fmt: automatically remove self-closing slash from void elements

kristoff-it · kristoff-it · commit 2bf8f4db4f91 · 2025-09-16T23:11:00.000+02:00
Non-void elements will not be automatically fixed and the error will
remain for the user to see. One reason for this behavior is to make
sure we don't "sneakily" remove a self-closing tag from an element that
was hiding a nesting error. By having the user face the problem they
get a chance to discover the latent mistake and fix it, on top of
learning a bit more about html.

This is what I mean by latent nesting bug:

```
&lt;body&gt;
  &lt;div /&gt;
  &lt;div&gt;
&lt;/body&gt;
```
The indentation of this code seems to suggest that the two divs are
sibling, while in reality the second one is a child of the first because
in HTML self-closing slashes are ignored.

As of today editors like VSCode will produce misleading indentation
in the presence of a self-closing slash, helping perpetuate mistakes.
diff --git a/src/html/Ast.zig b/src/html/Ast.zig
@@ -1303,7 +1303,7 @@ pub fn render(ast: Ast, src: []const u8, w: *Writer) !void {
                         }
                     }
 
-                    if (current.self_closing) {
+                    if (current.self_closing and !current.kind.isVoid()) {
                         try w.print("/", .{});
                     }
                     try w.print(">", .{});

Original file line number	Diff line number	Diff line change
`@@ -1303,7 +1303,7 @@ pub fn render(ast: Ast, src: []const u8, w: *Writer) !void {`
`1303`	`1303`	`}`
`1304`	`1304`	`}`
`1305`	`1305`
`1306`		`- if (current.self_closing) {`
	`1306`	`+ if (current.self_closing and !current.kind.isVoid()) {`
`1307`	`1307`	`try w.print("/", .{});`
`1308`	`1308`	`}`
`1309`	`1309`	`try w.print(">", .{});`