fix: narrow exception handling and bound expansion cache size

- artifact_exporter.py: catch InvalidSamDocumentException instead of bare
  Exception so programming bugs propagate instead of being silently swallowed
- sam_integration.py: add _MAX_CACHE_SIZE=32 with FIFO eviction to prevent
  unbounded memory growth in long-running processes (sam sync --watch)

Author: bnusunny

samcli/lib/cfn_language_extensions/sam_integration.py

@@ -37,6 +37,7 @@
 # Module-level cache for expand_language_extensions() results.
 # Key: (template_path, file_mtime, parameter_values_hash)
 _expansion_cache: Dict[Tuple[str, float, str], "LanguageExtensionResult"] = {}
+_MAX_CACHE_SIZE = 32
 
 
 def _hash_params(parameter_values: Optional[Dict[str, Any]]) -> str:
@@ -61,6 +62,13 @@ def clear_expansion_cache() -> None:
     _expansion_cache.clear()
 
 
+def _cache_put(key: Tuple[str, float, str], value: "LanguageExtensionResult") -> None:
+    """Store a result in the expansion cache, evicting the oldest entry if full."""
+    if len(_expansion_cache) >= _MAX_CACHE_SIZE:
+        _expansion_cache.pop(next(iter(_expansion_cache)))
+    _expansion_cache[key] = value
+
+
 @dataclass(frozen=True)
 class LanguageExtensionResult:
     """
@@ -560,12 +568,12 @@ def expand_language_extensions(
         )
         if cache_key is not None:
             # Store a deep copy so callers can't poison the cache
-            _expansion_cache[cache_key] = LanguageExtensionResult(
+            _cache_put(cache_key, LanguageExtensionResult(
                 expanded_template=copy.deepcopy(result.expanded_template),
                 original_template=copy.deepcopy(result.original_template),
                 dynamic_artifact_properties=list(result.dynamic_artifact_properties),
                 had_language_extensions=result.had_language_extensions,
-            )
+            ))
         return result
 
     LOG.debug("Expanding CloudFormation Language Extensions (Phase 1)")
@@ -601,12 +609,12 @@ def expand_language_extensions(
 
         if cache_key is not None:
             # Store a deep copy so callers can't poison the cache
-            _expansion_cache[cache_key] = LanguageExtensionResult(
+            _cache_put(cache_key, LanguageExtensionResult(
                 expanded_template=copy.deepcopy(result.expanded_template),
                 original_template=copy.deepcopy(result.original_template),
                 dynamic_artifact_properties=list(result.dynamic_artifact_properties),
                 had_language_extensions=result.had_language_extensions,
-            )
+            ))
 
         return result
 

samcli/lib/package/artifact_exporter.py

@@ -22,6 +22,7 @@
 
 from samcli.commands._utils.experimental import ExperimentalFlag, is_experimental_enabled
 from samcli.commands.package import exceptions
+from samcli.commands.validate.lib.exceptions import InvalidSamDocumentException
 from samcli.lib.cfn_language_extensions.utils import iter_regular_resources
 from samcli.lib.package.code_signer import CodeSigner
 from samcli.lib.package.local_files_utils import get_uploaded_s3_object_name, mktempfile
@@ -107,7 +108,7 @@ def do_export(self, resource_id, resource_dict, parent_dir):
 
         try:
             result = expand_language_extensions(child_template_dict, parameter_values, template_path=abs_template_path)
-        except Exception:
+        except InvalidSamDocumentException:
             LOG.debug("Language extensions expansion failed for %s, using original template", abs_template_path)
             result = None