This refactor simplifies the desugar pass by reducing the number of
arguments threaded through each recursive function call.
- Add the module src string to `Env`.
- Add `line_info` to `Env` as a lazy-evaled function.
- Refactor desugar functions to take the `can::Env` struct in place of a
number of params. This is mostly a find-and-replace, but in a few
places `Vec::from_iter_in` was changed to `Vec::with_capacity_in`
followed by a `for` loop in order to avoid lifetime issues.
- Remove unnecessary linter annotations for `clippy::too_many_arguments`
When an error message reports on a symbol that was generated during
canonicalization, use text like "This value" instead of "This `123`
value". Generated symbols use the identifier index as the symbol name,
since valid Roc variables cannot begin with a number so there's no
chance of collision. We don't want to display generated symbols to the
user, so when building the error message we check if the symbol's name
starts with a digit.
Fix a bug in `dbg` expression desugaring by using the module scope to
generate unique identifiers instead of the variable store.
In the initial implementation of `dbg` expressions we used the
`VarStore` to generate unique identifiers for new variables created
during desugaring. We should have instead used the current module's
`Scope`, which handles identifiers within the module. Each scope has its
own incrementing variable count which is independent of the shared
variable store. The scope is used to generate new identifiers at other
points in canonicalization, such as when assigning a global identifier
to closures and `expect`s. It's possible that the identifier generated
for `dbg` could conflict with an identifier generated by the scope,
resulting in a confusing error.
