don't print self symbol's internal index unless gensymed

It's just not useful. It also makes it hard to have tests that probe
internal state, since the interning number is very sensitive.

Dumping the number in the case of gensym is not ideal but will do for
now.

1 files changed, 10 insertions, 1 deletions

diff --git a/src/libsyntax_pos/symbol.rs b/src/libsyntax_pos/symbol.rs
index 69ddd560213..72760360711 100644
--- a/src/libsyntax_pos/symbol.rs
+++ b/src/libsyntax_pos/symbol.rs
@@ -123,7 +123,12 @@ impl<'a> From<&'a str> for Symbol {
 
 impl fmt::Debug for Symbol {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}({})", self, self.0)
+        let is_gensymed = with_interner(|interner| interner.is_gensymed(*self));
+        if is_gensymed {
+            write!(f, "{}({})", self, self.0)
+        } else {
+            write!(f, "{}", self)
+        }
     }
 }
 
@@ -201,6 +206,10 @@ impl Interner {
         Symbol(!0 - self.gensyms.len() as u32 + 1)
     }
 
+    fn is_gensymed(&mut self, symbol: Symbol) -> bool {
+        symbol.0 as usize >= self.strings.len()
+    }
+
     pub fn get(&self, symbol: Symbol) -> &str {
         match self.strings.get(symbol.0 as usize) {
             Some(ref string) => string,