From 5bbc240ffbb0dcf510fd73d71dae529bd345e6b2 Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Sat, 15 May 2021 16:10:17 -0700
Subject: [PATCH] Fix unused attributes on macro_rules.

---
 compiler/rustc_lint/src/late.rs               |  4 +++
 compiler/rustc_target/src/asm/mod.rs          |  3 --
 src/test/ui/unused/unused-attr-macro-rules.rs | 34 +++++++++++++++++++
 .../ui/unused/unused-attr-macro-rules.stderr  | 32 +++++++++++++++++
 4 files changed, 70 insertions(+), 3 deletions(-)
 create mode 100644 src/test/ui/unused/unused-attr-macro-rules.rs
 create mode 100644 src/test/ui/unused/unused-attr-macro-rules.stderr

diff --git a/compiler/rustc_lint/src/late.rs b/compiler/rustc_lint/src/late.rs
index d325b5fe7f8c6..0a7ab4a2bafa3 100644
--- a/compiler/rustc_lint/src/late.rs
+++ b/compiler/rustc_lint/src/late.rs
@@ -448,6 +448,10 @@ fn late_lint_pass_crate<'tcx, T: LateLintPass<'tcx>>(tcx: TyCtxt<'tcx>, pass: T)
         lint_callback!(cx, check_crate, krate);
 
         hir_visit::walk_crate(cx, krate);
+        for attr in krate.non_exported_macro_attrs {
+            // This HIR ID is a lie, since the macro ID isn't available.
+            cx.visit_attribute(hir::CRATE_HIR_ID, attr);
+        }
 
         lint_callback!(cx, check_crate_post, krate);
     })
diff --git a/compiler/rustc_target/src/asm/mod.rs b/compiler/rustc_target/src/asm/mod.rs
index f12debb5a3412..f4e4579bec27e 100644
--- a/compiler/rustc_target/src/asm/mod.rs
+++ b/compiler/rustc_target/src/asm/mod.rs
@@ -6,7 +6,6 @@ use rustc_span::Symbol;
 use std::fmt;
 use std::str::FromStr;
 
-#[macro_use]
 macro_rules! def_reg_class {
     ($arch:ident $arch_regclass:ident {
         $(
@@ -51,7 +50,6 @@ macro_rules! def_reg_class {
     }
 }
 
-#[macro_use]
 macro_rules! def_regs {
     ($arch:ident $arch_reg:ident $arch_regclass:ident {
         $(
@@ -129,7 +127,6 @@ macro_rules! def_regs {
     }
 }
 
-#[macro_use]
 macro_rules! types {
     (
         $(_ : $($ty:expr),+;)?
diff --git a/src/test/ui/unused/unused-attr-macro-rules.rs b/src/test/ui/unused/unused-attr-macro-rules.rs
new file mode 100644
index 0000000000000..396137a11d069
--- /dev/null
+++ b/src/test/ui/unused/unused-attr-macro-rules.rs
@@ -0,0 +1,34 @@
+#![deny(unused_attributes)]
+// Unused attributes on macro_rules requires special handling since the
+// macro_rules definition does not survive towards HIR.
+
+// A sample of various built-in attributes.
+#[macro_export]
+#[macro_use] //~ ERROR unused attribute
+#[path="foo"] //~ ERROR unused attribute
+#[recursion_limit="1"] //~ ERROR unused attribute
+                       //~| ERROR crate-level attribute should be an inner attribute
+macro_rules! foo {
+    () => {};
+}
+
+// The following should not warn about unused attributes.
+#[allow(unused)]
+macro_rules! foo2 {
+    () => {};
+}
+
+#[cfg(FALSE)]
+macro_rules! foo {
+    () => {};
+}
+
+/// Some docs
+#[deprecated]
+#[doc = "more docs"]
+#[macro_export]
+macro_rules! bar {
+    () => {};
+}
+
+fn main() {}
diff --git a/src/test/ui/unused/unused-attr-macro-rules.stderr b/src/test/ui/unused/unused-attr-macro-rules.stderr
new file mode 100644
index 0000000000000..4606be01ac014
--- /dev/null
+++ b/src/test/ui/unused/unused-attr-macro-rules.stderr
@@ -0,0 +1,32 @@
+error: unused attribute
+  --> $DIR/unused-attr-macro-rules.rs:7:1
+   |
+LL | #[macro_use]
+   | ^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-attr-macro-rules.rs:1:9
+   |
+LL | #![deny(unused_attributes)]
+   |         ^^^^^^^^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-macro-rules.rs:8:1
+   |
+LL | #[path="foo"]
+   | ^^^^^^^^^^^^^
+
+error: unused attribute
+  --> $DIR/unused-attr-macro-rules.rs:9:1
+   |
+LL | #[recursion_limit="1"]
+   | ^^^^^^^^^^^^^^^^^^^^^^
+
+error: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
+  --> $DIR/unused-attr-macro-rules.rs:9:1
+   |
+LL | #[recursion_limit="1"]
+   | ^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors
+