On borrow return type, suggest borrowing from arg or owned return type

src/tools/tidy/src/ui_tests.rs

@@ -11,7 +11,7 @@ use std::path::{Path, PathBuf};
 const ENTRY_LIMIT: usize = 900;
 // FIXME: The following limits should be reduced eventually.
 const ISSUES_ENTRY_LIMIT: usize = 1852;
-const ROOT_ENTRY_LIMIT: usize = 867;
+const ROOT_ENTRY_LIMIT: usize = 866;
 
 const EXPECTED_TEST_FILE_EXTENSIONS: &[&str] = &[
     "rs",     // test source files

tests/ui/associated-types/bound-lifetime-in-binding-only.elision.stderr

@@ -5,10 +5,15 @@ LL | fn elision<T: Fn() -> &i32>() {
    |                       ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL | fn elision<T: Fn() -> &'static i32>() {
    |                        +++++++
+help: instead, you are more likely to want to return an owned value
+   |
+LL - fn elision<T: Fn() -> &i32>() {
+LL + fn elision<T: Fn() -> i32>() {
+   |
 
 error: aborting due to previous error
 

tests/ui/associated-types/bound-lifetime-in-return-only.elision.stderr

@@ -5,10 +5,15 @@ LL | fn elision(_: fn() -> &i32) {
    |                       ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL | fn elision(_: fn() -> &'static i32) {
    |                        +++++++
+help: instead, you are more likely to want to return an owned value
+   |
+LL - fn elision(_: fn() -> &i32) {
+LL + fn elision(_: fn() -> i32) {
+   |
 
 error: aborting due to previous error
 

tests/ui/c-variadic/variadic-ffi-6.stderr

@@ -5,10 +5,19 @@ LL | ) -> &usize {
    |      ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL | ) -> &'static usize {
    |       +++++++
+help: instead, you are more likely to want to change one of the arguments to be borrowed...
+   |
+LL |     x: &usize,
+   |        +
+help: ...or alternatively, you might want to return an owned value
+   |
+LL - ) -> &usize {
+LL + ) -> usize {
+   |
 
 error: aborting due to previous error
 

tests/ui/foreign-fn-return-lifetime.rs

@@ -1,5 +1,3 @@
-// run-rustfix
-
 extern "C" {
     pub fn g(_: &u8) -> &u8; // OK
     pub fn f() -> &u8; //~ ERROR missing lifetime specifier

tests/ui/foreign-fn-return-lifetime.stderr

@@ -1,14 +1,19 @@
 error[E0106]: missing lifetime specifier
-  --> $DIR/foreign-fn-return-lifetime.rs:5:19
+  --> $DIR/foreign-fn-return-lifetime.rs:3:19
    |
 LL |     pub fn f() -> &u8;
    |                   ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL |     pub fn f() -> &'static u8;
    |                    +++++++
+help: instead, you are more likely to want to return an owned value
+   |
+LL -     pub fn f() -> &u8;
+LL +     pub fn f() -> u8;
+   |
 
 error: aborting due to previous error
 

tests/ui/generic-associated-types/issue-70304.stderr

@@ -11,7 +11,7 @@ LL | fn create_doc() -> impl Document<Cursor<'_> = DocCursorImpl<'_>> {
    |                                                             ^^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`, or if you will only have owned values
    |
 LL | fn create_doc() -> impl Document<Cursor<'_> = DocCursorImpl<'static>> {
    |                                                             ~~~~~~~

tests/ui/impl-trait/impl-fn-hrtb-bounds.stderr

@@ -5,7 +5,7 @@ LL | fn d() -> impl Fn() -> (impl Debug + '_) {
    |                                      ^^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`, or if you will only have owned values
    |
 LL | fn d() -> impl Fn() -> (impl Debug + 'static) {
    |                                      ~~~~~~~

tests/ui/issues/issue-13497.stderr

@@ -5,10 +5,14 @@ LL |     &str
    |     ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL |     &'static str
    |      +++++++
+help: instead, you are more likely to want to return an owned value
+   |
+LL |     String
+   |     ~~~~~~
 
 error: aborting due to previous error
 

tests/ui/lifetimes/issue-26638.stderr

@@ -17,10 +17,18 @@ LL | fn parse_type_2(iter: fn(&u8)->&u8) -> &str { iter() }
    |                                        ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL | fn parse_type_2(iter: fn(&u8)->&u8) -> &'static str { iter() }
    |                                         +++++++
+help: instead, you are more likely to want to change the argument to be borrowed...
+   |
+LL | fn parse_type_2(iter: &fn(&u8)->&u8) -> &str { iter() }
+   |                       +
+help: ...or alternatively, you might want to return an owned value
+   |
+LL | fn parse_type_2(iter: fn(&u8)->&u8) -> String { iter() }
+   |                                        ~~~~~~
 
