Aaron Pollack

This commit **adds a new blog post** to the **Pyrefly website's blog section**, specifically the file `website/blog/2026-04-01-100-percent-type-coverage.md`. This **new content** provides an article titled 'Reaching 100% Type Coverage by Deleting Unannotated Code', which explores a novel approach to achieving full type coverage in Python codebases. This **documentation** update expands the project's public-facing educational resources, offering insights into a specific development practice.

This commit **enhances the error reporting system** within `pyrefly` by intelligently displaying secondary annotations. It introduces a **new behavior** where annotations more than 10 lines away from the primary error span are presented as distinct snippets, preventing excessive irrelevant context in the output. Concurrently, the `MAX_LINES` constant for inline snippets is increased from 5 to 10, improving readability for typical function bodies. This **refactoring of snippet generation** in `pyrefly/lib/error/error.rs` (affecting functions like `get_source_snippet`) significantly **improves the clarity and conciseness of error messages** for developers.

This commit **adds new test cases** to the `pyrefly` project, specifically targeting **edge cases in assignment unpacking and slicing operations**. It introduces tests for scenarios where string literals are unpacked with too many or too few target variables, such as `a, b = "abc"` or `a, b = "x"`, and for slicing with a zero step size. These **new tests**, located in `pyrefly/lib/test/assign.rs`, are a **maintenance** effort aimed at **detecting existing bugs** and improving the **robustness and correctness** of the interpreter's handling of these fundamental language features. Their inclusion will help ensure the `pyrefly` interpreter behaves as expected in these previously undetected error conditions.

This commit introduces a **new capability** to significantly **enhance operator error diagnostics** within the **type checking system**. It now provides **secondary type annotations** for binary, inplace binary, and unary operator type mismatches, clearly labeling each operand with its inferred type directly in the error message. This is achieved by adding an `annotations` field to `TypeCheckContext` and updating the `add_with_annotations` function in the error collector to merge these new annotations. This improvement makes type-related errors more informative and actionable for developers, particularly when debugging type mismatches in expressions.

This commit introduces a **new capability** to **enhance error diagnostics** for function call argument type mismatches within the **type checking subsystem**. It modifies the inference process to thread `callee_range` through functions like `call_infer_inner` and `callable_infer_params`, enabling the system to add a secondary "function defined here" annotation to relevant error messages. This involves updates to `pyrefly/lib/alt/call.rs`, `pyrefly/lib/alt/callable.rs`, and the addition of a `with_callee_annotation` method in `pyrefly/lib/error/context.rs`. The **downstream impact** is clearer and more actionable error messages for developers, making it easier to identify the definition of the called function directly at the call site when an argument type mismatch occurs.

This commit introduces a **diagnostic enhancement** to the **type checker** within the `pyrefly` library, specifically targeting **function parameter analysis**. It **improves error messages** for situations where a function parameter's default value does not match its declared type. The updated diagnostics now include a secondary label that points directly to the **declared type annotation** in the source code, providing clearer context for the mismatch. This **feature enhancement**, primarily affecting `pyrefly/lib/alt/function.rs`, makes **type-checking errors more actionable** and easier for developers to understand and resolve.

This commit significantly **improves error diagnostics** within the **PyRefly type checker** by adding secondary annotations to **return type and annotated assignment errors**. Specifically, it now explicitly labels the *declared type* in these error messages, making it clearer to developers which type annotation is being violated. This **new capability**, primarily implemented in `pyrefly/lib/alt/solve.rs` to extract annotation ranges and supported by a new `with_annotation` helper in `pyrefly/lib/error/context.rs`, enhances the **developer experience** by providing more precise and actionable feedback for type mismatches.

This commit introduces **new tests** to the `pyrefly/lib/test/dataclasses.rs` module, specifically targeting **restrictions on `@dataclass` usage**. It adds five test cases to verify that applying `@dataclass` to `NamedTuple`, `TypedDict`, `Enum`, and `Protocol` correctly raises errors, and that overriding `__setattr__` or `__delattr__` in a `frozen` dataclass is also properly flagged. This **maintenance** work improves the **quality assurance** of the **dataclass implementation** by detecting previously uncaught bugs and ensuring its robust behavior against invalid class definitions. The added tests help prevent regressions and enforce correct usage patterns for this core feature.

This commit **enhances the test suite** for the **`pyrefly` runtime** by introducing two new test cases in `pyrefly/lib/test/slots.rs`. These tests are designed to expose **`__slots__` layout conflicts** that occur in **multiple inheritance scenarios**, specifically addressing issues where `__slots__` definitions conflict or share identical names across different base classes. This **testing enhancement** aims to identify currently undetected bugs in `pyrefly`'s object model, ensuring robust and correct behavior when handling complex inheritance patterns with `__slots__`. The addition of these tests is a critical step towards improving the overall stability and correctness of the `pyrefly` system.

This commit **adds new test cases** to the `pyrefly` library, specifically targeting **call expression evaluation** edge cases. It introduces two tests: one to ensure that `NotImplemented()` is correctly identified as non-callable, and another to verify that instances with a non-callable `__call__` attribute (e.g., `__call__ = 42`) are also treated as non-callable. This **testing** work improves the robustness of the interpreter's call handling by proactively identifying potential bugs related to invoking non-callable objects. The new tests are located in `pyrefly/lib/test/calls.rs`.

