[Resolves #937] Reset Jinja2 variable cache between config files

[NathanWilliams]

Fix for: #937

This resets the Jinja2 templating_vars in config/reader.py to prevent variables leaking across StackGroups.

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[ngfgrant]

Thank you @NathanWilliams this has been a really subtle one that is catching folk out.

I think this resolves #813 and #889

I wonder if we could structure a test with this so that we can be sure it fixes the issue?

[NathanWilliams]

@ngfgrant Sure. I have been on a break, so I'll try and fit it in in the next day or so

[alex-harvey-z3q]

@zaro0508 I spent quite a bit of time on this and I believe this is a valid test case:

--- a/tests/test_config_reader.py
+++ b/tests/test_config_reader.py
@@ -621,6 +621,32 @@ class TestConfigReader(object):
 
             assert result == {"key": "value"}
 
+    def test_render__existing_config_file__stack_group_config_leaks(self):
+        with self.runner.isolated_filesystem():
+            project_path = os.path.abspath("./example")
+            config_dir = os.path.join(project_path, "config")
+            directory_path = os.path.join(config_dir, "configs")
+
+            os.makedirs(directory_path)
+
+            basename = "existing_config.yaml"
+            stack_group_config = {}
+
+            test_config_path = os.path.join(directory_path, basename)
+            test_config_content = "key: value\n"
+
+            with open(test_config_path, "w") as file:
+                file.write(test_config_content)
+
+            config_reader = ConfigReader(self.context)
+            config_reader.templating_vars["someone_elses"] = "config"
+            config_reader.templating_vars["stack_group_config"] = {"foo": "bar"}
+            config_reader.templating_vars["var"] = {"baz": "qux"}
+
+            _ = config_reader._render("configs", basename, stack_group_config)
+
+            assert config_reader.templating_vars == {"someone_elses": "config", "stack_group_config": {"foo": "bar"}, "var": {"baz": "qux"}}
+
     def test_render__invalid_jinja_template__raises_and_creates_debug_file(self):
         with self.runner.isolated_filesystem():
             project_path = os.path.abspath("./example")

Where I have failed is to reproduce the original issue in the first place. The original author's set up is quite different to what I'm familiar with and I can't use it to reproduce anything.

I do suspect this bug still exists even 4 years later! If so, we really should merge this.

[alex-harvey-z3q]

I have adopted this stale PR
#1472