[WIP] - moving trivial field reads attr to macros by josetorrs · Pull Request #160666 · rust-lang/rust

josetorrs · 2026-08-07T01:53:59Z

part of #160621. also discussion in #t-lang > diagnostics attribute to ignore code for unused_code lints

I did not use an LLM to create a change in this PR.
I used an LLM to create a change in this PR, and I have explained below how it was used.

josetorrs · 2026-08-07T02:08:46Z

+            && let Some(macro_def_id) = impl_item.span.ctxt().outer_expn_data().macro_def_id
+            && find_attr!(self.tcx, macro_def_id, RustcTrivialFieldReads)


TBH not really sure about this but my computer has been really slow so wanted to see what CI would do

View changes since the review

rust-log-analyzer · 2026-08-07T02:29:04Z

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

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

---- [ui] tests/ui/traits/const-traits/minicore-const-fn-early-bound.rs stdout ----

error: auxiliary build of /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs failed to compile: 
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-const-fn-early-bound/auxiliary" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-Znext-solver" "-Cpanic=abort" "-L" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-const-fn-early-bound/auxiliary"
stdout: none
--- stderr -------------------------------
error: the `rustc_trivial_field_reads` attribute cannot be used on traits
##[error]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:448:3
   |
---

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:52:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:56:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `bytes`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:149:28
   |
LL |     const fn from_ne_bytes(bytes: [u8; size_of::<Self>()]) -> Self {
   |                            ^^^^^ help: if this is intentional, prefix it with an underscore: `_bytes`

warning: unused variable: `other`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:319:18
   |
LL |     fn eq(&self, other: &str) -> bool {
   |                  ^^^^^ help: if this is intentional, prefix it with an underscore: `_other`

warning: unused variable: `value`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:417:18
   |
LL |     const fn new(value: T) -> RefCell<T> {
---
---- [ui] tests/ui/traits/const-traits/minicore-deref-fail.rs stdout ----

error: auxiliary build of /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs failed to compile: 
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-deref-fail/auxiliary" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-Znext-solver" "-Cpanic=abort" "-L" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-deref-fail/auxiliary"
stdout: none
--- stderr -------------------------------
error: the `rustc_trivial_field_reads` attribute cannot be used on traits
##[error]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:448:3
   |
---

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:52:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:56:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `bytes`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:149:28
   |
LL |     const fn from_ne_bytes(bytes: [u8; size_of::<Self>()]) -> Self {
   |                            ^^^^^ help: if this is intentional, prefix it with an underscore: `_bytes`

warning: unused variable: `other`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:319:18
   |
LL |     fn eq(&self, other: &str) -> bool {
   |                  ^^^^^ help: if this is intentional, prefix it with an underscore: `_other`

warning: unused variable: `value`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:417:18
   |
LL |     const fn new(value: T) -> RefCell<T> {
---
---- [ui] tests/ui/traits/const-traits/minicore-drop-fail.rs stdout ----

error: auxiliary build of /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs failed to compile: 
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-drop-fail/auxiliary" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-Znext-solver" "-Cpanic=abort" "-L" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-drop-fail/auxiliary"
stdout: none
--- stderr -------------------------------
error: the `rustc_trivial_field_reads` attribute cannot be used on traits
##[error]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:448:3
   |
---

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:52:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:56:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `bytes`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:149:28
   |
LL |     const fn from_ne_bytes(bytes: [u8; size_of::<Self>()]) -> Self {
   |                            ^^^^^ help: if this is intentional, prefix it with an underscore: `_bytes`

warning: unused variable: `other`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:319:18
   |
LL |     fn eq(&self, other: &str) -> bool {
   |                  ^^^^^ help: if this is intentional, prefix it with an underscore: `_other`

warning: unused variable: `value`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:417:18
   |
LL |     const fn new(value: T) -> RefCell<T> {
---
---- [ui] tests/ui/traits/const-traits/minicore-drop-without-feature-gate.rs#no stdout ----

error in revision `no`: auxiliary build of /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs failed to compile: 
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--cfg" "no" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-drop-without-feature-gate.no/auxiliary" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-Znext-solver" "-Cpanic=abort" "-L" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-drop-without-feature-gate.no/auxiliary"
stdout: none
--- stderr -------------------------------
error: the `rustc_trivial_field_reads` attribute cannot be used on traits
##[error]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:448:3
   |
---

