std: avoid tearing `dbg!` prints #149869

joboet · 2025-12-10T23:37:13Z

This is an alternative to #149859. Instead of formatting everything into a string, this PR makes multi-expression dbg! expand into multiple nested matches, with the final match containing a single eprint!. By using macro recursion and relying on hygiene, this allows naming every bound value in that eprint!.

CC @orlp

r? libs

orlp · 2025-12-11T00:16:24Z

Neat solution :) I wasn't sure if we could use helper macros.

library/std/src/macros.rs

rustbot · 2025-12-12T12:25:46Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

joboet · 2025-12-12T12:26:37Z

src/tools/clippy/clippy_lints/src/dbg_macro.rs

+    loop {
+        let [arm] = arms else { unreachable!("dbg! macro expansion only has single-arm matches") };
+
+        match is_async_move_desugar(arm.body).unwrap_or(arm.body).peel_drop_temps().kind {


I'm not sure whether this is really necessary, I just copied this from above.

rust-log-analyzer · 2025-12-12T13:00:09Z

The job aarch64-gnu-llvm-20-1 failed! Check out the build log: (web) (plain enhanced) (plain)

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

To only update this specific test, also pass `--test-args delegation/ice-line-bounds-issue-148732.rs`

error: 1 errors occurred comparing output.
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/delegation/ice-line-bounds-issue-148732.rs" "-Zthreads=1" "-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" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/delegation/ice-line-bounds-issue-148732" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0106]: missing lifetime specifier
##[error]  --> /checkout/tests/ui/delegation/ice-line-bounds-issue-148732.rs:4:5
   |
---
LL | | }
   | |_^
   |
   = note: see issue #118212 <https://github.com/rust-lang/rust/issues/118212> for more information
   = help: add `#![feature(fn_delegation)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0277]: `fn() {b}` doesn't implement `Debug`
##[error]  --> /checkout/tests/ui/delegation/ice-line-bounds-issue-148732.rs:4:5
   |
LL | reuse a as b {
   |            - consider calling this function
...
---
---- [ui] tests/ui/mismatched_types/mismatched-types-issue-126222.rs stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/mismatched_types/mismatched-types-issue-126222/mismatched-types-issue-126222.stderr`
diff of stderr:

4 LL |             x => dbg!(x),
5    |                  ^^^^^^^ expected `()`, found integer
6    |
-    = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
8 help: you might have meant to return this value
9    |
10 LL |             x => return dbg!(x),

16 LL |                 dbg!(x)
17    |                 ^^^^^^^ expected `()`, found integer
18    |
-    = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
20 help: you might have meant to return this value
21    |
22 LL |                 return dbg!(x)

28 LL |             _ => dbg!(1)
29    |                  ^^^^^^^ expected `()`, found integer
30    |
-    = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
32 help: you might have meant to return this value
33    |
34 LL |             _ => return dbg!(1)

40 LL |             _ => {dbg!(1)}
41    |                   ^^^^^^^ expected `()`, found integer
42    |
-    = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
44 help: you might have meant to return this value
45    |
46 LL |             _ => {return dbg!(1)}


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args mismatched_types/mismatched-types-issue-126222.rs`

error: 1 errors occurred comparing output.
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/mismatched_types/mismatched-types-issue-126222.rs" "-Zthreads=1" "-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" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/mismatched_types/mismatched-types-issue-126222" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/mismatched_types/mismatched-types-issue-126222.rs:7:18
   |
LL |             x => dbg!(x), //~ ERROR mismatched types
   |                  ^^^^^^^ expected `()`, found integer
   |
   = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: you might have meant to return this value
   |
LL |             x => return dbg!(x), //~ ERROR mismatched types
   |                  ++++++

error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/mismatched_types/mismatched-types-issue-126222.rs:15:17
   |
LL |                 dbg!(x) //~ ERROR mismatched types
   |                 ^^^^^^^ expected `()`, found integer
   |
   = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: you might have meant to return this value
   |
LL |                 return dbg!(x) //~ ERROR mismatched types
   |                 ++++++

error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/mismatched_types/mismatched-types-issue-126222.rs:23:18
   |
LL |             _ => dbg!(1) //~ ERROR mismatched types
   |                  ^^^^^^^ expected `()`, found integer
   |
   = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: you might have meant to return this value
   |
LL |             _ => return dbg!(1) //~ ERROR mismatched types
   |                  ++++++

error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/mismatched_types/mismatched-types-issue-126222.rs:30:19
   |
LL |             _ => {dbg!(1)} //~ ERROR mismatched types
   |                   ^^^^^^^ expected `()`, found integer
   |
   = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: you might have meant to return this value
   |
LL |             _ => {return dbg!(1)} //~ ERROR mismatched types
   |                   ++++++

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0308`.
---
diff of stderr:

