Rollup merge of #22901 - thepowersgang:patch-1, r=eddyb

A misplaced uint->u32 instead of usize in fmt::Pointer. Added a basic test.

src/test/run-pass/ifmt.rs

@@ -137,6 +137,13 @@ pub fn main() {
     t!(format!("{:+10.3e}", 1.2345e6f64),  "  +1.234e6");
     t!(format!("{:+10.3e}", -1.2345e6f64), "  -1.234e6");
 
+    // Test that pointers don't get truncated.
+    {
+        let val = usize::MAX;
+        let exp = format!("{:#x}", val);
+        t!(format!("{:p}", val as *const isize), exp);
+    }
+
     // Escaping
     t!(format!("{{"), "{");
     t!(format!("}}"), "}");