Avoid processing the same EasyConfig multiple times

When passing the same EasyConfig file multiple times on the commandline
it will be parsed once and put into a cache.
Every future call will get the same `EasyConfig` instance so any
modification to it will be reflected in all future uses of supposedly
"freshly parsed EasyConfigs".
This leads to confusing failures when trying to build the same file twice
which is likely a mistake anyway, especially when one file is a symlink
to another one passed too.
So just make sure each physical file is parsed only once.

Author: Flamefire

easybuild/framework/easyconfig/tools.py

@@ -404,9 +404,15 @@ def parse_easyconfigs(paths, validate=True):
     """
     easyconfigs = []
     generated_ecs = False
+    parsed_paths = []
 
     for (path, generated) in paths:
+        # Avoid processing the same file multiple times
         path = os.path.abspath(path)
+        if any(os.path.samefile(path, p) for p in parsed_paths):
+            continue
+        parsed_paths.append(path)
+
         # keep track of whether any files were generated
         generated_ecs |= generated
         if not os.path.exists(path):

test/framework/easyconfig.py

@@ -737,6 +737,32 @@ def test_tweaking(self):
         # cleanup
         os.remove(tweaked_fn)
 
+    def test_parse_easyconfig(self):
+        """Test parse_easyconfig function"""
+        self.contents = textwrap.dedent("""
+            easyblock = "ConfigureMake"
+            name = "PI"
+            version = "3.14"
+            homepage = "http://example.com"
+            description = "test easyconfig"
+            toolchain = SYSTEM
+        """)
+        self.prep()
+        ecs, gen_ecs = parse_easyconfigs([(self.eb_file, False)])
+        self.assertEqual(len(ecs), 1)
+        self.assertEqual(ecs[0]['spec'], self.eb_file)
+        self.assertIsInstance(ecs[0]['ec'], EasyConfig)
+        self.assertFalse(gen_ecs)
+        # Passing the same EC multiple times is ignored
+        ecs, gen_ecs = parse_easyconfigs([(self.eb_file, False), (self.eb_file, False)])
+        self.assertEqual(len(ecs), 1)
+        # Similar for symlinks
+        linked_ec = os.path.join(self.test_prefix, 'linked.eb')
+        os.symlink(self.eb_file, linked_ec)
+        ecs, gen_ecs = parse_easyconfigs([(self.eb_file, False), (linked_ec, False)])
+        self.assertEqual(len(ecs), 1)
+        self.assertEqual(ecs[0]['spec'], self.eb_file)
+
     def test_alt_easyconfig_paths(self):
         """Test alt_easyconfig_paths function that collects list of additional paths for easyconfig files."""