         specs = self.specs_for_view(concretized_root_specs)
diff --git a/lib/spack/spack/test/traverse.py b/lib/spack/spack/test/traverse.py
index 8e440f93fb..0876c65cc2 100644
--- a/lib/spack/spack/test/traverse.py
+++ b/lib/spack/spack/test/traverse.py
@@ -395,3 +395,16 @@ def test_traverse_edges_topo(abstract_specs_toposort):
         out_edge_indices = [i for (i, (parent, child)) in enumerate(edges) if node == parent]
         if in_edge_indices and out_edge_indices:
             assert max(in_edge_indices) < min(out_edge_indices)
+
+
+def test_traverse_nodes_no_deps(abstract_specs_dtuse):
+    """Traversing nodes without deps should be the same as deduplicating the input specs. This may
+    not look useful, but can be used to avoid a branch on the call site in which it's otherwise
+    easy to forget to deduplicate input specs."""
+    inputs = [
+        abstract_specs_dtuse["dtuse"],
+        abstract_specs_dtuse["dtlink5"],
+        abstract_specs_dtuse["dtuse"],  # <- duplicate
+    ]
+    outputs = [x for x in traverse.traverse_nodes(inputs, deptype=dt.NONE)]
+    assert outputs == [abstract_specs_dtuse["dtuse"], abstract_specs_dtuse["dtlink5"]]