Add known bug test.

src/test/ui/lifetimes/bare-trait-object-borrowck.rs

@@ -0,0 +1,27 @@
+#![allow(bare_trait_objects)]
+
+pub struct FormatWith<'a, I, F> {
+    sep: &'a str,
+    /// FormatWith uses interior mutability because Display::fmt takes &self.
+    inner: RefCell<Option<(I, F)>>,
+}
+
+use std::cell::RefCell;
+use std::fmt;
+
+struct Layout;
+
+pub fn new_format<'a, I, F>(iter: I, separator: &'a str, f: F) -> FormatWith<'a, I, F>
+where
+    I: Iterator,
+    F: FnMut(I::Item, &mut FnMut(&fmt::Display) -> fmt::Result) -> fmt::Result,
+{
+    FormatWith { sep: separator, inner: RefCell::new(Some((iter, f))) }
+}
+
+fn main() {
+    let _ = new_format(0..32, " | ", |i, f| f(&format_args!("0x{:x}", i)));
+    //~^ ERROR temporary value dropped while borrowed
+    //~| ERROR temporary value dropped while borrowed
+    //~| ERROR `i` does not live long enough
+}

src/test/ui/lifetimes/bare-trait-object-borrowck.stderr

@@ -0,0 +1,43 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/bare-trait-object-borrowck.rs:23:48
+   |
+LL |     let _ = new_format(0..32, " | ", |i, f| f(&format_args!("0x{:x}", i)));
+   |                                          -  ---^^^^^^^^^^^^^^^^^^^^^^^^^-
+   |                                          |  |  |                        |
+   |                                          |  |  |                        temporary value is freed at the end of this statement
+   |                                          |  |  creates a temporary which is freed while still in use
+   |                                          |  argument requires that borrow lasts for `'1`
+   |                                          has type `&mut dyn FnMut(&'1 (dyn std::fmt::Display + '1)) -> Result<(), std::fmt::Error>`
+   |
+   = note: this error originates in the macro `format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/bare-trait-object-borrowck.rs:23:48
+   |
+LL |     let _ = new_format(0..32, " | ", |i, f| f(&format_args!("0x{:x}", i)));
+   |                                          -  ---^^^^^^^^^^^^^^^^^^^^^^^^^-
+   |                                          |  |  |                        |
+   |                                          |  |  |                        temporary value is freed at the end of this statement
+   |                                          |  |  creates a temporary which is freed while still in use
+   |                                          |  argument requires that borrow lasts for `'1`
+   |                                          has type `&mut dyn FnMut(&'1 (dyn std::fmt::Display + '1)) -> Result<(), std::fmt::Error>`
+   |
+   = note: this error originates in the macro `format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0597]: `i` does not live long enough
+  --> $DIR/bare-trait-object-borrowck.rs:23:71
+   |
+LL |     let _ = new_format(0..32, " | ", |i, f| f(&format_args!("0x{:x}", i)));
+   |                                          -  --------------------------^--
+   |                                          |  |                         | |
+   |                                          |  |                         | `i` dropped here while still borrowed
+   |                                          |  |                         borrowed value does not live long enough
+   |                                          |  argument requires that `i` is borrowed for `'1`
+   |                                          has type `&mut dyn FnMut(&'1 (dyn std::fmt::Display + '1)) -> Result<(), std::fmt::Error>`
+   |
+   = note: this error originates in the macro `format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0597, E0716.
+For more information about an error, try `rustc --explain E0597`.

src/test/ui/lifetimes/bare-trait-object.rs

@@ -0,0 +1,27 @@
+// Verify that lifetime resolution correctly accounts for `Fn` bare trait objects.
+
+#![allow(bare_trait_objects)]
+
+// This should work as: fn next_u32(fill_buf: &mut dyn FnMut(&mut [u8]))
+fn next_u32(fill_buf: &mut FnMut(&mut [u8])) {
+    let mut buf: [u8; 4] = [0; 4];
+    fill_buf(&mut buf);
+}
+
+fn explicit(fill_buf: &mut dyn FnMut(&mut [u8])) {
+    let mut buf: [u8; 4] = [0; 4];
+    fill_buf(&mut buf);
+}
+
+fn main() {
+    let _: fn(&mut FnMut(&mut [u8])) = next_u32;
+    //~^ ERROR mismatched types
+    let _: &dyn Fn(&mut FnMut(&mut [u8])) = &next_u32;
+    let _: fn(&mut FnMut(&mut [u8])) = explicit;
+    //~^ ERROR mismatched types
+    let _: &dyn Fn(&mut FnMut(&mut [u8])) = &explicit;
+    let _: fn(&mut dyn FnMut(&mut [u8])) = next_u32;
+    let _: &dyn Fn(&mut dyn FnMut(&mut [u8])) = &next_u32;
+    let _: fn(&mut dyn FnMut(&mut [u8])) = explicit;
+    let _: &dyn Fn(&mut dyn FnMut(&mut [u8])) = &explicit;
+}

src/test/ui/lifetimes/bare-trait-object.stderr

@@ -0,0 +1,21 @@
+error[E0308]: mismatched types
+  --> $DIR/bare-trait-object.rs:17:40
+   |
+LL |     let _: fn(&mut FnMut(&mut [u8])) = next_u32;
+   |                                        ^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r, 's> fn(&'r mut (dyn for<'s> FnMut(&'s mut [u8]) + 'r))`
+                 found fn item `for<'r> fn(&'r mut (dyn for<'r> FnMut(&'r mut [u8]) + 'r)) {next_u32}`
+
+error[E0308]: mismatched types
+  --> $DIR/bare-trait-object.rs:20:40
+   |
+LL |     let _: fn(&mut FnMut(&mut [u8])) = explicit;
+   |                                        ^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r, 's> fn(&'r mut (dyn for<'s> FnMut(&'s mut [u8]) + 'r))`
+                 found fn item `for<'r> fn(&'r mut (dyn for<'r> FnMut(&'r mut [u8]) + 'r)) {explicit}`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.