Improve memory usage of libsyntax
Replaces some usage of `.to_string()` with `.into_string()`

Signed-off-by: Peter Atashian <retep998@gmail.com>
doc: that felt like it needed a stronger break than what comma provides

Remove trailing whitespace while at it
Fix issue #17216

The cleanup scope of for loop bindings should translated when
popped to ensure resources are not leaked.
Add regression test for issue #17216
Display the doc-block toggle on everything again.

This needs a clone otherwise each successive insertion detaches `toggle`
from the previous position.

Fixes #17125.
inlines contains in bitflags!

Closes #17210
auto merge of #17223 : retep998/rust/into_string, r=huonw

Replaces some usage of `.to_string()` with `.into_string()`
auto merge of #17227 : tshepang/rust/stronger-break, r=aturon

Remove trailing whitespace while at it
move most of front to libsyntax
move std_inject to libsyntax
move feature_gate to libsyntax
rebasing fixes
auto merge of #17160 : nick29581/rust/front, r=pcwalton

r?
auto merge of #17246 : bkoropoff/rust/issue-17216, r=pnkfelix

Trans the cleanup scope of for loop bindings so we don't leak resources.  Regression test included.

Closes #17216
auto merge of #17247 : huonw/rust/toggle-clone, r=alexcrichton

This needs a clone otherwise each successive insertion detaches `toggle`
from the previous position.

Fixes #17125.
auto merge of #17254 : gamazeps/rust/issue17210, r=alexcrichton

Closes #17210