Slides path lifetime to the lifetime resolver

add test to for the fix

add descriptive text for the fix

simplified code logics

update descriptive comments

update to cope with the tidyness requirement

merged commit suggestions

Co-Authored-By: varkor <github@varkor.com>

truncated redundant comments

update to cope with tidy-check

src/librustc/hir/lowering.rs

@@ -3281,10 +3281,14 @@ impl<'a> LoweringContext<'a> {
                 let id = self.sess.next_node_id();
                 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
             }
-            // This is the normal case.
-            AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
-
-            AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
+            // `PassThrough` is the normal case.
+            // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
+            // is unsuitable here, as these can occur from missing lifetime parameters in a
+            // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
+            // lifetime. Instead, we simply create an implicit lifetime, which will be checked
+            // later, at which point a suitable error will be emitted.
+          | AnonymousLifetimeMode::PassThrough
+          | AnonymousLifetimeMode::ReportError => self.new_implicit_lifetime(span),
         }
     }
 

src/test/ui/generics/issue-65285-incorrect-explicit-lifetime-name-needed.rs

@@ -0,0 +1,14 @@
+#![crate_type="lib"]
+
+struct Nested<K>(K);
+
+fn should_error<T>() where T : Into<&u32> {}
+//~^ ERROR `&` without an explicit lifetime name cannot be used here [E0637]
+
+trait X<'a, K: 'a> {
+    fn foo<'b, L: X<&'b Nested<K>>>();
+    //~^ ERROR missing lifetime specifier [E0106]
+}
+
+fn bar<'b, L: X<&'b Nested<i32>>>(){}
+//~^ ERROR missing lifetime specifier [E0106]

src/test/ui/generics/issue-65285-incorrect-explicit-lifetime-name-needed.stderr

@@ -0,0 +1,21 @@
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/issue-65285-incorrect-explicit-lifetime-name-needed.rs:5:37
+   |
+LL | fn should_error<T>() where T : Into<&u32> {}
+   |                                     ^ explicit lifetime name needed here
+
+error[E0106]: missing lifetime specifier
+  --> $DIR/issue-65285-incorrect-explicit-lifetime-name-needed.rs:9:19
+   |
+LL |     fn foo<'b, L: X<&'b Nested<K>>>();
+   |                   ^^^^^^^^^^^^^^^^ expected lifetime parameter
+
+error[E0106]: missing lifetime specifier
+  --> $DIR/issue-65285-incorrect-explicit-lifetime-name-needed.rs:13:15
+   |
+LL | fn bar<'b, L: X<&'b Nested<i32>>>(){}
+   |               ^^^^^^^^^^^^^^^^^^ expected lifetime parameter
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0106`.