Merge pull request #663 from SingingTree/match_trailing_comma

WIP: Trailing commas for match block arms

src/config.rs

@@ -308,4 +308,6 @@ create_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)";
 }

src/expr.rs

@@ -20,7 +20,7 @@ use string::{StringFormat, rewrite_string};
 use utils::{span_after, extra_offset, last_line_width, wrap_str, binary_search, first_line_width,
             semicolon_for_stmt};
 use visitor::FmtVisitor;
-use config::{StructLitStyle, MultilineStyle};
+use config::{Config, StructLitStyle, MultilineStyle};
 use comment::{FindUncommented, rewrite_comment, contains_comment};
 use types::rewrite_path;
 use items::{span_lo_for_arg, span_hi_for_arg};
@@ -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.config, &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(config: &Config, body: &ast::Expr) -> &'static str {
+    if 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 @@ impl Rewrite for ast::Arm {
             ref x => x,
         };
 
-        let comma = arm_comma(body);
+        let comma = arm_comma(&context.config, body);
 
         // Let's try and get the arm body on the same line as the condition.
         // 4 = ` => `.len()
@@ -958,10 +960,15 @@ impl Rewrite for ast::Arm {
             let budget = context.config.max_width - line_start - comma.len() - 4;
             let offset = Indent::new(offset.block_indent, line_start + 4 - offset.block_indent);
             let rewrite = nop_block_collapse(body.rewrite(context, budget, offset), budget);
+            let is_block = if let ast::ExprBlock(ref block) = body.node {
+                true
+            } else {
+                false
+            };
 
             match rewrite {
                 Some(ref body_str) if !body_str.contains('\n') || !context.config.wrap_match_arms ||
-                                      comma.is_empty() => {
+                                      is_block => {
                     return Some(format!("{}{} => {}{}",
                                         attr_str.trim_left(),
                                         pats_str,
@@ -983,7 +990,11 @@ impl Rewrite for ast::Arm {
                                                          body_budget));
         let indent_str = offset.block_indent(context.config).to_string(context.config);
         let (body_prefix, body_suffix) = if context.config.wrap_match_arms {
-            (" {", "}")
+            if context.config.match_block_trailing_comma {
+                (" {", "},")
+            } else {
+                (" {", "}")
+            }
         } else {
             ("", "")
         };

tests/source/match-block-trailing-comma.rs

@@ -0,0 +1,14 @@
+// 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 => (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa,
+              bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb),
+    }
+}

tests/source/match-nowrap-trailing-comma.rs

@@ -0,0 +1,15 @@
+// rustfmt-wrap_match_arms: false
+// 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 => (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa,
+              bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb),
+    }
+}

tests/target/match-block-trailing-comma.rs

@@ -0,0 +1,16 @@
+// 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 => {
+            (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa,
+             bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb)
+        },
+    }
+}

tests/target/match-nowrap-trailing-comma.rs

@@ -0,0 +1,15 @@
+// rustfmt-wrap_match_arms: false
+// 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 => (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa,
+              bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb),
+    }
+}