Fix bugs in spack dependencies command (#7435)

- transitive dependencies were not being handled correctly

- restructure code to do recursion and mark visited packages properly

- add `-V` option to *not* expand virtuals in spack dependencies

lib/spack/spack/cmd/dependencies.py

@@ -43,7 +43,10 @@ def setup_parser(subparser):
         "instead of possible dependencies of a package.")
     subparser.add_argument(
         '-t', '--transitive', action='store_true', default=False,
-        help="Show all transitive dependencies.")
+        help="show all transitive dependencies")
+    subparser.add_argument(
+        '-V', '--no-expand-virtuals', action='store_false', default=True,
+        dest="expand_virtuals", help="do not expand virtual dependencies")
     subparser.add_argument(
         'spec', nargs=argparse.REMAINDER, help="spec or package name")
 
@@ -76,7 +79,8 @@ def dependencies(parser, args):
         dependencies = set()
         for pkg in packages:
             dependencies.update(
-                set(pkg.possible_dependencies(args.transitive)))
+                set(pkg.possible_dependencies(
+                    args.transitive, args.expand_virtuals)))
 
         if spec.name in dependencies:
             dependencies.remove(spec.name)

lib/spack/spack/graph.py

@@ -543,7 +543,9 @@ def q(string):
 
     # Static graph includes anything a package COULD depend on.
     if static:
-        names = set.union(*[s.package.possible_dependencies() for s in specs])
+        names = set.union(*[
+            s.package.possible_dependencies(expand_virtuals=False)
+            for s in specs])
         specs = [Spec(name) for name in names]
 
     labeled = set()

lib/spack/spack/package.py

@@ -627,31 +627,40 @@ def __init__(self, spec):
 
         super(PackageBase, self).__init__()
 
-    def possible_dependencies(self, transitive=True, visited=None):
-        """Return set of possible transitive dependencies of this package.
+    def possible_dependencies(
+            self, transitive=True, expand_virtuals=True, visited=None):
+        """Return set of possible dependencies of this package.
+
+        Note: the set returned *includes* the package itself.
 
         Args:
-            transitive (bool): include all transitive dependencies if True,
+            transitive (bool): return all transitive dependencies if True,
                 only direct dependencies if False.
+            expand_virtuals (bool): expand virtual dependencies into all
+                possible implementations.
+            visited (set): set of names of dependencies visited so far.
         """
         if visited is None:
-            visited = set()
+            visited = set([self.name])
 
-        visited.add(self.name)
-        for name in self.dependencies:
-            spec = spack.spec.Spec(name)
-
-            if not spec.virtual:
-                visited.add(name)
-                if transitive:
-                    pkg = spack.repo.get(name)
-                    pkg.possible_dependencies(transitive, visited)
+        for i, name in enumerate(self.dependencies):
+            if spack.repo.is_virtual(name):
+                if expand_virtuals:
+                    providers = spack.repo.providers_for(name)
+                    dep_names = [spec.name for spec in providers]
+                else:
+                    visited.add(name)
+                    continue
             else:
-                for provider in spack.repo.providers_for(spec):
-                    visited.add(provider.name)
+                dep_names = [name]
+
+            for dep_name in dep_names:
+                if dep_name not in visited:
+                    visited.add(dep_name)
                     if transitive:
-                        pkg = spack.repo.get(provider.name)
-                        pkg.possible_dependencies(transitive, visited)
+                        pkg = spack.repo.get(dep_name)
+                        pkg.possible_dependencies(
+                            transitive, expand_virtuals, visited)
 
         return visited