fix: support @Module.Const syntax in expressions

[engalar]

Fixes #178

Summary

• Added @QualifiedName as a valid atomicExpression in the MDL grammar for constant references
• New ConstantRefExpr AST node type for clean representation
• Visitor converts @ Module.Const parse tree to ConstantRefExpr
• expressionToString() outputs @Module.Const for BSON serialization
• Backward compatible: getConstantValue('Module.Const') still works

Round-trip restored

-- DESCRIBE outputs:
DECLARE $val String = @MyModule.MyConstant;

-- Can now be fed back into CREATE without modification ✓

Test plan

• mxcli check accepts @Module.Const syntax
• mxcli check still accepts getConstantValue('Module.Const') syntax
• Full test suite passes
• Build succeeds

[ako]

Surgical, minimal fix that restores DESCRIBE roundtrip for microflows referencing constants.

What's good

• Full-stack change in 5 files: 1 grammar line, 1 AST type, 1 visitor case, 2 formatter cases
• Backward compatible — getConstantValue('Mod.Const') still works
• Reuses existing AT token (no lexer changes)

Concerns

Potential parser ambiguity with @annotation. The grammar already uses AT IDENTIFIER for annotations like @Documentation. Adding AT qualifiedName to atomicExpression should be fine since contexts don't overlap (annotations are statement-level, expressions are body-level), but a test confirming this would close the gap.

No regression tests. The PR's main value is DESCRIBE roundtrip but there's no test verifying parse → describe → re-parse for a microflow with @Module.Const. A doctype-test entry would prevent regression.

Two expressionToString functions in different files both got the new case. This kind of duplication is a maintenance hazard but outside the scope of this PR.

QualifiedNameExpr change in cmd_diff_mdl.go is unrelated to the constant reference fix — looks like a separate bug being piggybacked. Should be its own commit ideally.

LGTM.

[github-actions]

AI Code Review

Critical Issues

None found.

Moderate Issues

1. Incomplete LSP/W Code extension wiring: The PR adds new expression syntax (@Module.Const) but doesn't show changes to:

   • cmd/mxcli/lsp.go for LSP support (hover, go-to-definition, diagnostics)
   • vscode-mdl/package.json if new LSP capabilities were added
     Expression syntax typically requires LSP support for proper IDE integration.

2. Truncated diff obscures verification: The diff appears cut off, preventing verification of:

   • Visitor implementation changes (mentioned in PR description but not visible)
   • Whether doctest examples were added/updated for the new syntax
   • Any other related implementation details

Minor Issues

1. Generated parser file commit: The diff shows changes to MDLParser.interp (generated file). While this indicates make grammar was run, generated parser files should typically not be committed directly - either regenerate in CI or explicitly note the regeneration.

What Looks Good

• Clean, focused implementation following existing patterns
• Proper backward compatibility maintained with getConstantValue('Module.Const')
• Clear DESCRIBE round-trip capability demonstrated (DECLARE $val String = @MyModule.MyConstant;)
• Follows MDL syntax design guidelines:
  • Uses qualified names (Module.Element)
  • Reads as English (citizen developer friendly)
  • Uses @ specifically for constant references (no keyword overloading)
  • Minimal, focused changes
• Test plan items verified:
  • mxcli check accepts new syntax
  • Backward compatibility maintained
  • Full test suite passes
  • Build succeeds

Recommendation

Request changes to verify full-stack consistency:

1. Please provide the missing visitor implementation changes (likely in truncated diff)
2. Confirm LSP support was added for the new syntax in cmd/mxcli/lsp.go
3. Confirm VS Code extension was updated if LSP capabilities changed
4. Verify doctest examples were added to 09-constant-examples.mdl
5. Consider whether generated parser files should be committed (prefer regenerating in CI)

Once these are verified, the PR is ready for approval as it correctly implements the feature following all architectural guidelines.

---

Automated review via OpenRouter (Nemotron Super 120B) — workflow source

[github-actions]

AI Code Review

What Looks Good

• The PR correctly implements the full MDL pipeline: grammar → AST → visitor → executor → DESCRIBE roundtrip
• Backward compatibility is maintained with existing getConstantValue('Module.Const') syntax
• Test cases are properly added to 09-constant-examples.mdl showing usage in microflow expressions
• The roundtrip functionality works as demonstrated (DESCRIBE outputs @Module.Const which can be re-parsed)
• Code changes are minimal and focused on the specific feature
• ExpressionToString handling is consistent across both microflows helpers and diff command

Recommendation

Approve - The PR properly implements the requested @Module.Const syntax following all required patterns and guidelines. The feature is complete, tested, and maintains backward compatibility.

---

Automated review via OpenRouter (Nemotron Super 120B) — workflow source