Remove invalid help diagnostics for const pointer

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -1146,6 +1146,12 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                     }
                     // don't create labels for compiler-generated spans
                     Some(_) => None,
+                    // don't create labels for the span not from user's code
+                    None if opt_assignment_rhs_span
+                        .is_some_and(|span| self.infcx.tcx.sess.source_map().is_imported(span)) =>
+                    {
+                        None
+                    }
                     None => {
                         let (has_sugg, decl_span, sugg) = if name != kw::SelfLower {
                             suggest_ampmut(
@@ -1198,6 +1204,8 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                     sugg.push(s);
                 }
 
+                if sugg.iter().all(|(span, _)| !self.infcx.tcx.sess.source_map().is_imported(*span))
+                {
                     err.multipart_suggestion_verbose(
                         format!(
                             "consider changing this to be a mutable {pointer_desc}{}",
@@ -1211,6 +1219,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                         Applicability::MachineApplicable,
                     );
                 }
+            }
             Some((false, err_label_span, message, _)) => {
                 let def_id = self.body.source.def_id();
                 let hir_id = if let Some(local_def_id) = def_id.as_local()

tests/ui/suggestions/dont_suggest_raw_pointer_syntax-issue-127562.rs

@@ -0,0 +1,7 @@
+fn main() {
+    let val = 2;
+    let ptr = std::ptr::addr_of!(val);
+    unsafe {
+        *ptr = 3; //~ ERROR cannot assign to `*ptr`, which is behind a `*const` pointer
+    }
+}

tests/ui/suggestions/dont_suggest_raw_pointer_syntax-issue-127562.stderr

@@ -0,0 +1,9 @@
+error[E0594]: cannot assign to `*ptr`, which is behind a `*const` pointer
+  --> $DIR/dont_suggest_raw_pointer_syntax-issue-127562.rs:5:9
+   |
+LL |         *ptr = 3;
+   |         ^^^^^^^^ `ptr` is a `*const` pointer, so the data it refers to cannot be written
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0594`.