Generics Implementation Tasks

[danakj]

Living task list for Generics implementation

• [jonmeow] Expansion of a definition of one generic that depends on expansion of another
• [danakj] Named constraints (number of TODOs in tests or in code)
• [danakj] require decls
  • Diagnose missing impls for require [example test]
  • require allows use of named facet types in symbolic facets [test]
  • Name lookup into extend require [test]
• [danakj] extend (impls and require) doesn't yet apply inside enclosing scope, currently doesn't get applied until end of scope
• extend impl as in an interface (proposal Interface extension and final impl update #5337)
• alias in interface or constraint
• Support types other than Self in an impls requirement
  • Many tests, but one example
• .Self needs to be removed from the design, and its replacement implemented
  • need name shadowing rules for Self #3714 [test]
• require decls with requirements, both rewrite (treated as equality) and impls.
• Equality constraint requirements
• observe
• Implied constraints [example test]
• Constraints on an impl as don't do anything (other than rewrites into .Self)
• where declarations in impl definitions
• Should impl lookup distinguish and/or fallback on const and/or MaybeUnformed? #6068
• match_first
• Orphan rule
• Termination rule
• Form generics (still in proposal process)
• Need way to implicit conversions between integers of different sizes (maybe template-y?)
• Generics can't see builtin impls (e.g. ImplicitAs does not know about builtin conversions) #5750
• Compile-time known value is more specific for type structure than unknown (Including the value of non-types in the type structure) [notes] (needs proposal)
• Deduction of types in where clauses (test) (smaller test)
• Deduction of array bounds
  • As i32 paramter [test]
    • Even simpler [test/example] without arrays
  • From tuple value [test]
  • Conversion issues when we deduced the array bounds as type or IntLiteral parameter [test]
• Deduction of parameter that is a class access into generic class value [test]
• Access into symbolic associated constant with aggregate value [tests]
• Final specialization poisoning after using a concrete value [test]
• Symbolic constants in multiple where exprs match [test]
• default for interface functions and associated constants
• final for interface functions (and associated constants?)
• Associated constants shouldn't have to be complete [test]
• Compound member access in rewrite (and equality) constraints [example test]
• Default function syntax sugar (omitting .Op) (needs proposal I think still)

All of template is excluded here. We exclude variadics here (they would be a large separable task).

This list is as-of November 20, 2025. Many tasks were done prior. 😄