docs/test: add UI test and long-form error docs for E0519

src/test/ui/error-codes/E0519.rs

@@ -0,0 +1,8 @@
+// no need to create a new aux file, we can use an existing.
+// aux-build: crateresolve1-1.rs
+
+// set same metadata as `crateresolve1`
+#![crate_name = "crateresolve1"]
+#![crate_type = "lib"]
+
+extern crate crateresolve1; //~ ERROR E0519

src/test/ui/error-codes/E0519.stderr

@@ -0,0 +1,9 @@
+error[E0519]: the current crate is indistinguishable from one of its dependencies: it has the same crate-name `crateresolve1` and was compiled with the same `-C metadata` arguments. This will result in symbol conflicts between the two.
+  --> $DIR/E0519.rs:8:1
+   |
+LL | extern crate crateresolve1;
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0519`.

src/tools/tidy/src/error_codes_check.rs

@@ -11,8 +11,8 @@ use regex::Regex;
 
 // A few of those error codes can't be tested but all the others can and *should* be tested!
 const EXEMPTED_FROM_TEST: &[&str] = &[
-    "E0313", "E0461", "E0465", "E0476", "E0490", "E0514", "E0519", "E0523", "E0554", "E0640",
-    "E0717", "E0729", "E0789",
+    "E0313", "E0461", "E0465", "E0476", "E0490", "E0514", "E0523", "E0554", "E0640", "E0717",
+    "E0729", "E0789",
 ];
 
 // Some error codes don't have any tests apparently...