From 1aca8fa96cc498916fba912a2500d36a51593db5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Guillermo=20C=C3=A9spedes=20Tab=C3=A1rez?=
 <1295883+dertin@users.noreply.github.com>
Date: Tue, 21 Jul 2026 16:26:13 -0300
Subject: [PATCH 1/2] Use formatting prefix for rustfmt errors

---
 src/bin/main.rs       |  2 +-
 tests/rustfmt/main.rs | 11 +++++++----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/bin/main.rs b/src/bin/main.rs
index 54b267bb445..6eaf709dab3 100644
--- a/src/bin/main.rs
+++ b/src/bin/main.rs
@@ -408,7 +408,7 @@ fn format_and_emit_report<T: Write>(session: &mut Session<'_, T>, input: Input)
             }
         }
         Err(msg) => {
-            eprintln!("Error writing files: {msg}");
+            eprintln!("Error formatting files: {msg}");
             session.add_operational_error();
         }
     }
diff --git a/tests/rustfmt/main.rs b/tests/rustfmt/main.rs
index 4008c8d1435..3e91b040324 100644
--- a/tests/rustfmt/main.rs
+++ b/tests/rustfmt/main.rs
@@ -125,19 +125,22 @@ fn rustfmt_usage_text() {
 }
 
 #[test]
-fn mod_resolution_error_multiple_candidate_files() {
+fn check_mode_mod_resolution_error_uses_formatting_prefix() {
     // See also https://github.com/rust-lang/rustfmt/issues/5167
     let default_path = Path::new("tests/mod-resolver/issue-5167/src/a.rs");
     let secondary_path = Path::new("tests/mod-resolver/issue-5167/src/a/mod.rs");
     let error_message = format!(
-        "file for module found at both {:?} and {:?}",
+        concat!(
+            "Error formatting files: failed to resolve mod `a`: ",
+            "file for module found at both {:?} and {:?}"
+        ),
         default_path.canonicalize().unwrap(),
         secondary_path.canonicalize().unwrap(),
     );
 
-    let args = ["tests/mod-resolver/issue-5167/src/lib.rs"];
+    let args = ["--check", "tests/mod-resolver/issue-5167/src/lib.rs"];
     let (_stdout, stderr) = rustfmt(&args);
-    assert!(stderr.contains(&error_message))
+    assert_eq!(stderr.trim(), error_message)
 }
 
 #[test]

From 3b26500d7ca8fafdc71adbc4a9d9909439e0ff1e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Guillermo=20C=C3=A9spedes=20Tab=C3=A1rez?=
 <1295883+dertin@users.noreply.github.com>
Date: Tue, 21 Jul 2026 16:41:20 -0300
Subject: [PATCH 2/2] Make error prefix test tolerate warnings

---
 tests/rustfmt/main.rs | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tests/rustfmt/main.rs b/tests/rustfmt/main.rs
index 3e91b040324..b1ec556e2d9 100644
--- a/tests/rustfmt/main.rs
+++ b/tests/rustfmt/main.rs
@@ -125,22 +125,26 @@ fn rustfmt_usage_text() {
 }
 
 #[test]
-fn check_mode_mod_resolution_error_uses_formatting_prefix() {
+fn mod_resolution_error_multiple_candidate_files() {
     // See also https://github.com/rust-lang/rustfmt/issues/5167
     let default_path = Path::new("tests/mod-resolver/issue-5167/src/a.rs");
     let secondary_path = Path::new("tests/mod-resolver/issue-5167/src/a/mod.rs");
     let error_message = format!(
-        concat!(
-            "Error formatting files: failed to resolve mod `a`: ",
-            "file for module found at both {:?} and {:?}"
-        ),
+        "file for module found at both {:?} and {:?}",
         default_path.canonicalize().unwrap(),
         secondary_path.canonicalize().unwrap(),
     );
 
+    let args = ["tests/mod-resolver/issue-5167/src/lib.rs"];
+    let (_stdout, stderr) = rustfmt(&args);
+    assert!(stderr.contains(&error_message))
+}
+
+#[test]
+fn check_mode_error_uses_formatting_prefix() {
     let args = ["--check", "tests/mod-resolver/issue-5167/src/lib.rs"];
     let (_stdout, stderr) = rustfmt(&args);
-    assert_eq!(stderr.trim(), error_message)
+    assert!(stderr.contains("Error formatting files:"))
 }
 
 #[test]