test: add checker for metrics tags (#18927)

Adds a check to verify that the `tags` value passed to metrics calls is
a list of strings, not a dictionary.

Would be better via `mypy`, but the lack of underlying types for Pyramid
makes this much harder, and would need to build out custom stubs.

Refs: #18926

Signed-off-by: Mike Fiedler <miketheman@gmail.com>

Author: miketheman

dev/flake8/checkers.py

@@ -20,6 +20,9 @@
     "over `sqlalchemy.orm.relationship(backref=...)`"
 )
 WH003_msg = "WH003 `@view_config.renderer` configured template file not found"
+# TODO: This would be better served by mypy, no types in Pyramid makes this harder.
+#  Support https://github.com/Pylons/pyramid/issues/2638 for general Pyramid type info.
+WH004_msg = "WH004 metrics tags must be a list of strings"
 
 
 class WarehouseVisitor(ast.NodeVisitor):
@@ -101,6 +104,46 @@ def visit_AnnAssign(self, node: ast.AnnAssign) -> None:  # noqa: N802
         self.check_for_backref(node)
         self.generic_visit(node)
 
+    def is_metrics_method_call(self, node: ast.Call) -> bool:
+        """Check if this is a call to a metrics method."""
+        if not isinstance(node.func, ast.Attribute):
+            return False
+
+        # Check for metrics.<method>()
+        if isinstance(node.func.value, ast.Name) and node.func.value.id == "metrics":
+            return True
+
+        # Check for request.metrics.<method>() or any_obj.metrics.<method>()
+        if (
+            isinstance(node.func.value, ast.Attribute)
+            and node.func.value.attr == "metrics"
+        ):
+            return True
+
+        return False
+
+    def check_metrics_tags(self, node: ast.Call) -> None:
+        """Check that tags parameter in metrics calls is a list."""
+        if not self.is_metrics_method_call(node):
+            return
+
+        # Check keyword arguments for tags=
+        for kw in node.keywords:
+            if kw.arg == "tags":
+                # tags should be None, a variable (Name), or a List
+                # Flag if it's a literal non-list type (string, tuple, dict, set, etc.)
+                if isinstance(kw.value, (ast.Constant, ast.Tuple, ast.Dict, ast.Set)):
+                    # Allow None
+                    if isinstance(kw.value, ast.Constant) and kw.value.value is None:
+                        continue
+                    self.errors.append(
+                        (kw.value.lineno, kw.value.col_offset, WH004_msg)
+                    )
+
+    def visit_Call(self, node: ast.Call) -> None:  # noqa: N802
+        self.check_metrics_tags(node)
+        self.generic_visit(node)
+
     def visit_FunctionDef(self, node: ast.FunctionDef) -> None:  # noqa: N802
         for decorator in node.decorator_list:
             if (
@@ -173,7 +216,45 @@ def my_view(request):
     assert len(visitor.errors) == 0
 
 
+def test_wh004_metrics_tags_invalid_types():
+    # Test case: Invalid tag types (should error)
+    code = dedent(
+        """
+    metrics.increment("counter", tags="string")
+    request.metrics.gauge("gauge", tags=("tuple",))
+    metrics.histogram("hist", tags={"dict": "value"})
+    """
+    )
+    tree = ast.parse(code)
+    visitor = WarehouseVisitor(filename="test_file.py")
+    visitor.visit(tree)
+
+    # Assert that all 3 errors are raised
+    assert len(visitor.errors) == 3
+    assert all(error[2] == WH004_msg for error in visitor.errors)
+
+
+def test_wh004_metrics_tags_valid_types():
+    # Test case: Valid tag types (should not error)
+    code = dedent(
+        """
+    metrics.increment("counter", tags=["tag1", "tag2"])
+    request.metrics.gauge("gauge", tags=None)
+    tag_list = ["tag1"]
+    metrics.histogram("hist", tags=tag_list)
+    """
+    )
+    tree = ast.parse(code)
+    visitor = WarehouseVisitor(filename="test_file.py")
+    visitor.visit(tree)
+
+    # Assert that no errors are raised
+    assert len(visitor.errors) == 0
+
+
 if __name__ == "__main__":
     test_wh003_renderer_template_not_found()
     test_wh003_renderer_template_in_package_path()
-    print("Test passed!")
+    test_wh004_metrics_tags_invalid_types()
+    test_wh004_metrics_tags_valid_types()
+    print("All tests passed!")