Limited nonzero coercion

[oli-obk]

coercing NonZero<T> to T if all the types are available at the cast site.

This is fairly limited, as (as the tests show), this does not allow "reborrowing" &NonZero<T> as &T. It also fails quickly if the types aren't fully clear at the coercion site, but only resolved later.

Also cannot aid in trait selection or similar, even if there is clearly only one option.

Related:

• Allow initializing NonZero with literals #143594
• RFC: const ergonomics for NonZero<T> rfcs#3786

cc @traviscross

[compiler-errors]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit e341923 with merge 4a4dd8e…

To cancel the try build, run the command @bors2 try cancel.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 4a4dd8e (4a4dd8eb0e65f6bfdacfb10fa73970e2a130d69a, parent: 040e2f8b9ff2d76fbe2146d6003e297ed4532088)

[rust-timer]

Finished benchmarking commit (4a4dd8e): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@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)	1.6%	[1.6%, 1.6%]	1
Regressions ❌ (secondary)	1.6%	[1.6%, 1.6%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	2
All ❌✅ (primary)	1.6%	[1.6%, 1.6%]	1

Max RSS (memory usage)

Results (primary -4.6%)

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
Improvements ✅ (primary)	-4.6%	[-4.6%, -4.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-4.6%	[-4.6%, -4.6%]	1

Cycles

Results (primary -3.1%, secondary -4.0%)

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
Improvements ✅ (primary)	-3.1%	[-3.1%, -3.1%]	1
Improvements ✅ (secondary)	-4.0%	[-4.0%, -4.0%]	1
All ❌✅ (primary)	-3.1%	[-3.1%, -3.1%]	1

Binary size

Results (secondary 0.0%)

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)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: 467.351s -> 465.395s (-0.42%)
Artifact size: 372.36 MiB -> 372.37 MiB (0.00%)

[bors]

☔ The latest upstream changes (presumably #144449) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-log-analyzer]

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 mismatched_types/non_zero_coerce_fail.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/non_zero_coerce_fail.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/non_zero_coerce_fail" "-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[E0599]: no method named `foo` found for struct `NonZero<T>` in the current scope
##[error]  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail.rs:15:7
   |
LL |     x.foo();
   |       ^^^ method not found in `NonZero<u8>`
   |
   = help: items from traits can only be used if the trait is implemented and in scope
note: `Foo` defines an item `foo`, perhaps you need to implement it
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail.rs:3:1
   |
LL | trait Foo: Sized {
   | ^^^^^^^^^^^^^^^^

error[E0599]: no method named `bar` found for struct `NonZero<T>` in the current scope
##[error]  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail.rs:17:7
   |
LL |     x.bar();
   |       ^^^ method not found in `NonZero<u8>`
   |
   = help: items from traits can only be used if the trait is implemented and in scope
note: `Foo` defines an item `bar`, perhaps you need to implement it
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail.rs:3:1
   |
LL | trait Foo: Sized {
   | ^^^^^^^^^^^^^^^^

error[E0277]: the trait bound `NonZero<u8>: Foo` is not satisfied
---
LL |     a.foo();
   |       ^^^ method not found in `NonZero<{integer}>`
   |
   = help: items from traits can only be used if the trait is implemented and in scope
note: `Foo` defines an item `foo`, perhaps you need to implement it
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail.rs:3:1
   |
LL | trait Foo: Sized {
   | ^^^^^^^^^^^^^^^^

error[E0599]: no method named `bar` found for struct `NonZero<T>` in the current scope
##[error]  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail.rs:26:7
   |
LL |     a.bar();
   |       ^^^ method not found in `NonZero<{integer}>`
   |
   = help: items from traits can only be used if the trait is implemented and in scope
note: `Foo` defines an item `bar`, perhaps you need to implement it
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail.rs:3:1
   |
LL | trait Foo: Sized {
   | ^^^^^^^^^^^^^^^^

error[E0277]: the trait bound `NonZero<{integer}>: Foo` is not satisfied
##[error]  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail.rs:28:9
   |
LL |     foo(a);
   |     --- ^ the trait `Foo` is not implemented for `NonZero<{integer}>`
   |     |
   |     required by a bound introduced by this call
---
+    | ^^^^^^^^^^^^^^^^^^^ `u8` implements `Foo<u8>`
+ LL | impl Foo<u16> for u16 {}
+    | ^^^^^^^^^^^^^^^^^^^^^ `u16` implements `Foo<u16>`
28 
29 error[E0277]: the trait bound `{integer}: Foo<NonZero<u8>>` is not satisfied
30   --> $DIR/non_zero_coerce_fail2.rs:18:11

