Only give autofix suggestion when no named args are present

compiler/rustc_builtin_macros/src/errors.rs

@@ -646,7 +646,7 @@ pub(crate) struct FormatRedundantArgs {
     pub(crate) note: MultiSpan,
 
     #[subdiagnostic]
-    pub(crate) sugg: FormatRedundantArgsSugg,
+    pub(crate) sugg: Option<FormatRedundantArgsSugg>,
 }
 
 #[derive(Subdiagnostic)]

compiler/rustc_builtin_macros/src/format.rs

@@ -758,11 +758,17 @@ fn report_redundant_format_arguments<'a>(
             suggestion_spans.push(span);
         }
 
+        let sugg = if args.named_args().len() == 0 {
+            Some(errors::FormatRedundantArgsSugg { spans: suggestion_spans })
+        } else {
+            None
+        };
+
         return Some(ecx.create_err(errors::FormatRedundantArgs {
             n: args_spans.len(),
             span: MultiSpan::from(args_spans),
             note: multispan,
-            sugg: errors::FormatRedundantArgsSugg { spans: suggestion_spans },
+            sugg,
         }));
     }
 

tests/ui/did_you_mean/issue-105225-named-args.rs

@@ -0,0 +1,10 @@
+fn main() {
+    let x = "x";
+    let y = "y";
+
+    println!("{x}", x, x = y);
+    //~^ ERROR: redundant argument
+
+    println!("{x}", x = y, x = y);
+    //~^ ERROR: duplicate argument named `x`
+}

tests/ui/did_you_mean/issue-105225-named-args.stderr

@@ -0,0 +1,22 @@
+error: redundant argument
+  --> $DIR/issue-105225-named-args.rs:5:21
+   |
+LL |     println!("{x}", x, x = y);
+   |                     ^
+   |
+note: the formatting specifier is referencing the binding already
+  --> $DIR/issue-105225-named-args.rs:5:16
+   |
+LL |     println!("{x}", x, x = y);
+   |                ^
+
+error: duplicate argument named `x`
+  --> $DIR/issue-105225-named-args.rs:8:28
+   |
+LL |     println!("{x}", x = y, x = y);
+   |                     -      ^ duplicate argument
+   |                     |
+   |                     previously here
+
+error: aborting due to 2 previous errors
+

tests/ui/did_you_mean/issue-105225.fixed

@@ -1,8 +1,8 @@
 // run-rustfix
 
 fn main() {
-    let x = 0;
-    let y = 0;
+    let x = "x";
+    let y = "y";
 
     println!("{x}", );
     //~^ ERROR: redundant argument

tests/ui/did_you_mean/issue-105225.rs

@@ -1,8 +1,8 @@
 // run-rustfix
 
 fn main() {
-    let x = 0;
-    let y = 0;
+    let x = "x";
+    let y = "y";
 
     println!("{x}", x);
     //~^ ERROR: redundant argument