merge precondition message: Conflict involving builtin

[aryairani]

Conflict involving builtin

We don't have a way of rendering a builtin in a scratch file, where users resolve merge conflicts. Thus, if there is a
conflict involving a builtin, we can't perform a merge.

One way to fix this in the future would be to introduce a syntax for defining aliases in the scratch file.

Alice's branch:

project/alice> alias.type builtin.Nat MyNat

  Done.

Bob's branch:

unique type MyNat = MyNat Nat

project/alice> merge /bob

  There's a merge conflict on MyNat, but it's a builtin on one
  or both branches. We can't yet handle merge conflicts on
  builtins.

---

Sorry, I wasn't able to perform the merge:

There's a merge conflict on MyNat, but it's a builtin on one or both branches. I can't yet handle merge conflicts involving builtins.

Please eliminate this conflict by updating one branch or the other, making MyNat the same on both branches, or making neither of them a builtin, and then try the merge again.