From c6845524ce8aa7ea99b68c98fb0e1acf43b21e87 Mon Sep 17 00:00:00 2001
From: Kendall Condon <goon.pri.low@gmail.com>
Date: Mon, 28 Jul 2025 16:39:20 -0400
Subject: [PATCH] zig fmt: fix doc comments on fn paramaters without comma

---
 lib/std/zig/Ast/Render.zig  | 29 ++++++++++++++++++++------
 lib/std/zig/parser_test.zig | 41 +++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 6 deletions(-)

diff --git a/lib/std/zig/Ast/Render.zig b/lib/std/zig/Ast/Render.zig
index 6752da2ae4..ccbaba1469 100644
--- a/lib/std/zig/Ast/Render.zig
+++ b/lib/std/zig/Ast/Render.zig
@@ -1617,6 +1617,27 @@ fn renderBuiltinCall(
     return renderParamList(r, builtin_token + 1, params, space);
 }
 
+fn isOneLineFnProto(
+    tree: Ast,
+    fn_proto: Ast.full.FnProto,
+    lparen: Ast.TokenIndex,
+    rparen: Ast.TokenIndex,
+) bool {
+    const trailing_comma = tree.tokenTag(rparen - 1) == .comma;
+    if (trailing_comma or hasComment(tree, lparen, rparen))
+        return false;
+
+    // Check that there are no doc comments
+    var after_last_param = lparen + 1;
+    for (fn_proto.ast.params) |expr| {
+        // Looking before each param is insufficient since anytype is not included in `params`
+        if (hasDocComment(tree, after_last_param, tree.firstToken(expr)))
+            return false;
+        after_last_param = tree.lastToken(expr) + 1;
+    }
+    return !hasDocComment(tree, after_last_param, rparen);
+}
+
 fn renderFnProto(r: *Render, fn_proto: Ast.full.FnProto, space: Space) Error!void {
     const tree = r.tree;
     const ais = r.ais;
@@ -1677,8 +1698,7 @@ fn renderFnProto(r: *Render, fn_proto: Ast.full.FnProto, space: Space) Error!voi
 
     // The params list is a sparse set that does *not* include anytype or ... parameters.
 
-    const trailing_comma = tree.tokenTag(rparen - 1) == .comma;
-    if (!trailing_comma and !hasComment(tree, lparen, rparen)) {
+    if (isOneLineFnProto(tree, fn_proto, lparen, rparen)) {
         // Render all on one line, no trailing comma.
         try renderToken(r, lparen, .none); // (
 
@@ -1687,10 +1707,7 @@ fn renderFnProto(r: *Render, fn_proto: Ast.full.FnProto, space: Space) Error!voi
         while (true) {
             last_param_token += 1;
             switch (tree.tokenTag(last_param_token)) {
-                .doc_comment => {
-                    try renderToken(r, last_param_token, .newline);
-                    continue;
-                },
+                .doc_comment => unreachable,
                 .ellipsis3 => {
                     try renderToken(r, last_param_token, .none); // ...
                     break;
diff --git a/lib/std/zig/parser_test.zig b/lib/std/zig/parser_test.zig
index f7b6d3ed2d..676ea0b03c 100644
--- a/lib/std/zig/parser_test.zig
+++ b/lib/std/zig/parser_test.zig
@@ -6448,6 +6448,47 @@ test "zig fmt: whitespace with multiline strings" {
     );
 }
 
+test "zig fmt: doc comments on fn parameters" {
+    try testTransform(
+        \\extern fn foo(
+        \\    /// Bitmap
+        \\    active: u64
+        \\) void;
+        \\extern fn bar(
+        \\    bits: u6,
+        \\    /// Bitmap
+        \\    active: u64
+        \\) void;
+        \\extern fn baz(
+        \\    /// Bitmap
+        \\    active: anytype
+        \\) void;
+        \\
+    ,
+        \\extern fn foo(
+        \\    /// Bitmap
+        \\    active: u64,
+        \\) void;
+        \\extern fn bar(
+        \\    bits: u6,
+        \\    /// Bitmap
+        \\    active: u64,
+        \\) void;
+        \\extern fn baz(
+        \\    /// Bitmap
+        \\    active: anytype,
+        \\) void;
+        \\
+    );
+    try testCanonical(
+        \\extern fn foo(x: struct {
+        \\    /// Bitmap
+        \\    active: u64,
+        \\}) void;
+        \\
+    );
+}
+
 test "recovery: top level" {
     try testError(
         \\test "" {inline}