Files
Nim/compiler
metagn b1e5dd605a fix wrong subtype relation in tuples & infer some conversions (#23228)
fixes #18125

Previously a tuple type like `(T, int)` would match an expected tuple
type `(U, int)` if `T` is a subtype of `U`. This is wrong since the
codegen does not handle type conversions of individual tuple elements in
a type conversion of an entire tuple. For this reason the compiler
already does not accept `(float, int)` for a matched type `(int, int)`,
however the code that checked for which relations are unacceptable
checked for `< isSubtype` rather than `<= isSubtype`, so subtypes were
not included in the unacceptable relations.

Update: Now only considered unacceptable when inheritance is used, as in
[`paramTypesMatch`](3379d26629/compiler/sigmatch.nim (L2252-L2254)).
Ideally subtype relations that don't need conversions, like `nil`,
`seq[empty]`, `range[0..5]` etc would be their own relation
`isConcreteSubtype` (which would also allow us to differentiate with
`openArray[T]`), but this is too big of a refactor for now.

To compensate for this making things like `let x: (Parent, int) =
(Child(), 0)` not compile (they would crash codegen before anyway but
should still work in principle), type inference for tuple constructors
is updated such that they call `fitNode` on the fields and their
expected types, so a type conversion is generated for the individual
subtype element.

(cherry picked from commit cfd69bad1a)
2024-08-31 13:44:37 +02:00
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Nim Compiler

  • This directory contains the Nim compiler written in Nim.
  • Note that this code has been translated from a bootstrapping version written in Pascal.
  • So the code is not a poster child of good Nim code.

See Internals of the Nim Compiler for more information.