Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

When the regex alternation tries to match scalar AWSDateTime, it matches scalar AWSDate first (because AWSDate appears before AWSDateTime in the list), removes it, and leaves Time behind causing the syntax error and AppSync deployment to fail.

Expected Behavior

The schema should parse correctly.

How are you starting LocalStack?

With the localstack script

Steps To Reproduce

How are you starting localstack (e.g., bin/localstack command, arguments, or docker-compose.yml)

localstack start

Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

cdklocal deploy --all

Environment

- OS: MacOS 26.1
- LocalStack: Pro
  LocalStack version: 4.10.1.dev41
  LocalStack Docker image sha: f71fee9f3a3f
  LocalStack build date: 2025-11-19
  LocalStack build git hash: 252071cd1

Anything else?

Summary

LocalStack's AppSync provider fails to parse GraphQL schemas containing scalar AWSDateTime with the error:

Syntax Error: Unexpected Name 'Time'.
GraphQL request:38:1
39 | Time

Full Disclosure

I performed an exec into the localstack-main container and figured out how to decrypt the Python files so I could debug this and discover the root cause.

Root Cause

In localstack/pro/core/services/appsync/graphql_executor.py, line 136, the regex used to remove AWS scalar type definitions has a bug:

AWS_SCALAR_TYPES=['AWSDate','AWSTime','AWSDateTime','AWSTimestamp','AWSEmail','AWSJSON','AWSURL','AWSPhone','AWSIPAddress']
AWS_SCALAR_REGEX=f"scalar\\s+(?:{"|".join(AWS_SCALAR_TYPES)})"

# Line 136:
A=re.sub(AWS_SCALAR_REGEX,'',A)

The Problem: When the regex alternation tries to match scalar AWSDateTime, it matches scalar AWSDate first (because AWSDate appears before AWSDateTime in the list), removes it, and leaves Time behind.

Example

Input schema:

scalar AWSDateTime

After regex substitution:

Time

This causes GraphQL to fail parsing with "Unexpected Name 'Time'".

Fix Options

Option 1: Sort by length (longest first)

AWS_SCALAR_REGEX = r"scalar\s+(?:" + "|".join(sorted(AWS_SCALAR_TYPES, key=len, reverse=True)) + ")"

Option 2: Add word boundary

AWS_SCALAR_REGEX = r"scalar\s+(?:" + "|".join(AWS_SCALAR_TYPES) + r")\b"

Both fixes ensure that longer type names like AWSDateTime are matched completely before shorter ones like AWSDate.

Reproduction

1. Create a GraphQL schema with scalar AWSDateTime
2. Deploy to LocalStack using CDK or CloudFormation
3. Observe the error: Syntax Error: Unexpected Name 'Time'

Verification

import re

AWS_SCALAR_TYPES=['AWSDate','AWSTime','AWSDateTime','AWSTimestamp','AWSEmail','AWSJSON','AWSURL','AWSPhone','AWSIPAddress']

# Buggy regex
AWS_SCALAR_REGEX_BUGGY = r"scalar\s+(?:" + "|".join(AWS_SCALAR_TYPES) + ")"
test = "scalar AWSDateTime"
print(re.sub(AWS_SCALAR_REGEX_BUGGY, '', test))  # Output: "Time" 

# Fixed regex (with word boundary)
AWS_SCALAR_REGEX_FIXED = r"scalar\s+(?:" + "|".join(AWS_SCALAR_TYPES) + r")\b"
print(re.sub(AWS_SCALAR_REGEX_FIXED, '', test))  # Output: ""