5     |     ^^^^^^^^^^^^^^^^ the trait `Debug` is not implemented for `Dummy`
6     |
7     = note: add `#[derive(Debug)]` to `Dummy` or manually `impl Debug for Dummy`
-     = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+     = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
9 help: consider annotating `Dummy` with `#[derive(Debug)]`
10    --> $DIR/auxiliary/dummy_lib.rs:2:1
11     |


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args modules/issue-107649.rs`

error: 1 errors occurred comparing output.
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/modules/issue-107649.rs" "-Zthreads=1" "-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" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/modules/issue-107649" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-Z" "ui-testing=no"
stdout: none
--- stderr -------------------------------
error[E0277]: `Dummy` doesn't implement `Debug`
##[error]   --> /checkout/tests/ui/modules/issue-107649.rs:105:5
    |
105 |     dbg!(lib::Dummy); //~ ERROR `Dummy` doesn't implement `Debug`
    |     ^^^^^^^^^^^^^^^^ the trait `Debug` is not implemented for `Dummy`
    |
    = note: add `#[derive(Debug)]` to `Dummy` or manually `impl Debug for Dummy`
    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider annotating `Dummy` with `#[derive(Debug)]`
   --> /checkout/tests/ui/modules/auxiliary/dummy_lib.rs:2:1
    |
  2 + #[derive(Debug)]
  3 | pub struct Dummy;
    |

---
---- [ui] tests/ui/rfcs/rfc-2361-dbg-macro/dbg-macro-move-semantics.rs stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/rfcs/rfc-2361-dbg-macro/dbg-macro-move-semantics/dbg-macro-move-semantics.stderr`
diff of stderr:

8 LL |     let _ = dbg!(a);
9    |             ^^^^^^^ value used here after move
10    |
-    = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
12 help: consider borrowing instead of transferring ownership
13    |
14 LL |     let _ = dbg!(&a);


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args rfcs/rfc-2361-dbg-macro/dbg-macro-move-semantics.rs`

error: 1 errors occurred comparing output.
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/rfcs/rfc-2361-dbg-macro/dbg-macro-move-semantics.rs" "-Zthreads=1" "-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" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/rfcs/rfc-2361-dbg-macro/dbg-macro-move-semantics" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0382]: use of moved value: `a`
##[error]  --> /checkout/tests/ui/rfcs/rfc-2361-dbg-macro/dbg-macro-move-semantics.rs:9:13
   |
LL |     let a = NoCopy(0);
   |         - move occurs because `a` has type `NoCopy`, which does not implement the `Copy` trait
LL |     let _ = dbg!(a);
   |             ------- value moved here
LL |     let _ = dbg!(a); //~ ERROR use of moved value
   |             ^^^^^^^ value used here after move
   |
   = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider borrowing instead of transferring ownership
   |
LL |     let _ = dbg!(&a);
   |                  +

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0382`.
---
diff of stderr:

5    |                       ^^^^^^^^^^^^^^ the trait `Debug` is not implemented for `NotDebug`
6    |
7    = note: add `#[derive(Debug)]` to `NotDebug` or manually `impl Debug for NotDebug`
-    = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
9 help: consider annotating `NotDebug` with `#[derive(Debug)]`
10    |
11 LL + #[derive(Debug)]


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args rfcs/rfc-2361-dbg-macro/dbg-macro-requires-debug.rs`

error: 1 errors occurred comparing output.
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/rfcs/rfc-2361-dbg-macro/dbg-macro-requires-debug.rs" "-Zthreads=1" "-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" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/rfcs/rfc-2361-dbg-macro/dbg-macro-requires-debug" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0277]: `NotDebug` doesn't implement `Debug`
##[error]  --> /checkout/tests/ui/rfcs/rfc-2361-dbg-macro/dbg-macro-requires-debug.rs:9:23
   |
LL |     let _: NotDebug = dbg!(NotDebug); //~ ERROR `NotDebug` doesn't implement `Debug`
   |                       ^^^^^^^^^^^^^^ the trait `Debug` is not implemented for `NotDebug`
   |
   = note: add `#[derive(Debug)]` to `NotDebug` or manually `impl Debug for NotDebug`
   = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider annotating `NotDebug` with `#[derive(Debug)]`
   |
LL + #[derive(Debug)]
LL | struct NotDebug;
   |

---
---- [ui] tests/ui/typeck/closure-ty-mismatch-issue-128561.rs stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/typeck/closure-ty-mismatch-issue-128561/closure-ty-mismatch-issue-128561.stderr`
diff of stderr:

