Type inference

# Type equality procedure

## Requirements
- Called to indicate that two types (passed as `const ::HIR::TypeRef&` from the HIR) must be the same
- Must handle cases where either of the passed typerefs point to aliased inferrence vars

## Rough procedure
- Locate real type pointed to by both arguments
- If neither have concrete information, alias the right to the left
- If both are concrete, ensure that both are equal (recursing for infer)
- If only one is concrete, alias the infer to it


# Code Elements

## Function/Method references

Needs to be able to point to functions in:
- Root namespace (with parameters)
- Trait (with two sets of parameters)
- Type impl block (with two sets of parameters)
- NOTE: Don't need to worry about trait impl blocks?
 - What about handling an associated type return (fully known)


Maybe can use separate types for each usecase?



# Hard Questions

## libgit2 inferrence quirk
Query on rust type inferrence rules (as designed/intended, not as implemented)

Can the presence of a trait impl influence type inferrence for the Self type?

- `*mut _ : Convert<*mut T>`, if there's only one type that implements that
  trait, is it valid to infer `_` based on that impl?

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