rustc_resolve: Test the order that preludes are resolved

Author: jyn514

Diff for: tests/ui/resolve/auxiliary/tracing.rs

@@ -0,0 +1,11 @@
+#![feature(decl_macro)]
+
+pub use std::clone::Clone as instrument; // macro_use/extern/tool
+pub use std::clone::Clone as global_allocator;   // library
+pub use std::clone::Clone as deprecated;      // lang
+
+mod inner {
+    pub macro some_macro {
+        () => {}
+    }
+}

Diff for: tests/ui/resolve/prelude-order.rs

@@ -0,0 +1,69 @@
+//@ aux-build:tracing.rs
+//@ compile-flags: --crate-type=lib
+
+#![feature(register_tool)]
+
+/* tool prelude */
+#![register_tool(instrument)]  // macro_use/extern prelude
+#![register_tool(must_use)]  // lang prelude
+#![register_tool(test)] // library prelude
+
+/* extern prelude */
+extern crate tracing as usize; // lang prelude
+extern crate tracing as Option; // libs prelude
+extern crate tracing as instrument; // macro_use/tool prelude
+
+/* macro_use prelude */
+#[macro_use]
+extern crate tracing; // also extern prelude
+
+/* lang and libs implicitly in scope */
+
+// tool/extern -> extern
+// NOTE: macro_use/libs/lang not tested (not present)
+#[tracing::inner::some_macro] //~ ERROR `inner` is private
+fn foo() {}
+
+// tool/lang -> tool (no possible conflict)
+// NOTE: macro_use/libs/extern not tested (not present)
+#[must_use::inner] // ok
+fn f() {}
+
+// tool/libs -> tool
+// NOTE: extern/lang/macro not tested (not present)
+#[test::not_real] // ok
+fn b() {}
+
+// tool/extern/macro_use -> extern
+// NOTE: lang/libs not tested (not present)
+#[instrument::inner] //~ ERROR could not find `inner`
+fn a() {}
+
+// extern/lang -> lang
+// NOTE: macro_use/libs/tool not tested (different namespace/not present/wrong context)
+fn bar() -> usize { // ok
+    0
+}
+
+// extern/libs -> extern
+// NOTE: macro_use/lang/tool not tested (not present)
+fn baz() -> Option<i32> { //~ ERROR: expected type, found crate
+    0
+}
+
+// macro/lang -> ambiguous
+// NOTE: tool/libs/extern not tested (not present)
+#[deprecated] //~ ERROR ambiguous
+fn e() {}
+
+// macro/libs -> macro
+// NOTE: tool/lang/extern not tested (not present)
+#[global_allocator] //~ ERROR derive macro
+fn d() {}
+
+// lang/libs -> lang
+// NOTE: tool/extern/macro not tested (not present)
+// FIXME: this is not actually a good test. `cfg!` is a bang-style macro and so ignored here.
+// On the other hand, we control both lang and libs so it doesn't really matter.
+#[cfg(FALSE)] // ok
+fn g() {}

Diff for: tests/ui/resolve/prelude-order.stderr

@@ -0,0 +1,55 @@
+error: expected attribute, found derive macro `global_allocator`
+  --> $DIR/prelude-order.rs:61:3
+   |
+LL | #[global_allocator]
+   |   ^^^^^^^^^^^^^^^^ not an attribute
+
+error[E0433]: failed to resolve: could not find `inner` in `instrument`
+  --> $DIR/prelude-order.rs:39:15
+   |
+LL | #[instrument::inner]
+   |               ^^^^^ could not find `inner` in `instrument`
+
+error[E0573]: expected type, found crate `Option`
+  --> $DIR/prelude-order.rs:50:13
+   |
+LL | fn baz() -> Option<i32> {
+   |             ^^^^^^^^^^^ not a type
+   |
+help: consider importing this enum instead
+   |
+LL + use std::option::Option;
+   |
+
+error[E0659]: `deprecated` is ambiguous
+  --> $DIR/prelude-order.rs:56:3
+   |
+LL | #[deprecated]
+   |   ^^^^^^^^^^ ambiguous name
+   |
+   = note: ambiguous because of a name conflict with a builtin attribute
+   = note: `deprecated` could refer to a built-in attribute
+note: `deprecated` could also refer to the derive macro imported here
+  --> $DIR/prelude-order.rs:17:1
+   |
+LL | #[macro_use]
+   | ^^^^^^^^^^^^
+
+error[E0603]: module `inner` is private
+  --> $DIR/prelude-order.rs:24:12
+   |
+LL | #[tracing::inner::some_macro]
+   |            ^^^^^  ---------- macro `some_macro` is not publicly re-exported
+   |            |
+   |            private module
+   |
+note: the module `inner` is defined here
+  --> $DIR/auxiliary/tracing.rs:7:1
+   |
+LL | mod inner {
+   | ^^^^^^^^^
+
+error: aborting due to 5 previous errors
+
+Some errors have detailed explanations: E0433, E0573, E0603, E0659.
+For more information about an error, try `rustc --explain E0433`.