Refactor macro contexts. (#36)

* Refactor macro contexts.

* Changelog entry.

.changes/unreleased/Under the Hood-20240122-163546.yaml

@@ -0,0 +1,6 @@
+kind: Under the Hood
+body: Clean up macro contexts.
+time: 2024-01-22T16:35:46.907999-05:00
+custom:
+  Author: peterallenwebb
+  Issue: "35"

dbt_common/clients/jinja.py

@@ -3,9 +3,10 @@
 import os
 import tempfile
 from ast import literal_eval
+from collections import ChainMap
 from contextlib import contextmanager
 from itertools import chain, islice
-from typing import List, Union, Set, Optional, Dict, Any, Iterator, Type, Callable
+from typing import Any, Callable, Dict, Iterator, List, Mapping, Optional, Union, Set, Type
 from typing_extensions import Protocol
 
 import jinja2
@@ -99,6 +100,41 @@ def _compile(self, source, filename):
         return super()._compile(source, filename)  # type: ignore
 
 
+class MacroFuzzTemplate(jinja2.nativetypes.NativeTemplate):
+    environment_class = MacroFuzzEnvironment
+
+    def new_context(
+        self,
+        vars: Optional[Dict[str, Any]] = None,
+        shared: bool = False,
+        locals: Optional[Mapping[str, Any]] = None,
+    ) -> jinja2.runtime.Context:
+        # This custom override makes the assumption that the locals and shared
+        # parameters are not used, so enforce that.
+        if shared or locals:
+            raise Exception("The MacroFuzzTemplate.new_context() override cannot use the shared or locals parameters.")
+
+        parent = ChainMap(vars, self.globals) if self.globals else vars
+
+        return self.environment.context_class(self.environment, parent, self.name, self.blocks)
+
+    def render(self, *args: Any, **kwargs: Any) -> Any:
+        if kwargs or len(args) != 1:
+            raise Exception("The MacroFuzzTemplate.render() override requires exactly one argument.")
+
+        ctx = self.new_context(args[0])
+
+        try:
+            return self.environment_class.concat(  # type: ignore
+                self.root_render_func(ctx)  # type: ignore
+            )
+        except Exception:
+            return self.environment.handle_exception()
+
+
+MacroFuzzEnvironment.template_class = MacroFuzzTemplate
+
+
 class NativeSandboxEnvironment(MacroFuzzEnvironment):
     code_generator_class = jinja2.nativetypes.NativeCodeGenerator
 
@@ -171,7 +207,7 @@ def render(self, *args, **kwargs):
         with :func:`ast.literal_eval`, the parsed value is returned.
         Otherwise, the string is returned.
         """
-        vars = dict(*args, **kwargs)
+        vars = args[0]
 
         try:
             return quoted_native_concat(self.root_render_func(self.new_context(vars)))
@@ -226,7 +262,7 @@ def get_macro(self):
         # make_module is in jinja2.environment. It returns a TemplateModule
         module = template.make_module(vars=self.context, shared=False)
         macro = module.__dict__[get_dbt_macro_name(name)]
-        module.__dict__.update(self.context)
+
         return macro
 
     @contextmanager