Implement message template syntax deprecation and migration

[david-waltermire]

Summary

Implement the deprecation of single-brace { expr } message template syntax in favor of mustache-style {{ expr }} syntax, as specified in metaschema-framework/metaschema#162.

Implementation Areas

1. Message Template Parser

Location: core/src/main/java/gov/nist/secauto/metaschema/core/model/constraint/impl/ (or similar)

• Update parser to handle chosen transition approach (see Deprecate single-brace message template syntax in favor of mustache-style double-braces metaschema#162 for options)
• Implement deprecation detection for legacy { expr } syntax
• Add support for new {{ expr }} syntax

2. Deprecation Warning System

• Track warned files to emit ONE warning per file (avoid log spam)
• Warning format: WARNING: File '{}' uses deprecated single-brace template syntax. Use '{{ expr }}' instead of '{ expr }'.
• Consider adding source location (line/column) for the first occurrence

// Example implementation
private static final Set<URI> warnedFiles = ConcurrentHashMap.newKeySet();

private void warnDeprecatedSyntax(URI sourceFile) {
  if (warnedFiles.add(sourceFile)) {
    LOGGER.warn("File '{}' uses deprecated single-brace template syntax. "
        + "Use '{{ expr }}' instead of '{ expr }'.", sourceFile);
  }
}

3. CLI Migration Command

Location: metaschema-cli

Add a new command to migrate constraint files:

# Dry-run showing what would change
metaschema-cli migrate-templates --dry-run constraints.xml

# Apply changes in place
metaschema-cli migrate-templates constraints.xml

# Output to different file
metaschema-cli migrate-templates constraints.xml -o constraints-v2.xml

# Report mode - list files using deprecated syntax
metaschema-cli migrate-templates --report src/

4. Validation Mode

Add CLI flag or configuration option to treat deprecated syntax as an error:

metaschema-cli validate --strict-templates module.xml

This enables CI pipelines to enforce migration.

Dependencies

• Requires decision on transition approach in Deprecate single-brace message template syntax in favor of mustache-style double-braces metaschema#162
• Parser changes depend on which option is selected (file-level marker, hard cutover, etc.)

Acceptance Criteria

• Parser updated per chosen transition approach
• Deprecation warnings emitted (one per file)
• migrate-templates CLI command implemented
• --dry-run and --report modes working
• --strict-templates validation flag implemented
• Unit tests for parser with both syntaxes
• Integration tests for CLI migration command
• Documentation updated

Related

• Deprecate single-brace message template syntax in favor of mustache-style double-braces metaschema#162 - Specification and transition approach decision
• fix: correct message template syntax in module constraints metaschema#161 - Fix message template syntax in module constraints

[coderabbitai]

📝 CodeRabbit Plan Mode

Generate an implementation plan and prompts that you can use with your favorite coding agent.

• Create Plan

Examples

• Example 1
• Example 2

---

🔗 Similar Issues

Possible Duplicates

• Deprecate single-brace message template syntax in favor of mustache-style double-braces metaschema#162

Related Issues

• Support message syntax and semantics to all constraint types metaschema#34
• Refactor to Native Metaschema API Implementation oscal-server#32
• Support custom constraint messages for non-expect constraints #215
• Enhance validate command to perform Metaschema and constraint-based validation of modules  #231

🔗 Related PRs

#137 - Ensure SARIF results are valid to SARIF JSON schema [merged]
#290 - Feature/289 improve message errors [merged]
metaschema-framework/metaschema#161 - fix: correct message template syntax in module constraints [closed]

👤 Suggested Assignees

• david-waltermire
• aj-stein-gsa
• wandmagic

---

🧪 Issue enrichment is currently in open beta.

You can configure auto-planning by selecting labels in the issue_enrichment configuration.

To disable automatic issue enrichment, add the following to your .coderabbit.yaml:

issue_enrichment:
  auto_enrich:
    enabled: false

💬 Have feedback or questions? Drop into our discord!