 error[E0106]: missing lifetime specifier
   --> $DIR/issue-26638.rs:10:22
@@ -29,10 +37,14 @@ LL | fn parse_type_3() -> &str { unimplemented!() }
    |                      ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL | fn parse_type_3() -> &'static str { unimplemented!() }
    |                       +++++++
+help: instead, you are more likely to want to return an owned value
+   |
+LL | fn parse_type_3() -> String { unimplemented!() }
+   |                      ~~~~~~
 
 error[E0308]: mismatched types
   --> $DIR/issue-26638.rs:1:69

tests/ui/lifetimes/lifetime-elision-return-type-requires-explicit-lifetime.stderr

@@ -5,10 +5,15 @@ LL | fn f() -> &isize {
    |           ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL | fn f() -> &'static isize {
    |            +++++++
+help: instead, you are more likely to want to return an owned value
+   |
+LL - fn f() -> &isize {
+LL + fn f() -> isize {
+   |
 
 error[E0106]: missing lifetime specifier
   --> $DIR/lifetime-elision-return-type-requires-explicit-lifetime.rs:7:33
@@ -41,10 +46,19 @@ LL | fn i(_x: isize) -> &isize {
    |                    ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL | fn i(_x: isize) -> &'static isize {
    |                     +++++++
+help: instead, you are more likely to want to change the argument to be borrowed...
+   |
+LL | fn i(_x: &isize) -> &isize {
+   |          +
+help: ...or alternatively, you might want to return an owned value
+   |
+LL - fn i(_x: isize) -> &isize {
+LL + fn i(_x: isize) -> isize {
+   |
 
 error[E0106]: missing lifetime specifier
   --> $DIR/lifetime-elision-return-type-requires-explicit-lifetime.rs:34:24
@@ -53,10 +67,19 @@ LL | fn j(_x: StaticStr) -> &isize {
    |                        ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL | fn j(_x: StaticStr) -> &'static isize {
    |                         +++++++
+help: instead, you are more likely to want to change the argument to be borrowed...
+   |
+LL | fn j(_x: &StaticStr) -> &isize {
+   |          +
+help: ...or alternatively, you might want to return an owned value
+   |
+LL - fn j(_x: StaticStr) -> &isize {
+LL + fn j(_x: StaticStr) -> isize {
+   |
 
 error[E0106]: missing lifetime specifier
   --> $DIR/lifetime-elision-return-type-requires-explicit-lifetime.rs:40:49

tests/ui/self/elision/nested-item.stderr

@@ -21,10 +21,19 @@ LL | fn wrap(self: Wrap<{ fn bar(&self) {} }>) -> &() {
    |                                              ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL | fn wrap(self: Wrap<{ fn bar(&self) {} }>) -> &'static () {
    |                                               +++++++
+help: instead, you are more likely to want to change the argument to be borrowed...
+   |
+LL | fn wrap(self: &Wrap<{ fn bar(&self) {} }>) -> &() {
+   |               +
+help: ...or alternatively, you might want to return an owned value
+   |
+LL - fn wrap(self: Wrap<{ fn bar(&self) {} }>) -> &() {
+LL + fn wrap(self: Wrap<{ fn bar(&self) {} }>) -> () {
+   |
 
 error[E0412]: cannot find type `Wrap` in this scope
   --> $DIR/nested-item.rs:5:15

tests/ui/suggestions/impl-trait-missing-lifetime-gated.stderr

@@ -5,10 +5,19 @@ LL |     fn g(mut x: impl Iterator<Item = &()>) -> Option<&()> { x.next() }
    |                                                      ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL |     fn g(mut x: impl Iterator<Item = &()>) -> Option<&'static ()> { x.next() }
    |                                                       +++++++
+help: consider introducing a named lifetime parameter
+   |
+LL |     fn g<'a>(mut x: impl Iterator<Item = &'a ()>) -> Option<&'a ()> { x.next() }
+   |         ++++                             ~~~                ~~~
+help: alternatively, you might want to return an owned value
+   |
+LL -     fn g(mut x: impl Iterator<Item = &()>) -> Option<&()> { x.next() }
+LL +     fn g(mut x: impl Iterator<Item = &()>) -> Option<()> { x.next() }
+   |
 
