Hassfest check for invalid localization placeholders (#155216)

script/hassfest/translations.py

@@ -5,6 +5,7 @@ from __future__ import annotations
 from functools import partial
 import json
 import re
+import string
 from typing import Any
 
 import voluptuous as vol
@@ -131,10 +132,12 @@ def translation_value_validator(value: Any) -> str:
 
     - prevents string with HTML
     - prevents strings with single quoted placeholders
+    - prevents strings with placeholders using invalid identifiers
     - prevents combined translations
     """
     string_value = cv.string_with_no_html(value)
     string_value = string_no_single_quoted_placeholders(string_value)
+    string_value = validate_placeholders(string_value)
     if RE_COMBINED_REFERENCE.search(string_value):
         raise vol.Invalid("the string should not contain combined translations")
     if string_value != string_value.strip():
@@ -151,6 +154,19 @@ def string_no_single_quoted_placeholders(value: str) -> str:
     return value
 
 
+def validate_placeholders(value: str) -> str:
+    """Validate that placeholders in translations use valid identifiers."""
+    formatter = string.Formatter()
+
+    for _, field_name, _, _ in formatter.parse(value):
+        if field_name:  # skip literal text segments
+            if not field_name.isidentifier():
+                raise vol.Invalid(
+                    "placeholders must be valid identifiers ([a-zA-Z_][a-zA-Z0-9_]*)"
+                )
+    return value
+
+
 def gen_data_entry_schema(
     *,
     config: Config,