Improve handling of commas after match arms.

Fixes #507. Fixes #508.

src/expr.rs

@@ -779,6 +779,7 @@ 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));
         }
     }
     // BytePos(1) = closing match brace.
@@ -809,6 +810,18 @@ 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 {
+        if let ast::DefaultBlock = block.rules {
+            ""
+        } else {
+            ","
+        }
+    } else {
+        ","
+    }
+}
+
 // Match arms.
 impl Rewrite for ast::Arm {
     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
@@ -881,11 +894,7 @@ impl Rewrite for ast::Arm {
             line_start += offset.width();
         }
 
-        let comma = if let ast::ExprBlock(_) = body.node {
-            ""
-        } else {
-            ","
-        };
+        let comma = arm_comma(body);
 
         // Let's try and get the arm body on the same line as the condition.
         // 4 = ` => `.len()

tests/source/match.rs

@@ -226,3 +226,20 @@ fn issue280() {
 fn issue383() {
     match resolution.last_private {LastImport{..} => false, _ => true};
 }
+
+fn issue507() {
+    match 1 {
+        1 => unsafe { std::intrinsics::abort() },
+        _ => (),
+    }
+}
+
+fn issue508() {
+    match s.type_id() {
+        Some(NodeTypeId::Element(ElementTypeId::HTMLElement(
+                    HTMLElementTypeId::HTMLCanvasElement))) => true,
+        Some(NodeTypeId::Element(ElementTypeId::HTMLElement(
+                        HTMLElementTypeId::HTMLObjectElement))) => s.has_object_data(),
+        Some(NodeTypeId::Element(_)) => false,
+    }
+}

tests/target/match.rs

@@ -230,3 +230,20 @@ fn issue383() {
         _ => true,
     }
 }
+
+fn issue507() {
+    match 1 {
+        1 => unsafe { std::intrinsics::abort() },
+        _ => (),
+    }
+}
+
+fn issue508() {
+    match s.type_id() {
+        Some(NodeTypeId::Element(ElementTypeId::HTMLElement(
+                    HTMLElementTypeId::HTMLCanvasElement))) => true,
+        Some(NodeTypeId::Element(ElementTypeId::HTMLElement(
+                        HTMLElementTypeId::HTMLObjectElement))) => s.has_object_data(),
+        Some(NodeTypeId::Element(_)) => false,
+    }
+}