 error[E0106]: missing lifetime specifier
   --> $DIR/impl-trait-missing-lifetime-gated.rs:19:60
@@ -17,10 +26,19 @@ LL |     async fn i(mut x: impl Iterator<Item = &()>) -> Option<&()> { x.next()
    |                                                            ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL |     async fn i(mut x: impl Iterator<Item = &()>) -> Option<&'static ()> { x.next() }
    |                                                             +++++++
+help: consider introducing a named lifetime parameter
+   |
+LL |     async fn i<'a>(mut x: impl Iterator<Item = &'a ()>) -> Option<&'a ()> { x.next() }
+   |               ++++                             ~~~                ~~~
+help: alternatively, you might want to return an owned value
+   |
+LL -     async fn i(mut x: impl Iterator<Item = &()>) -> Option<&()> { x.next() }
+LL +     async fn i(mut x: impl Iterator<Item = &()>) -> Option<()> { x.next() }
+   |
 
 error[E0106]: missing lifetime specifier
   --> $DIR/impl-trait-missing-lifetime-gated.rs:27:58
@@ -29,10 +47,19 @@ LL |     fn g(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next()
    |                                                          ^^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`, or if you will only have owned values
    |
 LL |     fn g(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'static ()> { x.next() }
    |                                                          ~~~~~~~
+help: consider introducing a named lifetime parameter
+   |
+LL |     fn g<'a>(mut x: impl Iterator<Item = &'a ()>) -> Option<&'a ()> { x.next() }
+   |         ++++                             ~~~                ~~~
+help: alternatively, you might want to return an owned value
+   |
+LL -     fn g(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+LL +     fn g(mut x: impl Iterator<Item = &'_ ()>) -> Option<()> { x.next() }
+   |
 
 error[E0106]: missing lifetime specifier
   --> $DIR/impl-trait-missing-lifetime-gated.rs:37:64
@@ -41,10 +68,19 @@ LL |     async fn i(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.n
    |                                                                ^^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`, or if you will only have owned values
    |
 LL |     async fn i(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'static ()> { x.next() }
    |                                                                ~~~~~~~
+help: consider introducing a named lifetime parameter
+   |
+LL |     async fn i<'a>(mut x: impl Iterator<Item = &'a ()>) -> Option<&'a ()> { x.next() }
+   |               ++++                             ~~~                ~~~
+help: alternatively, you might want to return an owned value
+   |
+LL -     async fn i(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+LL +     async fn i(mut x: impl Iterator<Item = &'_ ()>) -> Option<()> { x.next() }
+   |
 
 error[E0106]: missing lifetime specifier
   --> $DIR/impl-trait-missing-lifetime-gated.rs:47:37
@@ -53,10 +89,19 @@ LL |     fn g(mut x: impl Foo) -> Option<&()> { x.next() }
    |                                     ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL |     fn g(mut x: impl Foo) -> Option<&'static ()> { x.next() }
    |                                      +++++++
+help: consider introducing a named lifetime parameter
+   |
+LL |     fn g<'a>(mut x: impl Foo) -> Option<&'a ()> { x.next() }
+   |         ++++                            ~~~
+help: alternatively, you might want to return an owned value
+   |
+LL -     fn g(mut x: impl Foo) -> Option<&()> { x.next() }
+LL +     fn g(mut x: impl Foo) -> Option<()> { x.next() }
+   |
 
 error[E0106]: missing lifetime specifier
   --> $DIR/impl-trait-missing-lifetime-gated.rs:58:41
@@ -65,10 +110,19 @@ LL |     fn g(mut x: impl Foo<()>) -> Option<&()> { x.next() }
    |                                         ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-help: consider using the `'static` lifetime
+help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`
    |
 LL |     fn g(mut x: impl Foo<()>) -> Option<&'static ()> { x.next() }
    |                                          +++++++
+help: consider introducing a named lifetime parameter
+   |
+LL |     fn g<'a>(mut x: impl Foo<()>) -> Option<&'a ()> { x.next() }
+   |         ++++                                ~~~
+help: alternatively, you might want to return an owned value
+   |
+LL -     fn g(mut x: impl Foo<()>) -> Option<&()> { x.next() }
+LL +     fn g(mut x: impl Foo<()>) -> Option<()> { x.next() }
+   |
 
 error[E0658]: anonymous lifetimes in `impl Trait` are unstable
   --> $DIR/impl-trait-missing-lifetime-gated.rs:6:35