Without the `box` keyword, one of these two reasons is not correct, so
let's just eliminate this section and elaborate on the reason for the
legit use case inline.
Fixes#24511
At the moment, when compilation is stopped at a stop point (like `-Z parse-only`), `rustc` does not return an nonzero exit code even if there are errors (expect fatal ones, that cause it to panic immediately). As an example, compiling `src/test/compile-fail/doc-before-semi.rs` with `-Z parse-only` raises an error, but exists with 0.
Note that I could not use `sess.abort_if_errors()` in the macro, because `sess` is passed by value and move at some point.
skolemize_late_bound_regions essentially copies the entire type (most of the times it shouldn't, but it does), and match_impl runs millions of times.
Times compiling rustc, tested with
$ make -j4 rustc-stage1
$ ( time RUSTFLAGS=-Z time-passes make -j4 rustc-stage2 ) # need LLVM time for calibration
Before:
real 21m44.960s
user 29m38.812s
sys 0m14.944s
After:
real 19m31.445s
user 26m47.260s
sys 0m14.952s
Making this is a 10% performance improvement.
LLVM passes took 867 seconds before, 862 seconds after.
This implementation is currently about 3-4 times faster than using the `.to_string()` based approach.
I would also suggest we deprecate `String::from_str` since it's redundant with the stable `String::from` method, but I'll leave that for a future PR.
"Dynamically typed" didn't seem like a relevant distinction; there are statically-compiled dynamically-typed languages. Another term that might work here (despite being notoriously vague) is "scripting languages".
Apply optimization described in
https://github.com/rust-lang/regex/pull/73#issuecomment-93777126
to rust's copy of `unicode.py`.
This shrinks librustc_unicode's tables.rs from 479kB to 456kB,
and should improve performance slightly for related operations
(e.g., is_alphabetic(), is_xid_start(), etc).
In addition, pull in fix from @dscorbett's commit
d25c39f86568a147f9b7080c25711fb1f98f056a in regex, which
makes `load_properties()` more tolerant of whitespace
in the Unicode tables. (This fix does not result in any
changes to tables.rs, but could if the Unicode tables
change in the future.)
