Optimise common => {{ macro pattern

Author: RReverser

src/bin/cargo-fmt.rs

@@ -97,14 +97,14 @@ fn execute() -> i32 {
 }
 
 macro_rules! print_usage {
-    ($print: ident, $opts: ident, $reason: expr) => ({
+    ($print: ident, $opts: ident, $reason: expr) => {{
         let msg = format!("{}\nusage: cargo fmt [options]", $reason);
         $print!(
             "{}\nThis utility formats all bin and lib files of the current crate using rustfmt. \
              Arguments after `--` are passed to rustfmt.",
             $opts.usage(&msg)
         );
-    })
+    }};
 }
 
 fn print_usage_to_stdout(opts: &Options, reason: &str) {

src/macros.rs

@@ -335,8 +335,6 @@ pub fn rewrite_macro_def(
             result += &args;
         }
 
-        result += " {\n";
-
         // The macro body is the most interesting part. It might end up as various
         // AST nodes, but also has special variables (e.g, `$foo`) which can't be
         // parsed as regular Rust code (and note that these can be escaped using
@@ -346,13 +344,23 @@ pub fn rewrite_macro_def(
         let old_body = context.snippet(branch.body).trim();
         let (body_str, substs) = replace_names(old_body);
 
-        // We'll hack the indent below, take this into account when formatting,
         let mut config = context.config.clone();
-        let body_indent = mac_indent.block_indent(&config);
-        let new_width = config.max_width() - body_indent.width();
-        config.set().max_width(new_width);
         config.set().hide_parse_errors(true);
 
+        result += " {";
+
+        let has_block_body = old_body.starts_with("{");
+
+        let body_indent = if has_block_body {
+            mac_indent
+        } else {
+            // We'll hack the indent below, take this into account when formatting,
+            let body_indent = mac_indent.block_indent(&config);
+            let new_width = config.max_width() - body_indent.width();
+            config.set().max_width(new_width);
+            body_indent
+        };
+
         // First try to format as items, then as statements.
         let new_body = match ::format_snippet(&body_str, &config) {
             Some(new_body) => new_body,
@@ -387,9 +395,14 @@ pub fn rewrite_macro_def(
             new_body = new_body.replace(new, old);
         }
 
-        result += &new_body;
+        if has_block_body {
+            result += new_body.trim();
+        } else {
+            result += "\n";
+            result += &new_body;
+            result += &mac_indent_str;
+        }
 
-        result += &mac_indent_str;
         result += "}";
         if def.legacy {
             result += ";";

tests/target/macro_rules.rs

@@ -1,10 +1,8 @@
 macro_rules! m {
-    ($expr: expr, $func: ident) => {
-        {
-            let x = $expr;
-            $func(x)
-        }
-    };
+    ($expr: expr, $func: ident) => {{
+        let x = $expr;
+        $func(x)
+    }};
 
     () => {
     };