sane indexing in text

crates/ra_assists/src/remove_dbg.rs

@@ -36,11 +36,10 @@ pub(crate) fn remove_dbg(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
 
     let macro_content = {
         let macro_args = macro_call.token_tree()?.syntax().clone();
-        let range = macro_args.range();
-        let start = range.start() + TextUnit::of_char('(');
-        let end = range.end() - TextUnit::of_char(')');
 
-        macro_args.text().slice(start..end).to_string()
+        let text = macro_args.text();
+        let without_parens = TextUnit::of_char('(')..text.len() - TextUnit::of_char(')');
+        text.slice(without_parens).to_string()
     };
 
     ctx.add_action(AssistId("remove_dbg"), "remove dbg!()", |edit| {

crates/ra_syntax/src/syntax_text.rs

@@ -95,18 +95,21 @@ impl<'a> SyntaxText<'a> {
         self.range.is_empty()
     }
 
-    /// NB, the offsets here are absolute, and this probably doesn't make sense!
     pub fn slice(&self, range: impl ops::RangeBounds<TextUnit>) -> SyntaxText<'a> {
         let start = match range.start_bound() {
-            Bound::Included(b) => *b,
+            Bound::Included(&b) => b,
-            Bound::Excluded(b) => *b + TextUnit::from(1u32),
+            Bound::Excluded(_) => panic!("utf-aware slicing can't work this way"),
-            Bound::Unbounded => self.range.start(),
+            Bound::Unbounded => 0.into(),
         };
         let end = match range.end_bound() {
-            Bound::Included(b) => *b + TextUnit::from(1u32),
+            Bound::Included(_) => panic!("utf-aware slicing can't work this way"),
-            Bound::Excluded(b) => *b,
+            Bound::Excluded(&b) => b,
-            Bound::Unbounded => self.range.end(),
+            Bound::Unbounded => self.len(),
         };
+        assert!(start <= end);
+        let len = end - start;
+        let start = self.range.start() + start;
+        let end = start + len;
         assert!(
             start <= end,
             "invalid slice, range: {:?}, slice: {:?}",