fix: formatting macro with braces delimiter by dswij · Pull Request #7031 · rust-lang/rustfmt

dswij · 2026-08-16T13:08:08Z

This PR makes it so that trim_left_preserve_layout does nothing when the first line contains a string start.

e.g., this will now not be formatted

macro! {"
...
"};

I'm not too satisfied with this PR; I think the formatting for macros with braces {,} needs to be reworked. I'm opening this PR as a starting point for that goal.

ytmimi · 2026-08-19T00:37:49Z

@rustbot author

ytmimi

Need to revert unnecessary changes

View changes since this review

ytmimi

Thanks for continuing to look at this. Here's my next round of review.

View changes since this review

ytmimi · 2026-09-02T23:22:50Z

@@ -615,43 +607,73 @@
    buffer
 }

-/// Indent each line according to the specified `indent`.
+/// Similar to `[::trim_left_preserve_layout]` but for macros.
+pub(crate) fn trim_left_preserve_layout_macros(
+    orig: &str,
+    indent: Indent,
+    config: &Config,
+) -> Option<String> {
+    let mut lines = LineClasses::new(orig);
+    let (first_line_kind, first_line) = lines.next()?;
+
+    // If a macro delimiter and a string start(`"`) is in the same line, then skip trimming
+    // altogether.
+    if first_line_kind == FullCodeCharKind::StartString {
+        return Some(orig.to_string());
+    }
+
+    let trimmed_lines = trim_left_preserve_layout_lines(lines, indent, config)?;
+    Some(first_line + "\n" + &trimmed_lines)
+}
+
+/// Trim each line based on the minimum indentation of the snippet and
+/// indent line based on `Indent`. First line and lines within a string are skipped
+///
 /// e.g.
 ///
 /// ```rust,compile_fail
-/// foo!{
-/// x,
-/// y,
-/// foo(
-///     a,
-///     b,
-///     c,
-/// ),
-/// }
+/// {
+///         x,
+///         y,
+///         foo(
+///             a,
+///             b,
+///             c,
+///         ),
+///     }


Why was the leading foo! removed?

ytmimi · 2026-09-02T23:23:09Z

-///     c,
-/// ),
-/// }
+/// {
+///         x,
+///         y,
+///         foo(
+///             a,
+///             b,
+///             c,
+///         ),
+///     }
 /// ```
 ///
 /// will become
 ///
 /// ```rust,compile_fail
-/// foo!{
-///     x,
-///     y,
-///     foo(
-///         a,
-///         b,
-///         c,
-///     ),
-/// }
+/// {
+///    x,
+///    y,
+///    foo(
+///        a,
+///        b,
+///        c,
+///    ),
+///}


why was the leading foo! removed?

ytmimi · 2026-09-02T23:26:32Z

+    Some(first_line + "\n" + &trimmed_lines)
+}
+
+pub(crate) fn trim_left_preserve_layout_lines(


Not that it really matters, but I don't think trim_left_preserve_layout_lines needs to be pub(crate) Since it's just an internal helper function for trim_left_preserve_layout and trim_left_preserve_layout_macros.

ytmimi · 2026-09-02T23:27:17Z

 }

-/// Indent each line according to the specified `indent`.
+/// Similar to `[::trim_left_preserve_layout]` but for macros.


It would be good to expand on the docs here and mention why we need an independent function for macros.

rustbot added the S-waiting-on-review Status: awaiting review from the assignee but also interested parties. label Aug 16, 2026

dswij commented Aug 16, 2026

View reviewed changes

Comment thread src/macros.rs

Comment thread src/utils.rs