1 files changed, 50 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0446.md b/compiler/rustc_error_codes/src/error_codes/E0446.md
new file mode 100644
index 000000000..6ec47c496
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0446.md
@@ -0,0 +1,50 @@
+A private type was used in a public type signature.
+
+Erroneous code example:
+
+```compile_fail,E0446
+#![deny(private_in_public)]
+struct Bar(u32);
+
+mod foo {
+    use crate::Bar;
+    pub fn bar() -> Bar { // error: private type in public interface
+        Bar(0)
+    }
+}
+
+fn main() {}
+```
+
+There are two ways to solve this error. The first is to make the public type
+signature only public to a module that also has access to the private type.
+This is done by using pub(crate) or pub(in crate::my_mod::etc)
+Example:
+
+```
+struct Bar(u32);
+
+mod foo {
+    use crate::Bar;
+    pub(crate) fn bar() -> Bar { // only public to crate root
+        Bar(0)
+    }
+}
+
+fn main() {}
+```
+
+The other way to solve this error is to make the private type public.
+Example:
+
+```
+pub struct Bar(u32); // we set the Bar type public
+mod foo {
+    use crate::Bar;
+    pub fn bar() -> Bar { // ok!
+        Bar(0)
+    }
+}
+
+fn main() {}
+```