Allow nesting values in checksum dicts

A checksum entry such as `{'file': value}` is now interpreted as-if it
was just `value` if the `'file'` matches.
This especially allows `None` values that currently lead to a type error.

easybuild/tools/filetools.py

@@ -1276,6 +1276,9 @@ def verify_checksum(path, checksums, computed_checksums=None):
                 checksum = checksum[filename]
             except KeyError:
                 raise EasyBuildError("Missing checksum for %s in %s", filename, checksum)
+            if not verify_checksum(path, checksum, computed_checksums):
+                return False
+            continue
 
         if isinstance(checksum, string_type):
             # if no checksum type is specified, it is assumed to be MD5 (32 characters) or SHA256 (64 characters)

test/framework/filetools.py

@@ -372,6 +372,8 @@ def test_checksums(self):
         # Check dictionary
         alt_checksums = (known_checksums['sha256'],)
         self.assertTrue(ft.verify_checksum(fp, {os.path.basename(fp): known_checksums['sha256']}))
+        # None is accepted
+        self.assertTrue(ft.verify_checksum(fp, {os.path.basename(fp): None}))
         faulty_dict = {'wrong-name': known_checksums['sha256']}
         self.assertErrorRegex(EasyBuildError,
                               "Missing checksum for " + os.path.basename(fp) + " in .*wrong-name.*",
@@ -388,6 +390,8 @@ def test_checksums(self):
         self.assertTrue(ft.verify_checksum(fp, known_checksums['sha256']))
 
         # Test dictionary-type checksums
+        self.assertErrorRegex(EasyBuildError, "Missing checksum for", ft.verify_checksum,
+                              fp, {os.path.basename(fp): None})
         for checksum in [known_checksums[x] for x in ('md5', 'sha256')]:
             dict_checksum = {os.path.basename(fp): checksum, 'foo': 'baa'}
             self.assertTrue(ft.verify_checksum(fp, dict_checksum))