spec.py: more virtuals=... type hints (#49753)

Deal with the "issue" that passing a str instance does not cause a
type check failure, because str is a subset of Sequence[str] and
Iterable[str]. Instead fix it by special casing the str instance.

lib/spack/spack/solver/asp.py

@@ -3834,7 +3834,7 @@ def virtual_on_edge(self, parent_node, provider_node, virtual):
         provider_spec = self._specs[provider_node]
         dependencies = [x for x in dependencies if id(x.spec) == id(provider_spec)]
         assert len(dependencies) == 1, f"{virtual}: {provider_node.pkg}"
-        dependencies[0].update_virtuals((virtual,))
+        dependencies[0].update_virtuals(virtual)
 
     def reorder_flags(self):
         """For each spec, determine the order of compiler flags applied to it.

lib/spack/spack/spec.py

@@ -754,11 +754,17 @@ def update_deptypes(self, depflag: dt.DepFlag) -> bool:
         self.depflag = new
         return True
 
-    def update_virtuals(self, virtuals: Iterable[str]) -> bool:
+    def update_virtuals(self, virtuals: Union[str, Iterable[str]]) -> bool:
         """Update the list of provided virtuals"""
         old = self.virtuals
-        self.virtuals = tuple(sorted(set(virtuals).union(self.virtuals)))
-        return old != self.virtuals
+        if isinstance(virtuals, str):
+            union = {virtuals, *self.virtuals}
+        else:
+            union = {*virtuals, *self.virtuals}
+        if len(union) == len(old):
+            return False
+        self.virtuals = tuple(sorted(union))
+        return True
 
     def copy(self) -> "DependencySpec":
         """Return a copy of this edge"""
@@ -1041,7 +1047,7 @@ def select(
             parent: name of the parent package
             child: name of the child package
             depflag: allowed dependency types in flag form
-            virtuals: list of virtuals on the edge
+            virtuals: list of virtuals or specific virtual on the edge
         """
         if not depflag:
             return []
@@ -1590,7 +1596,11 @@ def _get_dependency(self, name):
         return deps[0]
 
     def edges_from_dependents(
-        self, name=None, depflag: dt.DepFlag = dt.ALL, *, virtuals: Optional[List[str]] = None
+        self,
+        name=None,
+        depflag: dt.DepFlag = dt.ALL,
+        *,
+        virtuals: Optional[Union[str, Sequence[str]]] = None,
     ) -> List[DependencySpec]:
         """Return a list of edges connecting this node in the DAG
         to parents.

lib/spack/spack/test/spec_semantics.py

@@ -1948,6 +1948,18 @@ def test_edge_equality_does_not_depend_on_virtual_order():
     assert tuple(sorted(edge2.virtuals)) == edge1.virtuals
 
 
+def test_update_virtuals():
+    parent, child = Spec("parent"), Spec("child")
+    edge = DependencySpec(parent, child, depflag=0, virtuals=("mpi", "lapack"))
+    assert edge.update_virtuals("blas")
+    assert edge.virtuals == ("blas", "lapack", "mpi")
+    assert edge.update_virtuals(("c", "fortran", "mpi", "lapack"))
+    assert edge.virtuals == ("blas", "c", "fortran", "lapack", "mpi")
+    assert not edge.update_virtuals("mpi")
+    assert not edge.update_virtuals(("c", "fortran", "mpi", "lapack"))
+    assert edge.virtuals == ("blas", "c", "fortran", "lapack", "mpi")
+
+
 def test_virtual_queries_work_for_strings_and_lists():
     """Ensure that ``dependencies()`` works with both virtuals=str and virtuals=[str, ...]."""
     parent, child = Spec("parent"), Spec("child")