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% Constaint-based type inferrence
## Information
- Strong type equalities
- `let a = b;`
- Coercion points
- `let a: &[_] = if k { b"1" } else { b"2" };`
- `if k { 1 as *const _ } else { 1 as *mut _ };`
- De/Re-structuring
- `let a = (b, c);`
- Outputs
- `let a = b + c;`
- Primitives
- `let a = 1;`
- Cast inferrence passthrough
- `let a: u32 = 0; let b = &a as *const _;`
## Ideas
- Weak equalities (e.g. for casts)
- Not needed, cast type can give what is needed
## Entries
- Type equality rule (with "can coerce" flag)
- Pointer to node for coercion
## Actions taken
- Build up ruleset from HIR
- Destructuring and re-structurings are applied directly
- E.g. New tuples/arrays, destructuring patterns, ...
- Direct equalities unify ivars
- NOTE: Dead ivars (ones that have been aliased) should be omitted from listings
- Iterate rulesets
- Apply coercions that are known to not coerce
- E.g. `str` cannot coerce to anything
- Check associated type projections
- Apply single-trait rule (If there's only one trait that could apply, use it)
- Run "revisit" nodes
- Keep going until out or rules or ambiguity is hit
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