This field was originally added to create hashtables based on pointer
equality. We don't use them anymore, and the caches based on
m_hash_alloc can be implemented using m_hash without any performance
impact. This commit also fixes two places where `expr_set` was used
instead of `expr_struct_set`.
This commit is also important for the Lean4 plans where `expr` will
be implemented in Lean, and fields like `m_hash_alloc` would require us
to track state.
The new test exposes the problem. Before this commit, the common
subexpressions at
```
def tst : tree → nat
| (tree.leaf v) := v
| (tree.node v l r) :=
match f v with
| tt := tst l + tst l - tst l -- <<< HERE
| ff := tst r
end
```
were not converted into a let-exprs.
Fixes#1363
After error recovery has been implemented in the elaborator, a few
assumptions made in the type context are not valid anymore since we may
be recovering from errors, and the local and metavariable contexts may
be invalid.
I used the approach used in the class environment.
- find* methods return optional<...>
- get* methods throw exception for unknown elements
Remarks:
I preserved code patterns such as
optional<local_decl> d = lctx.find_local_decl(...)
lean_assert(d)
and did not convert them into
local_decl d = lctx.get_local_decl(...)
Reason: the intention is clear that the local must be defined there.
If it is not we should analyze the problem and decide whether we should
throw an exception or not.
However, I converted code patterns such as
local_decl d = *lctx.find_local_decl(...)
into
local_decl d = lctx.get_local_decl(...)
Disclaimer: this change fixes issue #1363, but it may obfuscate other bugs.
