Package hashing: fix detection of directives (#14763)

The hashing logic looks for function calls that are Spack directives.
It expects that when a Spack directive is used that it is referenced
directly by name, and that the directive function is not itself
retrieved by calling another function. When the hashing logic
encountered a function call where the function was determined
dynamically, it would fail (attempting to access a name attribute
that does not happen to exist in this case).

This updates the hashing logic to filter out function calls where the
function is determined dynamically when looking for uses of Spack
directives.

lib/spack/spack/test/packages.py

@@ -98,6 +98,10 @@ def test_all_same_but_archive_hash(self):
         assert spec1.package.content_hash(content=content1) != \
             spec2.package.content_hash(content=content2)
 
+    def test_parse_dynamic_function_call(self):
+        spec = Spec("hash-test4").concretized()
+        spec.package.content_hash()
+
     # Below tests target direct imports of spack packages from the
     # spack.pkg namespace
     def test_import_package(self):

lib/spack/spack/util/package_hash.py

@@ -41,8 +41,23 @@ def __init__(self, spec):
         self.spec = spec
 
     def is_directive(self, node):
+        """Check to determine if the node is a valid directive
+
+        Directives are assumed to be represented in the AST as a named function
+        call expression.  This means that they will NOT be represented by a
+        named function call within a function call expression (e.g., as
+        callbacks are sometimes represented).
+
+        Args:
+            node (AST): the AST node being checked
+
+        Returns:
+            (bool): ``True`` if the node represents a known directive,
+                ``False`` otherwise
+        """
         return (isinstance(node, ast.Expr) and
                 node.value and isinstance(node.value, ast.Call) and
+                isinstance(node.value.func, ast.Name) and
                 node.value.func.id in spack.directives.__all__)
 
     def is_spack_attr(self, node):

var/spack/repos/builtin.mock/packages/hash-test4/package.py

@@ -0,0 +1,27 @@
+# Copyright 2013-2020 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 HashTest4(Package):
+    """This package isn't compared with others, but it contains constructs
+       that package hashing logic has tripped over in the past.
+    """
+
+    homepage = "http://www.hashtest4.org"
+    url = "http://www.hashtest1.org/downloads/hashtest4-1.1.tar.bz2"
+
+    version('1.1', 'a' * 32)
+
+    def install(self, spec, prefix):
+        pass
+
+    @staticmethod
+    def examine_prefix(pkg):
+        pass
+
+    run_after('install')(
+        examine_prefix)