Rollup merge of #137059 - xizheyin:issue-136827, r=davidtwco

fix: Alloc new errorcode E0803 for E0495

As discussion in #136827, I alloc a new errorcode.

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
         )

tests/ui/implied-bounds/impl-implied-bounds-compatibility-unnormalized.stderr

@@ -1,4 +1,4 @@
-error[E0495]: cannot infer an appropriate lifetime for lifetime parameter 's in generic type due to conflicting requirements
+error[E0803]: cannot infer an appropriate lifetime for lifetime parameter 's in generic type due to conflicting requirements
   --> $DIR/impl-implied-bounds-compatibility-unnormalized.rs:11:5
    |
 LL |     fn get<'s>(s: &'s str, _: <&'static &'s () as Project>::Ty) -> &'static str {
@@ -25,4 +25,4 @@ LL |     fn get<'s>(s: &'s str, _: <&'static &'s () as Project>::Ty) -> &'static
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0495`.
+For more information about this error, try `rustc --explain E0803`.

tests/ui/issues/issue-20831-debruijn.stderr

@@ -1,4 +1,4 @@
-error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
+error[E0803]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
   --> $DIR/issue-20831-debruijn.rs:28:33
    |
 LL |     fn subscribe(&mut self, t : Box<dyn Subscriber<Input=<Self as Publisher>::Output> + 'a>) {
@@ -48,4 +48,4 @@ LL |     fn subscribe(&mut self, t : Box<dyn Subscriber<Input=<Self as Publisher
 
 error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0495`.
+For more information about this error, try `rustc --explain E0803`.

tests/ui/nll/normalization-bounds-error.stderr

@@ -1,4 +1,4 @@
-error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'d` due to conflicting requirements
+error[E0803]: cannot infer an appropriate lifetime for lifetime parameter `'d` due to conflicting requirements
   --> $DIR/normalization-bounds-error.rs:12:31
    |
 LL | fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
@@ -36,4 +36,4 @@ LL | fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0495`.
+For more information about this error, try `rustc --explain E0803`.

tests/ui/regions/regions-normalize-in-where-clause-list.stderr

@@ -1,4 +1,4 @@
-error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
+error[E0803]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
   --> $DIR/regions-normalize-in-where-clause-list.rs:24:4
    |
 LL | fn bar<'a, 'b>()
@@ -24,4 +24,4 @@ LL | fn bar<'a, 'b>()
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0495`.
+For more information about this error, try `rustc --explain E0803`.

tests/ui/regions/resolve-re-error-ice.stderr

@@ -1,4 +1,4 @@
-error[E0495]: cannot infer an appropriate lifetime for lifetime parameter '_ in generic type due to conflicting requirements
+error[E0803]: cannot infer an appropriate lifetime for lifetime parameter '_ in generic type due to conflicting requirements
   --> $DIR/resolve-re-error-ice.rs:12:5
    |
 LL |     fn key_set(&self) -> Subject<'a, Keys<K, V>, (), R> {
@@ -34,4 +34,4 @@ LL | struct Subject<'a, T, V, R>(PhantomData<(&'a T, V, R)>);
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0495`.
+For more information about this error, try `rustc --explain E0803`.

tests/ui/static/static-lifetime.stderr

@@ -11,7 +11,7 @@ LL | impl<'a, A: Clone> Arbitrary for ::std::borrow::Cow<'a, A> {}
    |      ^^
    = note: but lifetime parameter must outlive the static lifetime
 
-error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
+error[E0803]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
   --> $DIR/static-lifetime.rs:3:34
    |
 LL | impl<'a, A: Clone> Arbitrary for ::std::borrow::Cow<'a, A> {}
@@ -38,5 +38,5 @@ LL | impl<'a, A: Clone> Arbitrary for ::std::borrow::Cow<'a, A> {}
 
 error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0478, E0495.
+Some errors have detailed explanations: E0478, E0803.
 For more information about an error, try `rustc --explain E0478`.

tests/ui/traits/impl-of-supertrait-has-wrong-lifetime-parameters.stderr

@@ -1,4 +1,4 @@
-error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'b` due to conflicting requirements
+error[E0803]: cannot infer an appropriate lifetime for lifetime parameter `'b` due to conflicting requirements
   --> $DIR/impl-of-supertrait-has-wrong-lifetime-parameters.rs:24:28
    |
 LL | impl<'a,'b> T2<'a, 'b> for S<'a, 'b> {
@@ -24,4 +24,4 @@ LL | impl<'a,'b> T2<'a, 'b> for S<'a, 'b> {
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0495`.
+For more information about this error, try `rustc --explain E0803`.

tests/ui/type-alias-impl-trait/closure_wf_outlives.stderr

@@ -15,7 +15,7 @@ note: but lifetime parameter must outlive the lifetime `'b` as defined here
 LL |     type Opaque<'a, 'b> = impl Sized + 'a + 'b;
    |                     ^^
 
-error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
+error[E0803]: cannot infer an appropriate lifetime due to conflicting requirements
   --> $DIR/closure_wf_outlives.rs:34:9
    |
 LL |         || {}
@@ -63,5 +63,5 @@ LL |     type Opaque<T: 'static> = impl Sized;
 
 error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0310, E0478, E0495.
+Some errors have detailed explanations: E0310, E0478, E0803.
 For more information about an error, try `rustc --explain E0310`.