This flag was used by the kernel to decide whether the following
heuristic should be used to avoid unfolding `f` at `is_def_eq`.
f a =?= f b
-----------
a =?= b
This heuristic was introduced at Lean1 after a discussion with
Georges Gontier. Since this discussion, we added support for
caching failures of this heuristic. This proved to be much more
effective to attack the performance problems.
Moreover, we do not even use this flag in the `type_context::is_def_eq`
used during elaboration.
The current codebase contains only one place where this flag was set to
`false`: coercions generated at structure_cmd. This change was
made at commit
1c70514231
in the Lean2 codebase when we were not caching failures and
the kernel type checker was also used during elaboration.
- Lean strings (like std::string) may contain null characters. The
codebase was ignoring this issue.
- We now have a wrapper `string_ref` for wrapping Lean string objects in
C++. This wrapper also implements correctly the coercions std::string <-> string_ref.
Remark: I also found a few places where the code relies on the
following property which is not true
Forall s : std::string, std::string(s.c_str()) == s
- `name` object wrapper was assuming that all numerals were small
`nat` values. This is true in most cases, but the system would
crash when processing if it is a big number.
- The commit tries to make sure runtime/util/kernel are correct.
Modules that will be deleted contain many `TODO` comments
indicating they may crash and/or produce incorrect results
when strings contain null characters and numerals are big.
cc @kha
@kha: I thought about using `string` instead of `string_ref`.
We consistently use `std::string`. So, it should be fine, but I
was concerned about code readability.
After we bootstrap Lean4, we will be able to delete `lean::list`
template, and rename `lean::list_ref` to `lean::list`.
I am going to add `pair_ref` for wrapping Lean pair objects.
If we use `lean::string` instead of `lean::string_ref`, then
we should also use `lean::pair` instead of `lean::pair_ref`.
But, there is a problem in this case since we have
https://github.com/leanprover/lean4/blob/master/src/util/pair.h#L13
:(
