From 11a4ce42c16c17422cd272f154c9c33231bcc61a Mon Sep 17 00:00:00 2001
From: LemonBoy <thatlemon@gmail.com>
Date: Fri, 28 Feb 2020 12:06:43 +0100
Subject: [PATCH] zig fmt: Respect trailing commas in error set declarations

The logic is not perfect as it doesn't take into account the presence of
doc comments, but it's an improvement over the status quo.
---
 lib/std/zig/parser_test.zig |  2 ++
 lib/std/zig/render.zig      | 58 ++++++++++++++++++++++++++-----------
 2 files changed, 43 insertions(+), 17 deletions(-)

diff --git a/lib/std/zig/parser_test.zig b/lib/std/zig/parser_test.zig
index d00568e49..e1fe07a57 100644
--- a/lib/std/zig/parser_test.zig
+++ b/lib/std/zig/parser_test.zig
@@ -1509,6 +1509,8 @@ test "zig fmt: error set declaration" {
         \\const Error = error{OutOfMemory};
         \\const Error = error{};
         \\
+        \\const Error = error{ OutOfMemory, OutOfTime };
+        \\
     );
 }
 
diff --git a/lib/std/zig/render.zig b/lib/std/zig/render.zig
index a3a72fb23..23dc9e02a 100644
--- a/lib/std/zig/render.zig
+++ b/lib/std/zig/render.zig
@@ -1268,25 +1268,51 @@ fn renderExpression(
             }
 
             try renderToken(tree, stream, err_set_decl.error_token, indent, start_col, Space.None); // error
-            try renderToken(tree, stream, lbrace, indent, start_col, Space.Newline); // {
-            const new_indent = indent + indent_delta;
 
-            var it = err_set_decl.decls.iterator(0);
-            while (it.next()) |node| {
-                try stream.writeByteNTimes(' ', new_indent);
+            const src_has_trailing_comma = blk: {
+                const maybe_comma = tree.prevToken(err_set_decl.rbrace_token);
+                break :blk tree.tokens.at(maybe_comma).id == .Comma;
+            };
 
-                if (it.peek()) |next_node| {
-                    try renderExpression(allocator, stream, tree, new_indent, start_col, node.*, Space.None);
-                    try renderToken(tree, stream, tree.nextToken(node.*.lastToken()), new_indent, start_col, Space.Newline); // ,
+            if (src_has_trailing_comma) {
+                try renderToken(tree, stream, lbrace, indent, start_col, Space.Newline); // {
+                const new_indent = indent + indent_delta;
 
-                    try renderExtraNewline(tree, stream, start_col, next_node.*);
-                } else {
-                    try renderExpression(allocator, stream, tree, new_indent, start_col, node.*, Space.Comma);
+                var it = err_set_decl.decls.iterator(0);
+                while (it.next()) |node| {
+                    try stream.writeByteNTimes(' ', new_indent);
+
+                    if (it.peek()) |next_node| {
+                        try renderExpression(allocator, stream, tree, new_indent, start_col, node.*, Space.None);
+                        try renderToken(tree, stream, tree.nextToken(node.*.lastToken()), new_indent, start_col, Space.Newline); // ,
+
+                        try renderExtraNewline(tree, stream, start_col, next_node.*);
+                    } else {
+                        try renderExpression(allocator, stream, tree, new_indent, start_col, node.*, Space.Comma);
+                    }
                 }
-            }
 
-            try stream.writeByteNTimes(' ', indent);
-            return renderToken(tree, stream, err_set_decl.rbrace_token, indent, start_col, space); // }
+                try stream.writeByteNTimes(' ', indent);
+                return renderToken(tree, stream, err_set_decl.rbrace_token, indent, start_col, space); // }
+            } else {
+                try renderToken(tree, stream, lbrace, indent, start_col, Space.Space); // {
+
+                var it = err_set_decl.decls.iterator(0);
+                while (it.next()) |node| {
+                    if (it.peek()) |next_node| {
+                        try renderExpression(allocator, stream, tree, indent, start_col, node.*, Space.None);
+
+                        const comma_token = tree.nextToken(node.*.lastToken());
+                        assert(tree.tokens.at(comma_token).id == .Comma);
+                        try renderToken(tree, stream, comma_token, indent, start_col, Space.Space); // ,
+                        try renderExtraNewline(tree, stream, start_col, next_node.*);
+                    } else {
+                        try renderExpression(allocator, stream, tree, indent, start_col, node.*, Space.Space);
+                    }
+                }
+
+                return renderToken(tree, stream, err_set_decl.rbrace_token, indent, start_col, space); // }
+            }
         },
 
         .ErrorTag => {
@@ -1589,8 +1615,7 @@ fn renderExpression(
                 }
             } else {
                 var it = switch_case.items.iterator(0);
-                while (true) {
-                    const node = it.next().?;
+                while (it.next()) |node| {
                     if (it.peek()) |next_node| {
                         try renderExpression(allocator, stream, tree, indent, start_col, node.*, Space.None);
 
@@ -1601,7 +1626,6 @@ fn renderExpression(
                     } else {
                         try renderExpression(allocator, stream, tree, indent, start_col, node.*, Space.Comma);
                         try stream.writeByteNTimes(' ', indent);
-                        break;
                     }
                 }
             }