docs(error-codes): Add long error explanation for E0227

2 files changed, 34 insertions, 1 deletions

diff --git a/compiler/rustc_error_codes/src/error_codes.rs b/compiler/rustc_error_codes/src/error_codes.rs
index ce26ff62235..79d9c55b547 100644
--- a/compiler/rustc_error_codes/src/error_codes.rs
+++ b/compiler/rustc_error_codes/src/error_codes.rs
@@ -120,6 +120,7 @@ E0223: include_str!("./error_codes/E0223.md"),
 E0224: include_str!("./error_codes/E0224.md"),
 E0225: include_str!("./error_codes/E0225.md"),
 E0226: include_str!("./error_codes/E0226.md"),
+E0227: include_str!("./error_codes/E0227.md"),
 E0228: include_str!("./error_codes/E0228.md"),
 E0229: include_str!("./error_codes/E0229.md"),
 E0230: include_str!("./error_codes/E0230.md"),
@@ -530,7 +531,6 @@ E0786: include_str!("./error_codes/E0786.md"),
 //  E0217, // ambiguous associated type, defined in multiple supertraits
 //  E0218, // no associated type defined
 //  E0219, // associated type defined in higher-ranked supertrait
-    E0227, // ambiguous lifetime bound, explicit lifetime bound required
 //  E0233,
 //  E0234,
 //  E0235, // structure constructor specifies a structure of type but
diff --git a/compiler/rustc_error_codes/src/error_codes/E0227.md b/compiler/rustc_error_codes/src/error_codes/E0227.md
new file mode 100644
index 00000000000..f68614723d4
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0227.md
@@ -0,0 +1,33 @@
+This error indicates that the compiler is unable to determine whether there is
+exactly one unique region in the set of derived region bounds.
+
+Example of erroneous code:
+
+```compile_fail,E0227
+trait Foo<'foo>: 'foo {}
+trait Bar<'bar>: 'bar {}
+
+trait FooBar<'foo, 'bar>: Foo<'foo> + Bar<'bar> {}
+
+struct Baz<'foo, 'bar> {
+    baz: dyn FooBar<'foo, 'bar>,
+}
+```
+
+Here, `baz` can have either `'foo` or `'bar` lifetimes.
+
+To resolve this error, provide an explicit lifetime:
+
+```rust
+trait Foo<'foo>: 'foo {}
+trait Bar<'bar>: 'bar {}
+
+trait FooBar<'foo, 'bar>: Foo<'foo> + Bar<'bar> {}
+
+struct Baz<'foo, 'bar, 'baz>
+where
+    'baz: 'foo + 'bar,
+{
+    obj: dyn FooBar<'foo, 'bar> + 'baz,
+}
+```