72 feature error type poisoning

[CMI-James]

Description

Closes #72

Changes proposed

What were you told to do?

I was tasked with implementing Error Type Poisoning to prevent cascading errors in the type checker. This involved adding a TypeInfoKind::Error variant similar to rustc's TyKind::Error and updating the type checker to gracefully handle these error types.

What did I do?

Implemented TypeInfoKind::Error

• Added Error variant to the TypeInfoKind enum in core/type-checker/src/type_info.rs.
• Updated Display implementation to show {unknown} for error types.
• Added is_error() helper method to TypeInfo.
• Updated substitute and has_unresolved_params to handle Error variants neutrally.

Updated Type Checker Logic

• Modified core/type-checker/src/type_checker.rs to use TypeInfoKind::Error for type poisoning.
• Updated infer_expression for Identifier, Struct initialization, MemberAccess, TypeMemberAccess, and FunctionCall to return TypeInfoKind::Error upon lookup failure instead of None or continuing with invalid types.
• Updated type mismatch checks in Statement::Assign, Statement::Return, Statement::If, Statement::Loop, and others to suppress errors if either the expected or found type is Error.
• Updated Expression::ArrayIndexAccess, Expression::PrefixUnary, and Expression::Binary to propagate Error types and suppress secondary errors (e.g., "expected array type" when the array expression itself failed).

Added Tests

• Created tests/src/type_checker/error_type_poisoning_tests.rs with comprehensive tests covering:
  • TypeInfoKind::Error variant behavior (is_error(), Display, substitute, has_unresolved_params)
  • Cascading error suppression (undeclared variables, undefined structs, undefined functions, binary/unary operations, conditions)
  • Error propagation through assignments, struct initialization, chained member access, method calls, function arguments
  • Error types in complex expressions (nested binary, array literals, conditionals, assertions)
  • Error type equality

Benefits

• Prevents cascading errors when a type lookup fails.
• Allows type checking to continue more gracefully.
• Aligns with rustc's error handling model.

AI Disclosure

AI tools (Claude) were used to assist with the following parts of this implementation:

AI-generated code (reviewed and tested before submission):

• core/type-checker/src/type_info.rs: Added TypeInfoKind::Error variant, is_error() method, Display match arm for Error, and handling in substitute/has_unresolved_params
• core/type-checker/src/type_checker.rs: Updated type mismatch checks to skip errors when either type is Error, modified infer_expression branches to return TypeInfoKind::Error on lookup failures
• tests/src/type_checker/error_type_poisoning_tests.rs: AI assisted with test structure and test case implementation

Human contributions:

• Overall design decision to use rustc-style error poisoning
• Review and validation of all generated code
• Testing the implementation against the existing test suite

Check List (Check all the applicable boxes)

🚨Please review the contribution guideline for this repository.

• My code follows the code style of this project.
• This PR does not contain plagiarized content.
• The title and description of the PR is clear and explains the approach.
• I am making a pull request against the main branch (left side).
• My commit messages styles matches our requested structure.
• My code additions will fail neither code linting checks nor unit test.
• I am only making changes to files I was requested to.

Screenshots/Videos

[SurfingBowser]

As pointed out in the contributor guide

State clearly in the PR description which parts of the code were generated by AI tools

[CMI-James]

@SurfingBowser updated.