Rollup merge of #120530 - trevyn:issue-116434, r=compiler-errors

Be less confident when `dyn` suggestion is not checked for object safety

#120275 no longer checks bare traits for object safety when making a `dyn` suggestion on Rust < 2021. In this case, qualify the suggestion with a note that the trait must be object safe, to prevent user confusion as seen in #116434

r? ```@fmease```

Author: oli-obk

compiler/rustc_hir_analysis/src/astconv/lint.rs

@@ -243,7 +243,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 tcx.node_span_lint(BARE_TRAIT_OBJECTS, self_ty.hir_id, self_ty.span, msg, |lint| {
                     if self_ty.span.can_be_used_for_suggestions() {
                         lint.multipart_suggestion_verbose(
-                            "use `dyn`",
+                            "if this is an object-safe trait, use `dyn`",
                             sugg,
                             Applicability::MachineApplicable,
                         );

tests/ui/did_you_mean/bad-assoc-ty.stderr

@@ -182,7 +182,7 @@ LL | type H = Fn(u8) -> (u8)::Output;
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `#[warn(bare_trait_objects)]` on by default
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | type H = <dyn Fn(u8) -> (u8)>::Output;
    |          ++++               +

tests/ui/dyn-keyword/dyn-2018-edition-lint.stderr

@@ -11,7 +11,7 @@ note: the lint level is defined here
    |
 LL | #[deny(bare_trait_objects)]
    |        ^^^^^^^^^^^^^^^^^^
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | fn function(x: &dyn SomeTrait, y: Box<SomeTrait>) {
    |                 +++
@@ -24,7 +24,7 @@ LL | fn function(x: &SomeTrait, y: Box<SomeTrait>) {
    |
    = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | fn function(x: &SomeTrait, y: Box<dyn SomeTrait>) {
    |                                   +++
@@ -37,7 +37,7 @@ LL |     let _x: &SomeTrait = todo!();
    |
    = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |     let _x: &dyn SomeTrait = todo!();
    |              +++

tests/ui/dyn-keyword/dyn-angle-brackets.stderr

@@ -11,7 +11,7 @@ note: the lint level is defined here
    |
 LL | #![deny(bare_trait_objects)]
    |         ^^^^^^^^^^^^^^^^^^
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |         <dyn fmt::Debug>::fmt(self, f)
    |          +++

tests/ui/impl-trait/fresh-lifetime-from-bare-trait-obj-114664.stderr

@@ -7,7 +7,7 @@ LL | fn ice() -> impl AsRef<Fn(&())> {
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `#[warn(bare_trait_objects)]` on by default
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | fn ice() -> impl AsRef<dyn Fn(&())> {
    |                        +++

tests/ui/issues/issue-28344.stderr

@@ -7,7 +7,7 @@ LL |     let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `#[warn(bare_trait_objects)]` on by default
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |     let x: u8 = <dyn BitXor>::bitor(0 as u8, 0 as u8);
    |                 ++++       +
@@ -35,7 +35,7 @@ LL |     let g = BitXor::bitor;
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |     let g = <dyn BitXor>::bitor;
    |             ++++       +

tests/ui/issues/issue-58734.stderr

@@ -7,7 +7,7 @@ LL |     Trait::nonexistent(());
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `#[warn(bare_trait_objects)]` on by default
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |     <dyn Trait>::nonexistent(());
    |     ++++      +

tests/ui/issues/issue-86756.stderr

@@ -21,7 +21,7 @@ LL |     eq::<dyn, Foo>
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `#[warn(bare_trait_objects)]` on by default
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |     eq::<dyn, dyn Foo>
    |               +++

tests/ui/lint/bare-trait-objects-path.stderr

@@ -7,7 +7,7 @@ LL |     let _: Dyn::Ty;
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `#[warn(bare_trait_objects)]` on by default
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |     let _: <dyn Dyn>::Ty;
    |            ++++    +
@@ -26,7 +26,7 @@ LL |     Dyn::func();
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |     <dyn Dyn>::func();
    |     ++++    +
@@ -39,7 +39,7 @@ LL |     ::Dyn::func();
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |     <dyn (::Dyn)>::func();
    |     ++++++     ++
@@ -52,7 +52,7 @@ LL |     Dyn::CONST;
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL |     <dyn Dyn>::CONST;
    |     ++++    +

tests/ui/lint/force-warn/allowed-group-warn-by-default-lint.stderr

@@ -7,7 +7,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: requested on the command line with `--force-warn bare-trait-objects`
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
    |                         +++