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:52:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:56:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `bytes`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:149:28
   |
LL |     const fn from_ne_bytes(bytes: [u8; size_of::<Self>()]) -> Self {
   |                            ^^^^^ help: if this is intentional, prefix it with an underscore: `_bytes`

warning: unused variable: `other`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:319:18
   |
LL |     fn eq(&self, other: &str) -> bool {
   |                  ^^^^^ help: if this is intentional, prefix it with an underscore: `_other`

warning: unused variable: `value`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:417:18
   |
LL |     const fn new(value: T) -> RefCell<T> {
---
---- [ui] tests/ui/traits/const-traits/minicore-fn-fail.rs stdout ----

error: auxiliary build of /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs failed to compile: 
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-fn-fail/auxiliary" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-Znext-solver" "-Cpanic=abort" "-L" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-fn-fail/auxiliary"
stdout: none
--- stderr -------------------------------
error: the `rustc_trivial_field_reads` attribute cannot be used on traits
##[error]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:448:3
   |
---

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:52:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:56:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `bytes`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:149:28
   |
LL |     const fn from_ne_bytes(bytes: [u8; size_of::<Self>()]) -> Self {
   |                            ^^^^^ help: if this is intentional, prefix it with an underscore: `_bytes`

warning: unused variable: `other`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:319:18
   |
LL |     fn eq(&self, other: &str) -> bool {
   |                  ^^^^^ help: if this is intentional, prefix it with an underscore: `_other`

warning: unused variable: `value`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:417:18
   |
LL |     const fn new(value: T) -> RefCell<T> {
---

---- [ui] tests/ui/traits/const-traits/minicore-fn-fail.rs stdout end ----
---- [ui] tests/ui/traits/const-traits/minicore-drop-without-feature-gate.rs#yes stdout ----

error in revision `yes`: auxiliary build of /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs failed to compile: 
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--cfg" "yes" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-drop-without-feature-gate.yes/auxiliary" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-Znext-solver" "-Cpanic=abort" "-L" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-drop-without-feature-gate.yes/auxiliary"
stdout: none
--- stderr -------------------------------
error: the `rustc_trivial_field_reads` attribute cannot be used on traits
##[error]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:448:3
   |
---

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:52:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:56:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `bytes`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:149:28
   |
LL |     const fn from_ne_bytes(bytes: [u8; size_of::<Self>()]) -> Self {
   |                            ^^^^^ help: if this is intentional, prefix it with an underscore: `_bytes`

warning: unused variable: `other`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:319:18
   |
LL |     fn eq(&self, other: &str) -> bool {
   |                  ^^^^^ help: if this is intentional, prefix it with an underscore: `_other`

warning: unused variable: `value`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:417:18
   |
LL |     const fn new(value: T) -> RefCell<T> {
---
---- [ui] tests/ui/traits/const-traits/minicore-works.rs stdout ----

error: auxiliary build of /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs failed to compile: 
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-works/auxiliary" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-Znext-solver" "-Cpanic=abort" "-L" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/const-traits/minicore-works/auxiliary"
stdout: none
--- stderr -------------------------------
error: the `rustc_trivial_field_reads` attribute cannot be used on traits
##[error]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:448:3
   |
---

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:52:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `x`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:56:9
   |
LL |     let x = 42_i32 + 43_i32;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`

warning: unused variable: `bytes`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:149:28
   |
LL |     const fn from_ne_bytes(bytes: [u8; size_of::<Self>()]) -> Self {
   |                            ^^^^^ help: if this is intentional, prefix it with an underscore: `_bytes`

warning: unused variable: `other`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:319:18
   |
LL |     fn eq(&self, other: &str) -> bool {
   |                  ^^^^^ help: if this is intentional, prefix it with an underscore: `_other`

warning: unused variable: `value`
##[warning]  --> /checkout/tests/ui/traits/const-traits/auxiliary/minicore.rs:417:18
   |
LL |     const fn new(value: T) -> RefCell<T> {

mejrs · 2026-08-08T15:44:00Z

The changes look correct so far, you just need to delete the #[rustc_trivial_field_reads] in the minicore.rs file.

mejrs · 2026-08-08T15:44:45Z

Let's see whether this affects perf so far.

