Fix spack graph when deptypes are filtered (#22121)

var/spack/repos/builtin.mock/packages/both-link-and-build-dep-a/package.py

@@ -0,0 +1,24 @@
+# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class BothLinkAndBuildDepA(Package):
+    """
+        Structure where c occurs as a build dep down the line and as a direct
+        link dep. Useful for testing situations where you copy the parent spec
+        just with link deps, and you want to make sure b is not part of that.
+        a <--build-- b <-link-- c
+        a <--link--- c
+    """
+
+    homepage = "http://www.example.com"
+    url      = "http://www.example.com/1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    depends_on('both-link-and-build-dep-b', type='build')
+    depends_on('both-link-and-build-dep-c', type='link')

var/spack/repos/builtin.mock/packages/both-link-and-build-dep-b/package.py

@@ -0,0 +1,23 @@
+# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class BothLinkAndBuildDepB(Package):
+    """
+        Structure where c occurs as a build dep down the line and as a direct
+        link dep. Useful for testing situations where you copy the parent spec
+        just with link deps, and you want to make sure b is not part of that.
+        a <--build-- b <-link-- c
+        a <--link--- c
+    """
+
+    homepage = "http://www.example.com"
+    url      = "http://www.example.com/1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    depends_on('both-link-and-build-dep-c', type='link')

var/spack/repos/builtin.mock/packages/both-link-and-build-dep-c/package.py

@@ -0,0 +1,21 @@
+# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class BothLinkAndBuildDepC(Package):
+    """
+        Structure where c occurs as a build dep down the line and as a direct
+        link dep. Useful for testing situations where you copy the parent spec
+        just with link deps, and you want to make sure b is not part of that.
+        a <--build-- b <-link-- c
+        a <--link--- c
+    """
+
+    homepage = "http://www.example.com"
+    url      = "http://www.example.com/1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')