syntax: improve Debug impl for IntervalSet

This shows up in the Debug representation of an HIR. This impl removes a
layer of indirection in the output and drops internal optimization
fields like 'folded'.

Author: BurntSushi

regex-syntax/src/hir/interval.rs

@@ -30,7 +30,7 @@ use crate::unicode;
 //
 // Tests on this are relegated to the public API of HIR in src/hir.rs.
 
-#[derive(Clone, Debug)]
+#[derive(Clone)]
 pub struct IntervalSet<I> {
     /// A sorted set of non-overlapping ranges.
     ranges: Vec<I>,
@@ -64,6 +64,16 @@ impl<I: Interval> PartialEq for IntervalSet<I> {
     }
 }
 
+impl<I: core::fmt::Debug> core::fmt::Debug for IntervalSet<I> {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        let mut fmter = f.debug_tuple("IntervalSet");
+        for range in self.ranges.iter() {
+            fmter.field(range);
+        }
+        fmter.finish()
+    }
+}
+
 impl<I: Interval> IntervalSet<I> {
     /// Create a new set from a sequence of intervals. Each interval is
     /// specified as a pair of bounds, where both bounds are inclusive.