use pretty_print_const_value from MIR constant 'extra' printing

compiler/rustc_data_structures/src/lib.rs

@@ -47,6 +47,8 @@ extern crate cfg_if;
 #[macro_use]
 extern crate rustc_macros;
 
+use std::fmt;
+
 pub use rustc_index::static_assert_size;
 
 #[inline(never)]
@@ -126,6 +128,23 @@ impl<F: FnOnce()> Drop for OnDrop<F> {
     }
 }
 
+/// Turns a closure that takes an `&mut Formatter` into something that can be display-formatted.
+pub fn make_display(f: impl Fn(&mut fmt::Formatter<'_>) -> fmt::Result) -> impl fmt::Display {
+    struct Printer<F> {
+        f: F,
+    }
+    impl<F> fmt::Display for Printer<F>
+    where
+        F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result,
+    {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            (self.f)(fmt)
+        }
+    }
+
+    Printer { f }
+}
+
 // See comments in src/librustc_middle/lib.rs
 #[doc(hidden)]
 pub fn __noop_fix_for_27438() {}