Extend rustc_on_implemented to improve a ?-on-ControlFlow error message

3 files changed, 11 insertions, 13 deletions

diff --git a/src/test/ui/try-trait/bad-interconversion.rs b/src/test/ui/try-trait/bad-interconversion.rs
index 87585822f57..385f5510fb4 100644
--- a/src/test/ui/try-trait/bad-interconversion.rs
+++ b/src/test/ui/try-trait/bad-interconversion.rs
@@ -20,7 +20,7 @@ fn control_flow_to_result() -> Result<u64, String> {
 
 fn result_to_option() -> Option<u16> {
     Some(Err("hello")?)
-    //~^ ERROR the `?` operator can only be used on `Option`s in a function that returns `Option`
+    //~^ ERROR the `?` operator can only be used on `Option`s, not `Result`s, in a function that returns `Option`
 }
 
 fn control_flow_to_option() -> Option<u64> {
@@ -30,18 +30,18 @@ fn control_flow_to_option() -> Option<u64> {
 
 fn result_to_control_flow() -> ControlFlow<String> {
     ControlFlow::Continue(Err("hello")?)
-    //~^ ERROR the `?` operator can only be used on `ControlFlow<B, _>`s in a function that returns `ControlFlow<B, _>`
+    //~^ ERROR the `?` operator can only be used on `ControlFlow`s in a function that returns `ControlFlow`
 }
 
 fn option_to_control_flow() -> ControlFlow<u64> {
     Some(3)?;
-    //~^ ERROR the `?` operator can only be used on `ControlFlow<B, _>`s in a function that returns `ControlFlow<B, _>`
+    //~^ ERROR the `?` operator can only be used on `ControlFlow`s in a function that returns `ControlFlow`
     ControlFlow::Break(10)
 }
 
 fn control_flow_to_control_flow() -> ControlFlow<i64> {
     ControlFlow::Break(4_u8)?;
-    //~^ ERROR the `?` operator can only be used on `ControlFlow<B, _>`s in a function that returns `ControlFlow<B, _>`
+    //~^ ERROR the `?` operator in a function that returns `ControlFlow<B, _>` can only be used on other `ControlFlow<B, _>`s
     ControlFlow::Continue(())
 }
 
diff --git a/src/test/ui/try-trait/bad-interconversion.stderr b/src/test/ui/try-trait/bad-interconversion.stderr
index e396256de22..f5b315c2519 100644
--- a/src/test/ui/try-trait/bad-interconversion.stderr
+++ b/src/test/ui/try-trait/bad-interconversion.stderr
@@ -40,12 +40,12 @@ LL | | }
    = help: the trait `FromResidual<ControlFlow<{integer}, Infallible>>` is not implemented for `Result<u64, String>`
    = note: required by `from_residual`
 
-error[E0277]: the `?` operator can only be used on `Option`s in a function that returns `Option`
+error[E0277]: the `?` operator can only be used on `Option`s, not `Result`s, in a function that returns `Option`
   --> $DIR/bad-interconversion.rs:22:22
    |
 LL | / fn result_to_option() -> Option<u16> {
 LL | |     Some(Err("hello")?)
-   | |                      ^ this `?` produces `Result<Infallible, &str>`, which is incompatible with `Option<u16>`
+   | |                      ^ use `.ok()?` if you want to discard the `Result<Infallible, &str>` error information
 LL | |
 LL | | }
    | |_- this function returns an `Option`
@@ -66,7 +66,7 @@ LL | | }
    = help: the trait `FromResidual<ControlFlow<{integer}, Infallible>>` is not implemented for `Option<u64>`
    = note: required by `from_residual`
 
-error[E0277]: the `?` operator can only be used on `ControlFlow<B, _>`s in a function that returns `ControlFlow<B, _>`
+error[E0277]: the `?` operator can only be used on `ControlFlow`s in a function that returns `ControlFlow`
   --> $DIR/bad-interconversion.rs:32:39
    |
 LL | / fn result_to_control_flow() -> ControlFlow<String> {
@@ -77,10 +77,9 @@ LL | | }
    | |_- this function returns a `ControlFlow`
    |
    = help: the trait `FromResidual<Result<Infallible, &str>>` is not implemented for `ControlFlow<String>`
-   = note: unlike `Result`, there's no `From`-conversion performed for `ControlFlow`
    = note: required by `from_residual`
 
-error[E0277]: the `?` operator can only be used on `ControlFlow<B, _>`s in a function that returns `ControlFlow<B, _>`
+error[E0277]: the `?` operator can only be used on `ControlFlow`s in a function that returns `ControlFlow`
   --> $DIR/bad-interconversion.rs:37:12
    |
 LL | / fn option_to_control_flow() -> ControlFlow<u64> {
@@ -92,10 +91,9 @@ LL | | }
    | |_- this function returns a `ControlFlow`
    |
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `ControlFlow<u64>`
-   = note: unlike `Result`, there's no `From`-conversion performed for `ControlFlow`
    = note: required by `from_residual`
 
-error[E0277]: the `?` operator can only be used on `ControlFlow<B, _>`s in a function that returns `ControlFlow<B, _>`
+error[E0277]: the `?` operator in a function that returns `ControlFlow<B, _>` can only be used on other `ControlFlow<B, _>`s (with the same Break type)
   --> $DIR/bad-interconversion.rs:43:29
    |
 LL | / fn control_flow_to_control_flow() -> ControlFlow<i64> {
diff --git a/src/test/ui/try-trait/option-to-result.stderr b/src/test/ui/try-trait/option-to-result.stderr
index 92087c2aba2..9f7d80d4f23 100644
--- a/src/test/ui/try-trait/option-to-result.stderr
+++ b/src/test/ui/try-trait/option-to-result.stderr
@@ -12,13 +12,13 @@ LL | | }
    = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `Result<(), ()>`
    = note: required by `from_residual`
 
-error[E0277]: the `?` operator can only be used on `Option`s in a function that returns `Option`
+error[E0277]: the `?` operator can only be used on `Option`s, not `Result`s, in a function that returns `Option`
   --> $DIR/option-to-result.rs:11:6
    |
 LL | / fn test_option() -> Option<i32>{
 LL | |     let a:Result<i32, i32> = Ok(5);
 LL | |     a?;
-   | |      ^ this `?` produces `Result<Infallible, i32>`, which is incompatible with `Option<i32>`
+   | |      ^ use `.ok()?` if you want to discard the `Result<Infallible, i32>` error information
 LL | |     Some(5)
 LL | | }
    | |_- this function returns an `Option`