diagnostics: make implicit Sized bounds explicit in E0277

[Daniel-B-Smith]

When a trait parameter depends upon Sized, the error message only referred to the full trait itself and didn't mention Sized. This makes the failure to implement Sized explicit. It also notes when the Sized trait bound is explicit or implicit.

Fixes #150576

[rustbot]

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[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rustbot]

⚠️ Warning ⚠️

• The following commits have merge commits (commits with multiple parents) in your changes. We have a no merge policy so these commits will need to be removed for this pull request to be merged.

  • f1b51ac

  You can start a rebase with the following commands:

  $ # rebase
  $ git pull --rebase https://github.com/rust-lang/rust.git main
  $ git push --force-with-lease
  

[Daniel-B-Smith]

Reverting to draft while I fix the tests. My apologies for the noise.

[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)

diff of stderr:

17   --> $DIR/slice-issue-87994.rs:3:12
18    |
19 LL |   for _ in v[1..] {
-    |            ^^^^^^ the trait `IntoIterator` is not implemented for `[i32]`
+    |            ^^^^^^ the trait `Sized` is not implemented for `[i32]`
21    |
22    = note: the trait bound `[i32]: IntoIterator` is not satisfied
23    = note: required for `[i32]` to implement `IntoIterator`

-    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
25 help: consider borrowing here
26    |
27 LL |   for _ in &v[1..] {

48   --> $DIR/slice-issue-87994.rs:11:13
49    |
50 LL |   for i2 in v2[1..] {
-    |             ^^^^^^^ the trait `IntoIterator` is not implemented for `[K]`
+    |             ^^^^^^^ the trait `Sized` is not implemented for `[K]`
52    |
53    = note: the trait bound `[K]: IntoIterator` is not satisfied
54    = note: required for `[K]` to implement `IntoIterator`

-    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
56 help: consider borrowing here
57    |
58 LL |   for i2 in &v2[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 suggestions/slice-issue-87994.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/suggestions/slice-issue-87994.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/suggestions/slice-issue-87994" "-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]: `[i32]` is not an iterator
##[error]  --> /checkout/tests/ui/suggestions/slice-issue-87994.rs:3:12
   |
LL |   for _ in v[1..] {
   |            ^^^^^^ the trait `IntoIterator` is not implemented for `[i32]`
   |
   = note: the trait bound `[i32]: IntoIterator` is not satisfied
   = note: required for `[i32]` to implement `IntoIterator`
help: consider borrowing here
   |
LL |   for _ in &v[1..] {
   |            +
LL |   for _ in &mut v[1..] {
   |            ++++

error[E0277]: `[i32]` is not an iterator
##[error]  --> /checkout/tests/ui/suggestions/slice-issue-87994.rs:3:12
   |
LL |   for _ in v[1..] {
   |            ^^^^^^ the trait `Sized` is not implemented for `[i32]`
   |
   = note: the trait bound `[i32]: IntoIterator` is not satisfied
   = note: required for `[i32]` to implement `IntoIterator`
help: consider borrowing here
   |
LL |   for _ in &v[1..] {
   |            +
LL |   for _ in &mut v[1..] {
   |            ++++

error[E0277]: `[K]` is not an iterator
##[error]  --> /checkout/tests/ui/suggestions/slice-issue-87994.rs:11:13
   |
LL |   for i2 in v2[1..] {
   |             ^^^^^^^ the trait `IntoIterator` is not implemented for `[K]`
   |
   = note: the trait bound `[K]: IntoIterator` is not satisfied
   = note: required for `[K]` to implement `IntoIterator`
help: consider borrowing here
   |
LL |   for i2 in &v2[1..] {
   |             +
LL |   for i2 in &mut v2[1..] {
   |             ++++

error[E0277]: `[K]` is not an iterator
##[error]  --> /checkout/tests/ui/suggestions/slice-issue-87994.rs:11:13
   |
LL |   for i2 in v2[1..] {
   |             ^^^^^^^ the trait `Sized` is not implemented for `[K]`
   |
   = note: the trait bound `[K]: IntoIterator` is not satisfied
   = note: required for `[K]` to implement `IntoIterator`
help: consider borrowing here
   |
LL |   for i2 in &v2[1..] {
   |             +
LL |   for i2 in &mut v2[1..] {
   |             ++++

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0277`.
---
To only update this specific test, also pass `--test-args traits/dyn-iterator-deref-in-for-loop.rs`

error in revision `current`: 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/traits/dyn-iterator-deref-in-for-loop.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" "--cfg" "current" "--check-cfg" "cfg(test,FALSE,current,next)" "--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/traits/dyn-iterator-deref-in-for-loop.current" "-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]: `dyn Iterator<Item = &'a mut u8>` is not an iterator
##[error]  --> /checkout/tests/ui/traits/dyn-iterator-deref-in-for-loop.rs:9:17
   |
---
------------------------------------------

---- [ui] tests/ui/traits/dyn-iterator-deref-in-for-loop.rs#current stdout end ----
---- [ui] tests/ui/traits/dyn-iterator-deref-in-for-loop.rs#next stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/traits/dyn-iterator-deref-in-for-loop.next/dyn-iterator-deref-in-for-loop.next.stderr`
diff of stderr:

2   --> $DIR/dyn-iterator-deref-in-for-loop.rs:9:17
3    |
4 LL |     for item in *things {
---
To only update this specific test, also pass `--test-args traits/dyn-iterator-deref-in-for-loop.rs`

error in revision `next`: 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/traits/dyn-iterator-deref-in-for-loop.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" "--cfg" "next" "--check-cfg" "cfg(test,FALSE,current,next)" "--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/traits/dyn-iterator-deref-in-for-loop.next" "-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" "-Znext-solver"
stdout: none
--- stderr -------------------------------
error[E0277]: `dyn Iterator<Item = &'a mut u8>` is not an iterator
##[error]  --> /checkout/tests/ui/traits/dyn-iterator-deref-in-for-loop.rs:9:17
   |