test(completion): font completion propagation fixtures

[hongjr03]

Adds font completion fixtures for let/for-loop/record/tuple and imported show transforms. Test-only changes.

Depends on #2388.

[gemini-code-assist]

Summary of Changes

Hello @hongjr03, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the completion capabilities of the language server, particularly for font and path contexts. It introduces sophisticated type propagation logic to understand complex code patterns such as let bindings, destructuring assignments, string concatenations, and dynamic dictionary field access. These improvements ensure that completion suggestions are more accurate and context-aware across a wider range of programming constructs, leading to a better developer experience.

Highlights

• Enhanced Completion Propagation: Improved font and path completion propagation across various language constructs, including let bindings, for loops, record/tuple destructuring, and imported show transforms.
• Robust Constant String Resolution: Introduced new mechanisms to resolve unique constant string values from types and AST nodes, enabling more accurate type checking and completion for dynamic keys and string concatenations.
• Improved Type Inference: Refined contextual type inference for array/dictionary elements and enhanced type variable constraint propagation, leading to more consistent and accurate type information.
• Advanced Path Completion: Path completion now correctly handles string concatenations (e.g., "dir/" + "file.typ") and propagates path types through import and include statements.
• Comprehensive Test Coverage: Added a wide array of new test fixtures and updated snapshots to validate the improved completion and type checking logic across many complex scenarios.

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[gemini-code-assist]

Code Review

This pull request significantly enhances font and path completion by improving type propagation and handling more complex scenarios like string concatenation and dynamic dictionary keys. The changes are well-implemented and backed by a comprehensive set of new tests. The core logic for bi-directional type constraint propagation is a major step forward for the analysis engine. I have one minor suggestion for code simplification.

[gemini-code-assist]

The logic for prepending to the prefix string can be simplified. Instead of creating a new EcoString and reassigning, you can use insert_str to prepend the lhs string directly to the existing prefix. This is more efficient and concise.

Suggested change

	let mut new_prefix = EcoString::new();
	new_prefix.push_str(lhs.as_str());
	new_prefix.push_str(prefix.as_str());
	prefix = new_prefix;
	prefix.insert_str(0, lhs.as_str());