15 LL |     b"abc".iter().for_each(|x| dbg!(x));
16    |                                ^^^^^^^ expected `()`, found `&u8`
17    |
-    = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
19 
20 error[E0308]: mismatched types
---
To only update this specific test, also pass `--test-args typeck/closure-ty-mismatch-issue-128561.rs`

error: 1 errors occurred comparing output.
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/typeck/closure-ty-mismatch-issue-128561.rs" "-Zthreads=1" "-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" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/typeck/closure-ty-mismatch-issue-128561" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/typeck/closure-ty-mismatch-issue-128561.rs:2:32
   |
LL |     b"abc".iter().for_each(|x| x); //~ ERROR: mismatched types
   |                                ^ expected `()`, found `&u8`
   |
help: consider ignoring the value
   |
LL |     b"abc".iter().for_each(|x| _ = x); //~ ERROR: mismatched types
   |                                +++

error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/typeck/closure-ty-mismatch-issue-128561.rs:4:32
   |
LL |     b"abc".iter().for_each(|x| dbg!(x)); //~ ERROR: mismatched types
   |                                ^^^^^^^ expected `()`, found `&u8`
   |
   = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/typeck/closure-ty-mismatch-issue-128561.rs:8:9
   |
LL |         x //~ ERROR: mismatched types
   |         ^ expected `()`, found `&u8`

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0308`.
------------------------------------------

---- [ui] tests/ui/typeck/closure-ty-mismatch-issue-128561.rs stdout end ----
---- [ui] tests/ui/typeck/suggestions/suggest-clone-in-macro-issue-139253.rs stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/typeck/suggestions/suggest-clone-in-macro-issue-139253/suggest-clone-in-macro-issue-139253.stderr`
diff of stderr:

26 LL |     let c: S = dbg!(field);
27    |                ^^^^^^^^^^^ expected `S`, found `&S`
28    |
-    = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
30 help: consider using clone here
31    |
32 LL |     let c: S = dbg!(field).clone();

38 LL |     let c: S = dbg!(dbg!(field));
39    |                ^^^^^^^^^^^^^^^^^ expected `S`, found `&S`
40    |
-    = note: this error originates in the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
+    = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
42 help: consider using clone here
43    |
44 LL |     let c: S = dbg!(dbg!(field)).clone();


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args typeck/suggestions/suggest-clone-in-macro-issue-139253.rs`

error: 1 errors occurred comparing output.
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/typeck/suggestions/suggest-clone-in-macro-issue-139253.rs" "-Zthreads=1" "-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" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/typeck/suggestions/suggest-clone-in-macro-issue-139253" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/typeck/suggestions/suggest-clone-in-macro-issue-139253.rs:13:34
   |
LL |     let a: Struct = dbg!(expand!(field)); //~ ERROR mismatched types [E0308]
   |                                  ^^^^^ expected `S`, found `&S`
   |
help: consider using clone here
   |
LL |     let a: Struct = dbg!(expand!(field: field.clone())); //~ ERROR mismatched types [E0308]
   |                                       +++++++++++++++

error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/typeck/suggestions/suggest-clone-in-macro-issue-139253.rs:14:35
   |
LL |     let b: Struct = dbg!(Struct { field }); //~ ERROR mismatched types [E0308]
   |                                   ^^^^^ expected `S`, found `&S`
   |
help: consider using clone here
   |
LL |     let b: Struct = dbg!(Struct { field: field.clone() }); //~ ERROR mismatched types [E0308]
   |                                        +++++++++++++++

error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/typeck/suggestions/suggest-clone-in-macro-issue-139253.rs:15:16
   |
LL |     let c: S = dbg!(field); //~ ERROR mismatched types [E0308]
   |                ^^^^^^^^^^^ expected `S`, found `&S`
   |
   = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider using clone here
   |
LL |     let c: S = dbg!(field).clone(); //~ ERROR mismatched types [E0308]
   |                           ++++++++

error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/typeck/suggestions/suggest-clone-in-macro-issue-139253.rs:16:16
   |
LL |     let c: S = dbg!(dbg!(field)); //~ ERROR mismatched types [E0308]
   |                ^^^^^^^^^^^^^^^^^ expected `S`, found `&S`
   |
   = note: this error originates in the macro `$crate::macros::dbg_internal` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider using clone here
   |
LL |     let c: S = dbg!(dbg!(field)).clone(); //~ ERROR mismatched types [E0308]
   |                                 ++++++++

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0308`.

rustbot assigned Mark-Simulacrum Dec 10, 2025

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Dec 10, 2025

joboet mentioned this pull request Dec 10, 2025

Avoid tearing dbg! prints #149859

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orlp suggested changes Dec 11, 2025

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joboet added 2 commits December 12, 2025 12:55

std: avoid tearing dbg! prints

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update dbg! clippy lint

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joboet force-pushed the torn-dbg branch from f4c01b6 to ecb2f4a Compare December 12, 2025 12:24

rustbot added the T-clippy Relevant to the Clippy team. label Dec 12, 2025

joboet marked this pull request as ready for review December 12, 2025 12:25

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 12, 2025

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Dec 12, 2025

joboet commented Dec 12, 2025

View reviewed changes

Jamesbarford added this to Arm Maintainers Dec 12, 2025

Jamesbarford moved this to Blocked By LLVM in Arm Maintainers Dec 12, 2025

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std: avoid tearing `dbg!` prints #149869

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