Add trim_tries

src/chains.rs

@@ -65,7 +65,7 @@
 //!            .qux
 //! ```
 
-use comment::rewrite_comment;
+use comment::{rewrite_comment, CharClasses, FullCodeCharKind, RichChar};
 use config::IndentStyle;
 use expr::rewrite_call;
 use lists::{extract_post_comment, extract_pre_comment, get_comment_end};
@@ -870,3 +870,28 @@ fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool
         _ => false,
     }
 }
+
+/// Remove try operators (`?`s) that appear in the given string. If removing
+/// them leaves an empty line, remove that line as well unless it is the first
+/// line (we need the first newline for detecting pre/post comment).
+fn trim_tries(s: &str) -> String {
+    let mut result = String::with_capacity(s.len());
+    let mut line_buffer = String::with_capacity(s.len());
+    for (kind, rich_char) in CharClasses::new(s.chars()) {
+        match rich_char.get_char() {
+            '\n' => {
+                if result.is_empty() || !line_buffer.trim().is_empty() {
+                    result.push_str(&line_buffer);
+                    result.push('\n')
+                }
+                line_buffer.clear();
+            }
+            '?' if kind == FullCodeCharKind::Normal => continue,
+            c => line_buffer.push(c),
+        }
+    }
+    if !line_buffer.trim().is_empty() {
+        result.push_str(&line_buffer);
+    }
+    result
+}