@bors try @rust-timer queue

[WIP] - moving trivial field reads attr to macros

rust-bors · 2026-08-08T16:49:10Z

☀️ Try build successful (CI)
Build commit: af61126 (af61126db7562afad7eb31247e4ba2d8968c4766)
Base parent: 8b798d4 (8b798d41cc5d215ef8d5424f61b6dc2575ac738b)

rust-timer · 2026-08-08T17:32:07Z

Finished benchmarking commit (af61126): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.3%	[0.2%, 0.4%]	9
Improvements ✅ (primary)	-0.3%	[-0.4%, -0.1%]	2
Improvements ✅ (secondary)	-0.6%	[-0.6%, -0.6%]	1
All ❌✅ (primary)	-0.3%	[-0.4%, -0.1%]	2

Max RSS (memory usage)

Results (primary 2.1%, secondary 0.7%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.1%	[2.1%, 2.1%]	1
Regressions ❌ (secondary)	1.6%	[0.4%, 8.3%]	8
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.7%	[-1.4%, -0.4%]	5
All ❌✅ (primary)	2.1%	[2.1%, 2.1%]	1

Cycles

Results (secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.7%	[0.5%, 1.1%]	12
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.9%	[-2.3%, -0.5%]	7
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.1%]	40
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	23
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.1%]	40

Bootstrap: 459.298s -> 462.975s (0.80%)
Artifact size: 398.58 MiB -> 399.35 MiB (0.19%)

mejrs · 2026-08-08T19:37:50Z

Hmm that's not going to get better if we extend this to more places than implitems. Also, I've been thinking and I don't think this is the right approach.

I've been looking at the prior history of this (much discussion in #85200) and the derive expansion of tracing macros, and I think it makes most sense to implement it as suggested in #85200 (comment). Then you can also put it on manually written Debug impls for example and macros can more easily use it in a more granular way.

Meaning, this attribute shouldn't go on the macro (or the trait); the macro should put the attribute on the items it emits. To do that you'd have to

adjust what the attribute is allowed on
change the implementations (located in rustc_expand) of Debug/Clone to emit the attribute
change the macro shims in the standard library to allow the use of this attribute inside them, with #[allow_internal_unstable]
adjust the dead code pass to check for the presence of the attribute on more items

What do you think?

josetorrs · 2026-08-10T02:39:51Z

Yeah I was looking at that PR Friday night while exploring the changes for this. Also while looking the linked issues, do you think that would alleviate some of the concerns in #88900?

What do you think?

I'm using this issue as a learning experience for something a little more involved and very much appreciate your pointers but I may be the wrong person to bounce ideas off of 😅

mejrs · 2026-08-10T08:56:37Z

Also while looking the linked issues, do you think that would alleviate some of the concerns in #88900?

The changes in this PR shouldn't be user visible, so it shouldn't change anything in that respect.

That said we get issues like that with every noticeable addition of lints, I wouldn't worry about it.

josetorrs added 2 commits August 6, 2026 21:46

moving trivial field reads attr to macros

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Auto merge of #160666 - josetorrs:move-trivial-reads-to-macros, r=<try>

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[WIP] - moving trivial field reads attr to macros

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		&& let Some(macro_def_id) = impl_item.span.ctxt().outer_expn_data().macro_def_id
		&& find_attr!(self.tcx, macro_def_id, RustcTrivialFieldReads)

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Overall result: ❌✅ regressions and improvements - please read:

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