[jrandolf]

An empty core rec group in a component panics Component::new, and wasmtime compile, with the default configuration. These all validate:

• (component (core rec)) indexes out of bounds.
• (component (core rec) (core type (module))) unwraps an Err(()).
• (component (core type (sub (array i8))) (core rec)) indexes out of bounds.

The component translator found each core rec group from the type at the group's first index, which an empty group doesn't have, so it looked past the end of the core types or at the next definition's type. Like the type section of core modules, it now iterates over the core types that the validator added for the section instead of over the section's rec groups, so empty rec groups have nothing to intern.

Found by fuzzing Wasmtime with components generated from the component model's binary grammar (bytecodealliance/wasm-tools#2796).

[alexcrichton]

Could this perhaps use a similar pattern to core modules to avoid the need to special-case here? In module_environ.rs the translation here is based on the number of types in a module, and I believe that could be done here as well by looking at the core type count within the component before/after the validator runs.

[jrandolf]

This now works like module_environ.rs. It counts the core types before and after validating the section, then interns each rec group starting from its first type. An empty rec group adds no types, so it no longer needs a special case.