From 6e36eb22ffb7b5aaeac7d009b7e3c5b4d1297577 Mon Sep 17 00:00:00 2001
From: subotac <73706465+subotac@users.noreply.github.com>
Date: Mon, 3 Aug 2026 00:34:48 +0300
Subject: [PATCH 1/2] Fix chain formatting with pre-existing overflow

---
 src/chains.rs                                 | 14 +++++++++++++-
 tests/source/issue_6977_style_edition_2024.rs | 11 +++++++++++
 tests/source/issue_6977_style_edition_2027.rs | 11 +++++++++++
 tests/target/issue_6977_style_edition_2024.rs | 11 +++++++++++
 tests/target/issue_6977_style_edition_2027.rs | 12 ++++++++++++
 5 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 tests/source/issue_6977_style_edition_2024.rs
 create mode 100644 tests/source/issue_6977_style_edition_2027.rs
 create mode 100644 tests/target/issue_6977_style_edition_2024.rs
 create mode 100644 tests/target/issue_6977_style_edition_2027.rs

diff --git a/src/chains.rs b/src/chains.rs
index 90adb67ad43..0f281170d82 100644
--- a/src/chains.rs
+++ b/src/chains.rs
@@ -582,7 +582,19 @@ impl Rewrite for Chain {
         formatter.format_last_child(context, shape, child_shape)?;
 
         let result = formatter.join_rewrites(context, child_shape)?;
-        wrap_str(result, context.config.max_width(), shape).max_width_error(shape.width, full_span)
+        let max_width = if context.config.style_edition() >= StyleEdition::Edition2027 {
+            // Keep formatting the chain when a nested expression contains an unavoidable,
+            // pre-existing overflow, but do not allow the rewrite to make it any wider.
+            crate::comment::filter_normal_code(context.snippet(full_span))
+                .lines()
+                .map(utils::unicode_str_width)
+                .max()
+                .unwrap_or(0)
+                .max(context.config.max_width())
+        } else {
+            context.config.max_width()
+        };
+        wrap_str(result, max_width, shape).max_width_error(shape.width, full_span)
     }
 }
 
diff --git a/tests/source/issue_6977_style_edition_2024.rs b/tests/source/issue_6977_style_edition_2024.rs
new file mode 100644
index 00000000000..9d9ce30a5c3
--- /dev/null
+++ b/tests/source/issue_6977_style_edition_2024.rs
@@ -0,0 +1,11 @@
+// rustfmt-style_edition: 2024
+
+fn main() {
+    some_struct.foo(format!(
+        "{}", if true {
+            "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+                    } else {
+            ""
+        },
+    ));
+}
diff --git a/tests/source/issue_6977_style_edition_2027.rs b/tests/source/issue_6977_style_edition_2027.rs
new file mode 100644
index 00000000000..fe5bdc9a0fd
--- /dev/null
+++ b/tests/source/issue_6977_style_edition_2027.rs
@@ -0,0 +1,11 @@
+// rustfmt-style_edition: 2027
+
+fn main() {
+    some_struct.foo(format!(
+        "{}", if true {
+            "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+                    } else {
+            ""
+        },
+    ));
+}
diff --git a/tests/target/issue_6977_style_edition_2024.rs b/tests/target/issue_6977_style_edition_2024.rs
new file mode 100644
index 00000000000..9d9ce30a5c3
--- /dev/null
+++ b/tests/target/issue_6977_style_edition_2024.rs
@@ -0,0 +1,11 @@
+// rustfmt-style_edition: 2024
+
+fn main() {
+    some_struct.foo(format!(
+        "{}", if true {
+            "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+                    } else {
+            ""
+        },
+    ));
+}
diff --git a/tests/target/issue_6977_style_edition_2027.rs b/tests/target/issue_6977_style_edition_2027.rs
new file mode 100644
index 00000000000..8af0f1392f0
--- /dev/null
+++ b/tests/target/issue_6977_style_edition_2027.rs
@@ -0,0 +1,12 @@
+// rustfmt-style_edition: 2027
+
+fn main() {
+    some_struct.foo(format!(
+        "{}",
+        if true {
+            "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+        } else {
+            ""
+        },
+    ));
+}

From 5f804ff584a887233ace15e3530ce26d2d1f2203 Mon Sep 17 00:00:00 2001
From: subotac <73706465+subotac@users.noreply.github.com>
Date: Wed, 30 Sep 2026 23:10:03 +0300
Subject: [PATCH 2/2] Format chain width check

---
 src/chains.rs | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/src/chains.rs b/src/chains.rs
index cb3a63ed8e5..d3beb8907b9 100644
--- a/src/chains.rs
+++ b/src/chains.rs
@@ -603,13 +603,8 @@ impl Rewrite for Chain {
         } else {
             context.config.max_width()
         };
-        wrap_str(
-            result,
-            max_width,
-            context.config.tab_spaces(),
-            shape,
-        )
-        .max_width_error(shape.width, full_span)
+        wrap_str(result, max_width, context.config.tab_spaces(), shape)
+            .max_width_error(shape.width, full_span)
     }
 }