fix: merge pseudo-parameters in sam_template_validator before expansion

expand_language_extensions was called with only self.parameter_overrides,
missing pseudo-parameters (AWS::Region, AWS::AccountId, etc.). Every
other caller merges IntrinsicsSymbolTable.DEFAULT_PSEUDO_PARAM_VALUES
first. Without pseudo-params, templates using Ref: AWS::Region in
Fn::ForEach collections or Fn::Sub expressions would fail during
sam validate but work correctly with sam build and sam package.

Author: bnusunny

samcli/lib/translate/sam_template_validator.py

@@ -15,6 +15,7 @@
 from samcli.commands.validate.lib.exceptions import InvalidSamDocumentException
 from samcli.lib.cfn_language_extensions.sam_integration import expand_language_extensions
 from samcli.lib.cfn_language_extensions.utils import is_foreach_key
+from samcli.lib.intrinsic_resolver.intrinsics_symbol_table import IntrinsicsSymbolTable
 from samcli.lib.utils.packagetype import IMAGE, ZIP
 from samcli.lib.utils.resources import AWS_SERVERLESS_FUNCTION
 from samcli.yamlhelper import yaml_dump
@@ -87,7 +88,9 @@ def get_translated_template_if_valid(self):
         )
 
         # Process language extensions before validation if AWS::LanguageExtensions transform is present
-        result = expand_language_extensions(self.sam_template, parameter_values=self.parameter_overrides)
+        parameter_values = dict(IntrinsicsSymbolTable.DEFAULT_PSEUDO_PARAM_VALUES)
+        parameter_values.update(self.parameter_overrides)
+        result = expand_language_extensions(self.sam_template, parameter_values=parameter_values)
         if result.had_language_extensions:
             self.sam_template = result.expanded_template