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

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>) {}
    |                         +++

tests/ui/lint/force-warn/cap-lints-allow.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>) {}
    |                         +++

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

@@ -8,7 +8,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `--force-warn bare-trait-objects` implied by `--force-warn rust-2018-idioms`
    = help: to override `--force-warn rust-2018-idioms` add `#[allow(bare_trait_objects)]`
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
    |                         +++

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

@@ -8,7 +8,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `--force-warn bare-trait-objects` implied by `--force-warn rust-2018-idioms`
    = help: to override `--force-warn rust-2018-idioms` add `#[allow(bare_trait_objects)]`
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
    |                         +++

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

@@ -8,7 +8,7 @@ LL | pub fn function(_x: Box<SomeTrait>) {}
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `--force-warn bare-trait-objects` implied by `--force-warn rust-2018-idioms`
    = help: to override `--force-warn rust-2018-idioms` add `#[allow(bare_trait_objects)]`
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | pub fn function(_x: Box<dyn SomeTrait>) {}
    |                         +++

tests/ui/object-safety/avoid-ice-on-warning-2.old.stderr

@@ -7,7 +7,7 @@ LL | fn id<F>(f: Copy) -> usize {
    = 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 id<F>(f: dyn Copy) -> usize {
    |             +++
@@ -21,7 +21,7 @@ LL | fn id<F>(f: Copy) -> usize {
    = 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: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | fn id<F>(f: dyn Copy) -> usize {
    |             +++

tests/ui/object-safety/avoid-ice-on-warning-3.old.stderr

@@ -7,7 +7,7 @@ LL | trait B { fn f(a: A) -> A; }
    = 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 | trait B { fn f(a: dyn A) -> A; }
    |                   +++
@@ -20,7 +20,7 @@ LL | trait B { fn f(a: A) -> A; }
    |
    = 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 | trait B { fn f(a: A) -> dyn A; }
    |                         +++
@@ -33,7 +33,7 @@ LL | trait A { fn g(b: B) -> B; }
    |
    = 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 | trait A { fn g(b: dyn B) -> B; }
    |                   +++
@@ -46,7 +46,7 @@ LL | trait A { fn g(b: B) -> B; }
    |
    = 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 | trait A { fn g(b: B) -> dyn B; }
    |                         +++
@@ -60,7 +60,7 @@ LL | trait B { fn f(a: A) -> A; }
    = 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: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | trait B { fn f(a: dyn A) -> A; }
    |                   +++
@@ -96,7 +96,7 @@ LL | trait A { fn g(b: B) -> B; }
    = 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: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-help: use `dyn`
+help: if this is an object-safe trait, use `dyn`
    |
 LL | trait A { fn g(b: dyn B) -> B; }
    |                   +++

tests/ui/object-safety/avoid-ice-on-warning.old.stderr

@@ -19,7 +19,7 @@ LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
    = 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 call_this<F>(f: F) : dyn Fn(&str) + call_that {}
    |                         +++

tests/ui/object-safety/bare-trait-dont-suggest-dyn.old.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 ord_prefer_dot(s: String) -> dyn Ord {
    |                                 +++

tests/ui/parser/trait-object-trait-parens.stderr

@@ -25,7 +25,7 @@ LL |     let _: Box<(Obj) + (?Sized) + (for<'a> Trait<'a>)>;
    = 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 _: Box<dyn (Obj) + (?Sized) + (for<'a> Trait<'a>)>;
    |                +++
@@ -49,7 +49,7 @@ LL |     let _: Box<?Sized + (for<'a> Trait<'a>) + (Obj)>;
    |
    = 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 _: Box<dyn ?Sized + (for<'a> Trait<'a>) + (Obj)>;
    |                +++
@@ -73,7 +73,7 @@ LL |     let _: Box<for<'a> Trait<'a> + (Obj) + (?Sized)>;
    |
    = 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 _: Box<dyn for<'a> Trait<'a> + (Obj) + (?Sized)>;
    |                +++

tests/ui/suggestions/issue-116434-2015.rs

@@ -0,0 +1,23 @@
+trait Foo {
+    type Clone;
+    fn foo() -> Clone;
+    //~^ WARNING trait objects without an explicit `dyn` are deprecated [bare_trait_objects]
+    //~| WARNING this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+    //~| WARNING trait objects without an explicit `dyn` are deprecated [bare_trait_objects]
+    //~| WARNING this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+    //~| ERROR the trait `Clone` cannot be made into an object [E0038]
+}
+
+trait DbHandle: Sized {}
+
+trait DbInterface {
+    type DbHandle;
+    fn handle() -> DbHandle;
+    //~^ WARNING trait objects without an explicit `dyn` are deprecated [bare_trait_objects]
+    //~| WARNING this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+    //~| WARNING trait objects without an explicit `dyn` are deprecated [bare_trait_objects]
+    //~| WARNING this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+    //~| ERROR the trait `DbHandle` cannot be made into an object [E0038]
+}
+
+fn main() {}