Make Rc<T>::deref zero-cost

[EFanZh]

This PR makes Rc::deref zero-cost by changing the internal pointer so that it points to the value directly instead of the allocation.

This is split out from #132553, which will also make Arc::deref zero-cost.

[rust-log-analyzer]

The job mingw-check-tidy failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

info: removing rustup binaries
info: rustup is uninstalled
##[group]Image checksum input
mingw-check-tidy
# We use the ghcr base image because ghcr doesn't have a rate limit
# and the mingw-check-tidy job doesn't cache docker images in CI.
FROM ghcr.io/rust-lang/ubuntu:22.04

ARG DEBIAN_FRONTEND=noninteractive
RUN apt-get update && apt-get install -y --no-install-recommends \
  g++ \
---

COPY host-x86_64/mingw-check/validate-toolstate.sh /scripts/
COPY host-x86_64/mingw-check/validate-error-codes.sh /scripts/

# NOTE: intentionally uses python2 for x.py so we can test it still works.
# validate-toolstate only runs in our CI, so it's ok for it to only support python3.
ENV SCRIPT TIDY_PRINT_DIFF=1 python2.7 ../x.py test \
           --stage 0 src/tools/tidy tidyselftest --extra-checks=py,cpp
#
# This file is autogenerated by pip-compile with Python 3.10
# by the following command:
#
#    pip-compile --allow-unsafe --generate-hashes reuse-requirements.in
---
#12 2.884 Building wheels for collected packages: reuse
#12 2.885   Building wheel for reuse (pyproject.toml): started
#12 3.101   Building wheel for reuse (pyproject.toml): finished with status 'done'
#12 3.102   Created wheel for reuse: filename=reuse-4.0.3-cp310-cp310-manylinux_2_35_x86_64.whl size=132719 sha256=d2a2565e7037ad3883fb9337653f2e25bbb588534fbef3697286cbc26d1bf634
#12 3.103   Stored in directory: /tmp/pip-ephem-wheel-cache-inxvpxk2/wheels/3d/8d/0a/e0fc6aba4494b28a967ab5eaf951c121d9c677958714e34532
#12 3.105 Successfully built reuse
#12 3.105 Installing collected packages: boolean-py, binaryornot, tomlkit, reuse, python-debian, markupsafe, license-expression, jinja2, chardet, attrs
#12 3.504 Successfully installed attrs-23.2.0 binaryornot-0.4.4 boolean-py-4.0 chardet-5.2.0 jinja2-3.1.4 license-expression-30.3.0 markupsafe-2.1.5 python-debian-0.1.49 reuse-4.0.3 tomlkit-0.13.0
#12 3.504 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
#12 4.048 Collecting virtualenv
#12 4.098   Downloading virtualenv-20.31.2-py3-none-any.whl (6.1 MB)
#12 4.302      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 6.1/6.1 MB 30.0 MB/s eta 0:00:00
#12 4.367 Collecting filelock<4,>=3.12.2
#12 4.374   Downloading filelock-3.18.0-py3-none-any.whl (16 kB)
#12 4.396 Collecting distlib<1,>=0.3.7
#12 4.404   Downloading distlib-0.3.9-py2.py3-none-any.whl (468 kB)
#12 4.415      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 469.0/469.0 KB 52.5 MB/s eta 0:00:00
#12 4.451 Collecting platformdirs<5,>=3.9.1
#12 4.459   Downloading platformdirs-4.3.8-py3-none-any.whl (18 kB)
#12 4.540 Installing collected packages: distlib, platformdirs, filelock, virtualenv
#12 4.730 Successfully installed distlib-0.3.9 filelock-3.18.0 platformdirs-4.3.8 virtualenv-20.31.2
#12 4.730 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
#12 DONE 4.8s

#13 [7/8] COPY host-x86_64/mingw-check/validate-toolstate.sh /scripts/
#13 DONE 0.0s
---
DirectMap4k:      137152 kB
DirectMap2M:     8251392 kB
DirectMap1G:    10485760 kB
##[endgroup]
Executing TIDY_PRINT_DIFF=1 python2.7 ../x.py test            --stage 0 src/tools/tidy tidyselftest --extra-checks=py,cpp
+ TIDY_PRINT_DIFF=1 python2.7 ../x.py test --stage 0 src/tools/tidy tidyselftest --extra-checks=py,cpp
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.05s
##[endgroup]
WARN: currently no CI rustc builds have rustc debug assertions enabled. Please either set `rust.debug-assertions` to `false` if you want to use download CI rustc or set `rust.download-rustc` to `false`.
downloading https://static.rust-lang.org/dist/2025-05-12/rustfmt-nightly-x86_64-unknown-linux-gnu.tar.xz
---
fmt check
fmt: checked 6028 files
tidy check
tidy: Skipping binary file check, read-only filesystem
removing old virtual environment
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'venv'
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'virtualenv'
Requirement already satisfied: pip in ./build/venv/lib/python3.10/site-packages (25.1.1)
linting python files
All checks passed!
checking python file formatting
Would reformat: /checkout/src/etc/lldb_providers.py
1 file would be reformatted, 25 files already formatted

python formatting does not match! Printing diff:
1 file would be reformatted, 25 files already formatted
--- /checkout/src/etc/lldb_providers.py
+++ /checkout/src/etc/lldb_providers.py
@@ -1190,7 +1190,9 @@
         self.valobj = valobj
 
         if is_atomic:
-            self.ptr = unwrap_unique_or_non_null(self.valobj.GetChildMemberWithName("ptr"))
+            self.ptr = unwrap_unique_or_non_null(
+                self.valobj.GetChildMemberWithName("ptr")
+            )
 
             self.value = self.ptr.GetChildMemberWithName("data")
 

rerun tidy with `--extra-checks=py:fmt --bless` to reformat Python code
tidy error: checks with external tool 'ruff' failed
some tidy checks failed
Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:01:42
  local time: Wed May 21 14:25:30 UTC 2025
  network time: Wed, 21 May 2025 14:25:30 GMT
##[error]Process completed with exit code 1.
Post job cleanup.