typeof(a[0]) in generic proc return type gives: Error: type mismatch

[timotheecour]

typeof(a[0]) in proc return type gives: Error: type mismatch

Example

# proc fn[T](a: T, index: int): typeof(a.x) = a.x # ok
proc fn2(a: seq[int], index: int): typeof(a[0]) = a[index] # ok
# proc fn[T](a: T, index: int): typeof(a[0]) = a[index] # Error: type mismatch: got <T, int literal(0)>

Current Output

Error: type mismatch: got <T, int literal(0)>

Expected Output

works

Additional Information

05384ef 1.3.5 devel

note

I'm wondering if it's due to the way [] is hardcoded in compiler in a few places eg:

semArrGet:
x[0] = newIdentNode(getIdent(c.cache, "[]"), n.info)

  of nkCallKinds:
    # builtin slice keeps lvalue-ness:
    if getMagic(n) in {mArrGet, mSlice}:
      result = isAssignable(owner, n[1], isUnsafeAddr)

proc matches*(c: PContext, n, nOrig: PNode, m: var TCandidate) =
  if m.magic in {mArrGet, mArrPut}:

  elif op.name.s == "[]" and op.fromSystem:
    let slice = n[2].skipStmtList
    c.addSlice(n, n[1], slice[1], slice[2])
    analyseSons(c, n)
  elif op.name.s == "[]=" and op.fromSystem:
    let slice = n[2].skipStmtList
    c.addSlice(n, n[1], slice[1], slice[2])
    analyseSons(c, n)

    if ident != nil and ident.s == "[]":

[metagn]

Fixed in #24067