34    |       |
35    |       required by a bound introduced by this call
36    |
-    = help: the following other types implement trait `Foo<T>`:
---
+    | ^^^^^^^^^^^^^^^^^^^ `u8` implements `Foo<u8>`
+ LL | impl Foo<u16> for u16 {}
+    | ^^^^^^^^^^^^^^^^^^^^^ `u16` implements `Foo<u16>`
68 
69 error[E0277]: the trait bound `{integer}: Foo<NonZero<u8>>` is not satisfied
70   --> $DIR/non_zero_coerce_fail2.rs:27:11

74    |       |
75    |       required by a bound introduced by this call
76    |
-    = help: the following other types implement trait `Foo<T>`:
---
To only update this specific test, also pass `--test-args mismatched_types/non_zero_coerce_fail2.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/non_zero_coerce_fail2.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/non_zero_coerce_fail2" "-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/non_zero_coerce_fail2.rs:13:14
   |
LL |     5_u8.foo(&x);
   |          --- ^^ expected `&u8`, found `&NonZero<u8>`
   |          |
   |          arguments to this method are incorrect
   |
   = note: expected reference `&u8`
              found reference `&NonZero<u8>`
note: method defined here
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:4:8
   |
LL |     fn foo(&self, other: &T) {}
   |        ^^^        ---------

error[E0277]: the trait bound `{integer}: Foo<NonZero<u8>>` is not satisfied
##[error]  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:16:11
   |
LL |     5.foo(&x);
   |       --- ^^ the trait `Foo<NonZero<u8>>` is not implemented for `{integer}`
   |       |
   |       required by a bound introduced by this call
   |
help: the following other types implement trait `Foo<T>`
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:8:1
   |
LL | impl Foo<u8> for u8 {}
   | ^^^^^^^^^^^^^^^^^^^ `u8` implements `Foo<u8>`
LL | impl Foo<u16> for u16 {}
   | ^^^^^^^^^^^^^^^^^^^^^ `u16` implements `Foo<u16>`

error[E0277]: the trait bound `{integer}: Foo<NonZero<u8>>` is not satisfied
##[error]  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:18:11
   |
LL |     5.bar(x);
   |       --- ^ the trait `Foo<NonZero<u8>>` is not implemented for `{integer}`
   |       |
   |       required by a bound introduced by this call
   |
help: the following other types implement trait `Foo<T>`
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:8:1
---

error[E0308]: mismatched types
##[error]  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:22:14
   |
LL |     5_u8.foo(&a);
   |          --- ^^ expected `&u8`, found `&NonZero<{integer}>`
   |          |
   |          arguments to this method are incorrect
   |
   = note: expected reference `&u8`
              found reference `&NonZero<{integer}>`
note: method defined here
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:4:8
   |
LL |     fn foo(&self, other: &T) {}
   |        ^^^        ---------

error[E0277]: the trait bound `{integer}: Foo<NonZero<u8>>` is not satisfied
##[error]  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:25:11
   |
LL |     5.foo(&a);
   |       --- ^^ the trait `Foo<NonZero<u8>>` is not implemented for `{integer}`
   |       |
   |       required by a bound introduced by this call
   |
help: the following other types implement trait `Foo<T>`
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:8:1
   |
LL | impl Foo<u8> for u8 {}
   | ^^^^^^^^^^^^^^^^^^^ `u8` implements `Foo<u8>`
LL | impl Foo<u16> for u16 {}
   | ^^^^^^^^^^^^^^^^^^^^^ `u16` implements `Foo<u16>`

error[E0277]: the trait bound `{integer}: Foo<NonZero<u8>>` is not satisfied
##[error]  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:27:11
   |
LL |     5.bar(a);
   |       --- ^ the trait `Foo<NonZero<u8>>` is not implemented for `{integer}`
   |       |
   |       required by a bound introduced by this call
   |
help: the following other types implement trait `Foo<T>`
  --> /checkout/tests/ui/mismatched_types/non_zero_coerce_fail2.rs:8:1