Account for use of index-based lifetime names in print of binder

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -2173,10 +2173,16 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
 
         let mut region_index = self.region_index;
         let mut next_name = |this: &Self| {
-            let name = name_by_region_index(region_index, &mut available_names, num_available);
-            debug!(?name);
-            region_index += 1;
-            assert!(!this.used_region_names.contains(&name));
+            let mut name;
+
+            loop {
+                name = name_by_region_index(region_index, &mut available_names, num_available);
+                region_index += 1;
+
+                if !this.used_region_names.contains(&name) {
+                    break;
+                }
+            }
 
             name
         };

src/test/ui/regions/issue-102374.rs

@@ -0,0 +1,20 @@
+use std::cell::Cell;
+
+#[rustfmt::skip]
+fn f(
+    f: for<'a, 'b, 'c, 'd, 'e, 'f, 'g,
+           'h, 'i, 'j, 'k, 'l, 'm, 'n,
+           'o, 'p, 'q, 'r, 's, 't, 'u,
+           'v, 'w, 'x, 'y, 'z, 'z0>
+        fn(Cell<(&   i32, &'a i32, &'b i32, &'c i32, &'d i32,
+                 &'e i32, &'f i32, &'g i32, &'h i32, &'i i32,
+                 &'j i32, &'k i32, &'l i32, &'m i32, &'n i32,
+                 &'o i32, &'p i32, &'q i32, &'r i32, &'s i32,
+                 &'t i32, &'u i32, &'v i32, &'w i32, &'x i32,
+                 &'y i32, &'z i32, &'z0 i32)>),
+) -> i32 {
+    f
+    //~^ ERROR mismatched types
+}
+
+fn main() {}

src/test/ui/regions/issue-102374.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-102374.rs:16:5
+   |
+LL | ) -> i32 {
+   |      --- expected `i32` because of return type
+LL |     f
+   |     ^ expected `i32`, found fn pointer
+   |
+   = note:    expected type `i32`
+           found fn pointer `for<'z1, 'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, 'j, 'k, 'l, 'm, 'n, 'o, 'p, 'q, 'r, 's, 't, 'u, 'v, 'w, 'x, 'y, 'z, 'z0> fn(Cell<(&'z1 i32, &'a i32, &'b i32, &'c i32, &'d i32, &'e i32, &'f i32, &'g i32, &'h i32, &'i i32, &'j i32, &'k i32, &'l i32, &'m i32, &'n i32, &'o i32, &'p i32, &'q i32, &'r i32, &'s i32, &'t i32, &'u i32, &'v i32, &'w i32, &'x i32, &'y i32, &'z i32, &'z0 i32)>)`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.