Trailing commas for match block arms

Attempt to implement an option for trailing commas for block based match arms (issue
173). Put in place test files to verify this behaviour.

diff --git a/src/config.rs b/src/config.rs
index c02d618437fa3620648a893630191b0babf2ccfe..2ea175c385f308fd6bbc6487492285a30af20f32 100644 (file)
--- a/src/config.rs
+++ b/src/config.rs
@@ -308,4 +308,6 @@ fn default() -> Config {
     hard_tabs: bool, false, "Use tab characters for indentation, spaces for alignment";
     wrap_comments: bool, false, "Break comments to fit on the line";
     wrap_match_arms: bool, true, "Wrap multiline match arms in blocks";
+    match_block_trailing_comma: bool, false,
+        "Put a trailing comma after a block based match arm (non-block arms are not affected)";
 }

diff --git a/src/expr.rs b/src/expr.rs
index 040c83488a72ed375a63e768366e495b24ef30e2..9338160d98fdc3f283bf81dec9fd9722de7d4e9a 100644 (file)
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -823,7 +823,7 @@ fn rewrite_match(context: &RewriteContext,
             // We couldn't format the arm, just reproduce the source.
             let snippet = context.snippet(mk_sp(arm_start_pos(arm), arm_end_pos(arm)));
             result.push_str(&snippet);
-            result.push_str(arm_comma(&arm.body));
+            result.push_str(arm_comma(context, &arm.body));
         }
     }
     // BytePos(1) = closing match brace.
@@ -854,8 +854,10 @@ fn arm_end_pos(arm: &ast::Arm) -> BytePos {
     arm.body.span.hi
 }
 
-fn arm_comma(body: &ast::Expr) -> &'static str {
-    if let ast::ExprBlock(ref block) = body.node {
+fn arm_comma(context: &RewriteContext, body: &ast::Expr) -> &'static str {
+    if context.config.match_block_trailing_comma {
+        ","
+    } else if let ast::ExprBlock(ref block) = body.node {
         if let ast::DefaultBlock = block.rules {
             ""
         } else {
@@ -950,7 +952,7 @@ fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Opt
             ref x => x,
         };
 
-        let comma = arm_comma(body);
+        let comma = arm_comma(context, body);
 
         // Let's try and get the arm body on the same line as the condition.
         // 4 = ` => `.len()
@@ -961,7 +963,8 @@ fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Opt
 
             match rewrite {
                 Some(ref body_str) if !body_str.contains('\n') || !context.config.wrap_match_arms ||
-                                      comma.is_empty() => {
+                                      comma.is_empty() ||
+                                      context.config.match_block_trailing_comma => {
                     return Some(format!("{}{} => {}{}",
                                         attr_str.trim_left(),
                                         pats_str,

diff --git a/tests/source/match-block-trailing-comma.rs b/tests/source/match-block-trailing-comma.rs
new file mode 100644 (file)
index 0000000..7f7ddd0
--- /dev/null
+++ b/tests/source/match-block-trailing-comma.rs
@@ -0,0 +1,13 @@
+// rustfmt-match_block_trailing_comma: true
+// Match expressions, no unwrapping of block arms or wrapping of multiline
+// expressions.
+
+fn foo() {
+    match x {
+        a => {
+            "line1";
+            "line2"
+        }
+        b => "bar",
+    }
+}

diff --git a/tests/target/match-block-trailing-comma.rs b/tests/target/match-block-trailing-comma.rs
new file mode 100644 (file)
index 0000000..c845bae
--- /dev/null
+++ b/tests/target/match-block-trailing-comma.rs
@@ -0,0 +1,13 @@
+// rustfmt-match_block_trailing_comma: true
+// Match expressions, no unwrapping of block arms or wrapping of multiline
+// expressions.
+
+fn foo() {
+    match x {
+        a => {
+            "line1";
+            "line2"
+        },
+        b => "bar",
+    }
+}