This commit **enhances the test suite** for the **Python protocol implementation** within the `pyrefly` library. It introduces two new test cases in `pyrefly/lib/test/protocol.rs` to address specific **edge cases** in protocol behavior. The tests, `test_protocol_isinstance_non_method_members` and `test_protocol_ambiguous_member`, validate `issubclass` functionality with `runtime_checkable` data protocols and probe for issues with unannotated assignments in protocol bodies. This **testing enhancement** improves the **robustness and correctness** of the protocol type checking system by expanding coverage for complex and potentially problematic scenarios.

This commit **adds a new test case** to the `pyrefly/lib` module, specifically within `test/named_tuple.rs`. The test is designed to verify that the **`NamedTuple` implementation** correctly prevents users from **overriding its reserved methods**, such as `_asdict` and `_make`. This is a **test addition** that highlights a currently undetected **bug** or missing validation, ensuring that attempts to modify these critical internal methods will result in an error. By enforcing this restriction, the commit helps maintain the **stability and predictability** of `NamedTuple` behavior across the system.

This commit **enhances the testing suite** for the **Method Resolution Order (MRO)** and **metaclass conflict detection** within the `pyrefly` library. It introduces three new test cases in `pyrefly/lib/test/mro.rs` to validate behavior for duplicate base classes (e.g., `class Bad(A, A)`), duplicate protocol base classes (noting an existing undetected bug), and conflicting metaclasses in multiple inheritance. This **maintenance** work improves **test coverage** for complex inheritance scenarios, aiding in the identification and future resolution of subtle type system bugs.

This commit performs **test cleanup** by **removing three duplicate test cases** from the **Method Resolution Order (MRO)** and **Protocol implementation** test suites. Specifically, `test_duplicate_base_class` and `test_conflicting_metaclass` were removed from `mro.rs` as their coverage was already provided by tests in `dataclasses.rs` and `class_keywords.rs` respectively. Additionally, `test_protocol_isinstance_non_method_members` was removed from `protocol.rs` due to redundancy with `test_protocol_data_protocol_issubclass` in the same file. This **maintenance** effort streamlines the test suite, improving its efficiency and maintainability without affecting the core functionality of MRO or Protocols.

This commit **enhances the test suite** for the **`pyrefly`** project by **adding new test cases** for various **operator edge cases**. These tests cover scenarios such as division by zero, unary and binary operations on class objects, unsupported augmented assignments, and `__bool__` conversion issues, some of which highlight **currently undetected bugs**. This **maintenance and testing improvement** aims to bolster the **correctness and reliability** of the interpreter's **runtime operator handling**, ensuring proper error detection and behavior in unusual or erroneous situations.

This commit **adds a new test case** to the `pyrefly` library's **control flow analysis** suite, specifically within `pyrefly/lib/test/flow_looping.rs`. The new test, `test_possibly_unresolved_after_loop`, verifies that the analyzer correctly identifies variables that may be **unbound after a loop** if their definition is conditional or exclusively within the loop's body. This **enhances the robustness** of the static analysis by ensuring proper handling of variable resolution in complex looping constructs. The addition improves the overall reliability of the `pyrefly` type checker's ability to detect potential runtime errors related to undefined variables.

This commit **enhances the test suite** for the `pyrefly` library's **scope analysis** module by introducing two new test cases in `pyrefly/lib/test/scope.rs`. These tests specifically target **edge cases** related to variable locality: one for `del` statements within dead code branches (`test_del_in_dead_code_makes_local`) and another for conditionally defined class members (`test_conditionally_defined_class_member`). This **testing** work aims to prevent future bugs and improve the **robustness and correctness** of the Python scope analysis by ensuring proper handling of these complex scenarios.

This commit introduces **secondary annotation support** to the `pyrefly/lib/error` module, enabling significantly richer diagnostic messages. It adds a `SecondaryAnnotation` struct and integrates it into the `Error` struct, allowing for multi-span labeled annotations in error diagnostics. The `ErrorCollector` gains an `add_with_annotations` method, and the `get_source_snippet` function is updated to render these new info-level labeled spans, expanding the source range as needed. This **new capability** enhances the **error reporting and diagnostic generation system** by providing more contextual and understandable feedback to users, such as labeling different parts of an expression involved in an error.

This commit introduces a **new capability** to significantly **enhance error diagnostics** for binary and unary operations by providing detailed, multi-span type annotations. It extends the **error context** to carry operand `TextRange` information, enabling the generation of rich annotations that explicitly label each operand with its inferred type. This improvement affects the **operator type inference** in `pyrefly/lib/alt/operators.rs` and the **error reporting and display system** in `pyrefly/lib/error/`. As a result, users will now receive much clearer and more actionable error messages, such as `*` is not supported between `int | str | None` and `int`, with each operand's type clearly highlighted.

This commit introduces a **new capability** by enabling the `extra_file_extensions` field to be **deserialized from `pyrefly.toml` configuration files**. It modifies the `crates/pyrefly_config/src/config.rs` module, updating the `serde` annotation to allow reading these extensions. This change is crucial for **Configerator workspaces**, as it permits users to specify additional file types (e.g., `.cinc`, `.cconf`) that `pyrefly` should recognize as Python source files, thereby improving the flexibility and configurability of the tool.