added enclosing_scope attr to Try trait and fixed ui tests accordingly

src/libcore/ops/try.rs

@@ -5,19 +5,20 @@
 /// extracting those success or failure values from an existing instance and
 /// creating a new instance from a success or failure value.
 #[unstable(feature = "try_trait", issue = "42327")]
-#[rustc_on_unimplemented(
+#[cfg_attr(not(bootstrap), rustc_on_unimplemented(
 on(all(
 any(from_method="from_error", from_method="from_ok"),
 from_desugaring="QuestionMark"),
 message="the `?` operator can only be used in {ItemContext} \
                that returns `Result` or `Option` \
                (or another type that implements `{Try}`)",
-label="cannot use the `?` operator in {ItemContext} that returns `{Self}`"),
+label="cannot use the `?` operator in {ItemContext} that returns `{Self}`",
+enclosing_scope="this function should return `Result` or `Option` to accept `?`"),
 on(all(from_method="into_result", from_desugaring="QuestionMark"),
 message="the `?` operator can only be applied to values \
                that implement `{Try}`",
 label="the `?` operator cannot be applied to type `{Self}`")
-)]
+))]
 #[doc(alias = "?")]
 pub trait Try {
     /// The type of this value when viewed as successful.

src/test/ui/async-await/try-on-option-in-async.stderr

@@ -1,8 +1,14 @@
 error[E0277]: the `?` operator can only be used in an async block that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/try-on-option-in-async.rs:8:9
    |
-LL |         x?;
-   |         ^^ cannot use the `?` operator in an async block that returns `{integer}`
+LL |       async {
+   |  ___________-
+LL | |         let x: Option<u32> = None;
+LL | |         x?;
+   | |         ^^ cannot use the `?` operator in an async block that returns `{integer}`
+LL | |         22
+LL | |     }.await
+   | |_____- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `{integer}`
    = note: required by `std::ops::Try::from_error`
@@ -10,8 +16,14 @@ LL |         x?;
 error[E0277]: the `?` operator can only be used in an async closure that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/try-on-option-in-async.rs:16:9
    |
-LL |         x?;
-   |         ^^ cannot use the `?` operator in an async closure that returns `u32`
+LL |       let async_closure = async || {
+   |  __________________________________-
+LL | |         let x: Option<u32> = None;
+LL | |         x?;
+   | |         ^^ cannot use the `?` operator in an async closure that returns `u32`
+LL | |         22_u32
+LL | |     };
+   | |_____- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `u32`
    = note: required by `std::ops::Try::from_error`
@@ -19,8 +31,14 @@ LL |         x?;
 error[E0277]: the `?` operator can only be used in an async function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/try-on-option-in-async.rs:25:5
    |
-LL |     x?;
-   |     ^^ cannot use the `?` operator in an async function that returns `u32`
+LL |   async fn an_async_function() -> u32 {
+   |  _____________________________________-
+LL | |     let x: Option<u32> = None;
+LL | |     x?;
+   | |     ^^ cannot use the `?` operator in an async function that returns `u32`
+LL | |     22
+LL | | }
+   | |_- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `u32`
    = note: required by `std::ops::Try::from_error`

src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr

@@ -575,8 +575,17 @@ LL |     if (let 0 = 0)? {}
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/disallowed-positions.rs:46:8
    |
-LL |     if (let 0 = 0)? {}
-   |        ^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`
+LL | / fn nested_within_if_expr() {
+LL | |     if &let 0 = 0 {}
+LL | |
+LL | |
+...  |
+LL | |     if (let 0 = 0)? {}
+   | |        ^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`
+...  |
+LL | |     if let true = let true = true {}
+LL | | }
+   | |_- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `()`
    = note: required by `std::ops::Try::from_error`
@@ -754,8 +763,17 @@ LL |     while (let 0 = 0)? {}
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/disallowed-positions.rs:110:11
    |
-LL |     while (let 0 = 0)? {}
-   |           ^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`
+LL | / fn nested_within_while_expr() {
+LL | |     while &let 0 = 0 {}
+LL | |
+LL | |
+...  |
+LL | |     while (let 0 = 0)? {}
+   | |           ^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`
+...  |
+LL | |     while let true = let true = true {}
+LL | | }
+   | |_- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `()`
    = note: required by `std::ops::Try::from_error`
@@ -924,8 +942,17 @@ LL |     (let 0 = 0)?;
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/disallowed-positions.rs:183:5
    |
-LL |     (let 0 = 0)?;
-   |     ^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`
+LL | / fn outside_if_and_while_expr() {
+LL | |     &let 0 = 0;
+LL | |
+LL | |     !let 0 = 0;
+...  |
+LL | |     (let 0 = 0)?;
+   | |     ^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`
+...  |
+LL | |
+LL | | }
+   | |_- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `()`
    = note: required by `std::ops::Try::from_error`

src/test/ui/try-on-option-diagnostics.stderr

@@ -1,8 +1,13 @@
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/try-on-option-diagnostics.rs:7:5
    |
-LL |     x?;
-   |     ^^ cannot use the `?` operator in a function that returns `u32`
+LL | / fn a_function() -> u32 {
+LL | |     let x: Option<u32> = None;
+LL | |     x?;
+   | |     ^^ cannot use the `?` operator in a function that returns `u32`
+LL | |     22
+LL | | }
+   | |_- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `u32`
    = note: required by `std::ops::Try::from_error`
@@ -10,8 +15,14 @@ LL |     x?;
 error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/try-on-option-diagnostics.rs:14:9
    |
-LL |         x?;
-   |         ^^ cannot use the `?` operator in a closure that returns `{integer}`
+LL |       let a_closure = || {
+   |  _____________________-
+LL | |         let x: Option<u32> = None;
+LL | |         x?;
+   | |         ^^ cannot use the `?` operator in a closure that returns `{integer}`
+LL | |         22
+LL | |     };
+   | |_____- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `{integer}`
    = note: required by `std::ops::Try::from_error`

src/test/ui/try-on-option.stderr

@@ -10,8 +10,13 @@ LL |     x?;
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/try-on-option.rs:13:5
    |
-LL |     x?;
-   |     ^^ cannot use the `?` operator in a function that returns `u32`
+LL | / fn bar() -> u32 {
+LL | |     let x: Option<u32> = None;
+LL | |     x?;
+   | |     ^^ cannot use the `?` operator in a function that returns `u32`
+LL | |     22
+LL | | }
+   | |_- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `u32`
    = note: required by `std::ops::Try::from_error`

src/test/ui/try-operator-on-main.stderr

@@ -1,8 +1,15 @@
 error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> $DIR/try-operator-on-main.rs:9:5
    |
-LL |     std::fs::File::open("foo")?;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`
+LL | / fn main() {
+LL | |     // error for a `Try` type on a non-`Try` fn
+LL | |     std::fs::File::open("foo")?;
+   | |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`
+LL | |
+...  |
+LL | |     try_trait_generic::<()>();
+LL | | }
+   | |_- this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `()`
    = note: required by `std::ops::Try::from_error`