From 475e4eeb6557af820ee2b48f213f178eca5e11ce Mon Sep 17 00:00:00 2001
From: Jeremy Banks <_@jeremy.ca>
Date: Mon, 7 Feb 2022 23:40:17 +0000
Subject: [PATCH] Remove obsolete no-op #[main] attribute from compiler.

---
 compiler/rustc_feature/src/builtin_attrs.rs          |  1 -
 src/test/ui/attributes/main-removed-1.rs             |  2 ++
 src/test/ui/attributes/main-removed-1.stderr         | 10 ++++++++++
 .../ui/attributes/main-removed-2/auxiliary/tokyo.rs  | 12 ++++++++++++
 src/test/ui/attributes/main-removed-2/main.rs        | 11 +++++++++++
 5 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/attributes/main-removed-1.rs
 create mode 100644 src/test/ui/attributes/main-removed-1.stderr
 create mode 100644 src/test/ui/attributes/main-removed-2/auxiliary/tokyo.rs
 create mode 100644 src/test/ui/attributes/main-removed-2/main.rs

diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index cb2562d09a525..b224c64ece7f6 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -339,7 +339,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
 
     // Entry point:
-    ungated!(main, Normal, template!(Word), WarnFollowing),
     ungated!(start, Normal, template!(Word), WarnFollowing),
     ungated!(no_start, CrateLevel, template!(Word), WarnFollowing),
     ungated!(no_main, CrateLevel, template!(Word), WarnFollowing),
diff --git a/src/test/ui/attributes/main-removed-1.rs b/src/test/ui/attributes/main-removed-1.rs
new file mode 100644
index 0000000000000..0e887469d4466
--- /dev/null
+++ b/src/test/ui/attributes/main-removed-1.rs
@@ -0,0 +1,2 @@
+#[main]  //~ ERROR cannot find attribute `main` in this scope
+fn main() {}
diff --git a/src/test/ui/attributes/main-removed-1.stderr b/src/test/ui/attributes/main-removed-1.stderr
new file mode 100644
index 0000000000000..2422c5c3b6239
--- /dev/null
+++ b/src/test/ui/attributes/main-removed-1.stderr
@@ -0,0 +1,10 @@
+error: cannot find attribute `main` in this scope
+  --> $DIR/main-removed-1.rs:1:3
+   |
+LL | #[main]
+   |   ^^^^
+   |
+   = note: `main` is in scope, but it is a function, not an attribute
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/attributes/main-removed-2/auxiliary/tokyo.rs b/src/test/ui/attributes/main-removed-2/auxiliary/tokyo.rs
new file mode 100644
index 0000000000000..196b5be2dd086
--- /dev/null
+++ b/src/test/ui/attributes/main-removed-2/auxiliary/tokyo.rs
@@ -0,0 +1,12 @@
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro_attribute]
+pub fn main(_: TokenStream, input: TokenStream) -> TokenStream {
+    "fn main() { println!(\"Hello Tokyo!\"); }".parse().unwrap()
+}
diff --git a/src/test/ui/attributes/main-removed-2/main.rs b/src/test/ui/attributes/main-removed-2/main.rs
new file mode 100644
index 0000000000000..e8fecf825fa83
--- /dev/null
+++ b/src/test/ui/attributes/main-removed-2/main.rs
@@ -0,0 +1,11 @@
+// run-pass
+// aux-build:tokyo.rs
+// compile-flags:--extern tokyo
+// edition:2021
+
+use tokyo::main;
+
+#[main]
+fn main() {
+    panic!("the #[main] macro should replace this with non-panicking code")
+}