Compiler panic with mismatched record field names

[imclerran]

Description

A mismatch between the naming of a record field in its type annotation and its definition/usage causes a compiler panic. This issue occurs under specific conditions involving optional fields in records.

Steps to Reproduce

The following minimal example reproduces the issue:

main! = \_ ->
    _ = foo { bar: 1, baz: 1 }
    Ok {}

foo : { qux ? U16, baz : U8 } -> U8
foo = \{ bar ? 0, baz } ->
    if bar == 0 then
        0
    else
        baz

Conditions

The panic occurs when:

1. A function takes a record with two or more fields, one of which must be optional.
2. The optional record field is a number type of U16/I16 or larger, Str, Bool, or possibly others (does not apply to U8/I8).
3. The optional field has one name in the type annotation but a different name is used in the definition, and the name from the definition is used in the function call.

Expected Behavior

The compiler should emit a type-checking error indicating the field name mismatch instead of panicking.

Actual Behavior

The compiler produces the following panic:

thread 'main' panicked at crates/compiler/gen_llvm/src/llvm/build.rs:5582:19:
Error in alias analysis: error in module ModName("UserApp"), function definition FuncName("\x11\x00\x00\x00\x01\x00\x00\x00\x90\x7f\x81\xfe\xe6S\xe3K"), definition of value binding ValueId(3): tuple field index 2 out of range

Additional Notes

• Reversing the types of the optional and non-optional fields (e.g., making the optional field U8 and the non-optional field U16) does not trigger the error, indicating the issue is not based on the total size of the record.

[imclerran]

More experimentation:

Type := { a : U8, b : U8 } # This will NOT trigger the bug, but changing a OR b to U16 will.

main! = \_ ->
    _ = foo { bar: { a: 1, b: 1 }, baz: 1 }
    Ok {}

foo : { qux ? Type, baz : U8 } -> U8
foo = \{ bar ? { a: 0, b: 0 }, baz } ->
    if bar.a == 0 then
        0
    else
        baz

[Anton-4]

Linking to zulip discussion: https://roc.zulipchat.com/#narrow/channel/463736-bugs/topic/Compiler.20panic.20for.20naming.20mismatch.20between.20type.20def.20and.20use/near/492352313