Implement lint against direct uses of rustc_type_ir in compiler crates

This commit adds a lint to prevent the use of rustc_type_ir in random
compiler crates, except for type system internals traits, which are
explicitly allowed. Moreover, this fixes diagnostic_items() to include
the CRATE_OWNER_ID, otherwise rustc_diagnostic_item attribute is ignored
on the crate root.

2 files changed, 65 insertions, 0 deletions

diff --git a/tests/ui-fulldeps/internal-lints/direct-use-of-rustc-type-ir.rs b/tests/ui-fulldeps/internal-lints/direct-use-of-rustc-type-ir.rs
new file mode 100644
index 00000000000..5c68df4e1e4
--- /dev/null
+++ b/tests/ui-fulldeps/internal-lints/direct-use-of-rustc-type-ir.rs
@@ -0,0 +1,26 @@
+//@ compile-flags: -Z unstable-options
+//@ ignore-stage1
+
+#![feature(rustc_private)]
+#![deny(rustc::direct_use_of_rustc_type_ir)]
+
+extern crate rustc_middle;
+extern crate rustc_type_ir;
+
+use rustc_middle::ty::*; // OK, we have to accept rustc_middle::ty::*
+
+// We have to deny direct import of type_ir
+use rustc_type_ir::*;
+//~^ ERROR: do not use `rustc_type_ir` unless you are implementing type system internals
+
+// We have to deny direct types usages which resolves to type_ir
+fn foo<I: rustc_type_ir::Interner>(cx: I, did: I::DefId) {
+//~^ ERROR: do not use `rustc_type_ir` unless you are implementing type system internals
+}
+
+fn main() {
+    let _ = rustc_type_ir::InferConst::Fresh(42);
+//~^ ERROR: do not use `rustc_type_ir` unless you are implementing type system internals
+    let _: rustc_type_ir::InferConst;
+//~^ ERROR: do not use `rustc_type_ir` unless you are implementing type system internals
+}
diff --git a/tests/ui-fulldeps/internal-lints/direct-use-of-rustc-type-ir.stderr b/tests/ui-fulldeps/internal-lints/direct-use-of-rustc-type-ir.stderr
new file mode 100644
index 00000000000..d1716494d52
--- /dev/null
+++ b/tests/ui-fulldeps/internal-lints/direct-use-of-rustc-type-ir.stderr
@@ -0,0 +1,39 @@
+error: do not use `rustc_type_ir` unless you are implementing type system internals
+  --> $DIR/direct-use-of-rustc-type-ir.rs:13:5
+   |
+LL | use rustc_type_ir::*;
+   |     ^^^^^^^^^^^^^
+   |
+   = note: use `rustc_middle::ty` instead
+note: the lint level is defined here
+  --> $DIR/direct-use-of-rustc-type-ir.rs:5:9
+   |
+LL | #![deny(rustc::direct_use_of_rustc_type_ir)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: do not use `rustc_type_ir` unless you are implementing type system internals
+  --> $DIR/direct-use-of-rustc-type-ir.rs:17:11
+   |
+LL | fn foo<I: rustc_type_ir::Interner>(cx: I, did: I::DefId) {
+   |           ^^^^^^^^^^^^^
+   |
+   = note: use `rustc_middle::ty` instead
+
+error: do not use `rustc_type_ir` unless you are implementing type system internals
+  --> $DIR/direct-use-of-rustc-type-ir.rs:22:13
+   |
+LL |     let _ = rustc_type_ir::InferConst::Fresh(42);
+   |             ^^^^^^^^^^^^^
+   |
+   = note: use `rustc_middle::ty` instead
+
+error: do not use `rustc_type_ir` unless you are implementing type system internals
+  --> $DIR/direct-use-of-rustc-type-ir.rs:24:12
+   |
+LL |     let _: rustc_type_ir::InferConst;
+   |            ^^^^^^^^^^^^^
+   |
+   = note: use `rustc_middle::ty` instead
+
+error: aborting due to 4 previous errors
+