Previously, there was a function `opaque fromUTF8Unchecked : ByteArray
-> String` which would convert a list of bytes into a string, but as the
name implies it does not validate that the string is UTF-8 before doing
so and as a result it produces unsound results in the compiler (because
the lean model of `String` indirectly asserts UTF-8 validity). This PR
replaces that function by
```lean
opaque validateUTF8 (a : @& ByteArray) : Bool
opaque fromUTF8 (a : @& ByteArray) (h : validateUTF8 a) : String
```
so that while the function is still "unchecked", we have a proof witness
that the string is valid. To recover the original, actually unchecked
version, use `lcProof` or other unsafe methods to produce the proof
witness.
Because this was the only `ByteArray -> String` conversion function, it
was used in several places in an unsound way (e.g. reading untrusted
input from IO and treating it as UTF-8). These have been replaced by
`fromUTF8?` or `fromUTF8!` as appropriate.
[Before](https://github.com/leanprover/lean4/files/14772220/oi.pdf) and
[after](https://github.com/leanprover/lean4/files/14772226/oi2.pdf).
This gets `ByteArray`, `String.Extra`, `ToString.Macro` and `RCases` out
of the imports of `omega`. I'd hoped to get `Array.Subarray` too, but
it's tangled up in the list literal syntax. Further progress could come
from make `split` use available `Decidable` instances, so we could pull
out `Classical` (and possibly some of `PropLemmas`).
This is pretty big PR that upstreams all of Std.Data.Int.Init in one go.
So far lemmas have seen minimal changes needed to adapt to Lean core
environment.
---------
Co-authored-by: Scott Morrison <scott.morrison@gmail.com>
This is used in the "Try this:" widget machinery powering `simp?`.
There is a test file in Std, which I am not upstreaming at the same
time, as that relies on more code actions / #guard_msgs material. That
test file will still of course test things from Std, and later it can be
reunited with the code it is testing.
---------
Co-authored-by: Leonardo de Moura <leomoura@amazon.com>
The previous type was
```
Lean.instFromJsonProd.{u, v} {α β : Type (max u v)} [FromJson α] [FromJson β] :
FromJson (α × β)
```
where universe metavariable assignment assigned the wrong universe to both types!
