fix: Alloc new errorcode E0803 for E0495

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

compiler/rustc_error_codes/src/error_codes/E0803.md

@@ -0,0 +1,46 @@
+A trait implementation returns a reference without an
+explicit lifetime linking it to `self`.
+It commonly arises in generic trait implementations
+requiring explicit lifetime bounds.
+
+Erroneous code example:
+
+```compile_fail,E0803
+trait DataAccess<T> {
+    fn get_ref(&self) -> T;
+}
+
+struct Container<'a> {
+    value: &'a f64,
+}
+
+// Attempting to implement reference return
+impl<'a> DataAccess<&f64> for Container<'a> {
+    fn get_ref(&self) -> &f64 { // Error: Lifetime mismatch
+        self.value
+    }
+}
+```
+
+The trait method returns &f64 requiring an independent lifetime
+The struct Container<'a> carries lifetime parameter 'a
+The compiler cannot verify if the returned reference satisfies 'a constraints
+Solution
+Explicitly bind lifetimes to clarify constraints:
+```
+// Modified trait with explicit lifetime binding
+trait DataAccess<'a, T> {
+    fn get_ref(&'a self) -> T;
+}
+
+struct Container<'a> {
+    value: &'a f64,
+}
+
+// Correct implementation (bound lifetimes)
+impl<'a> DataAccess<'a, &'a f64> for Container<'a> {
+    fn get_ref(&'a self) -> &'a f64 {
+        self.value
+    }
+}
+```

compiler/rustc_error_codes/src/lib.rs

@@ -546,6 +546,7 @@ E0799: 0799,
 E0800: 0800,
 E0801: 0801,
 E0802: 0802,
+E0803: 0803,
         );
     )
 }

compiler/rustc_trait_selection/src/error_reporting/infer/region.rs

@@ -2,7 +2,7 @@ use std::iter;
 
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::{
-    Applicability, Diag, E0309, E0310, E0311, E0495, Subdiagnostic, struct_span_code_err,
+    Applicability, Diag, E0309, E0310, E0311, E0803, Subdiagnostic, struct_span_code_err,
 };
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -1032,7 +1032,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         struct_span_code_err!(
             self.dcx(),
             var_origin.span(),
-            E0495,
+            E0803,
             "cannot infer an appropriate lifetime{} due to conflicting requirements",
             var_description
         )