From c5e0d6e4d43f228687c75ab7406f64b318752d7b Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Sun, 6 Oct 2019 15:23:33 +0200
Subject: [PATCH 1/2] Add long error explanation for E0566

---
 src/librustc/error_codes.rs | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/librustc/error_codes.rs b/src/librustc/error_codes.rs
index 66c51000066..9a5e1ea6f33 100644
--- a/src/librustc/error_codes.rs
+++ b/src/librustc/error_codes.rs
@@ -1700,6 +1700,30 @@ To understand better how closures work in Rust, read:
 https://doc.rust-lang.org/book/ch13-01-closures.html
 "##,
 
+E0566: r##"
+Conflicting representation hints have been used on a same item.
+
+Erroneous code example:
+
+```compile_fail,E0566
+# #![deny(warnings)]
+# fn main() {
+#[repr(u32, u64)] // error!
+enum Repr { A }
+# }
+```
+
+In most cases (if not all), using just one representation hint is more than
+enough. If you want to have a representation hint depending on the current
+architecture, use `cfg_attr`. Example:
+
+```
+#[cfg_attr(linux, repr(u32))]
+#[cfg_attr(not(linux), repr(u64))]
+enum Repr { A }
+```
+"##,
+
 E0580: r##"
 The `main` function was incorrectly declared.
 
@@ -2097,7 +2121,6 @@ rejected in your own crates.
     E0490, // a value of type `..` is borrowed for too long
     E0495, // cannot infer an appropriate lifetime due to conflicting
            // requirements
-    E0566, // conflicting representation hints
     E0623, // lifetime mismatch where both parameters are anonymous regions
     E0628, // generators cannot have explicit parameters
     E0631, // type mismatch in closure arguments

From 57cb8819ee78f2debf24d2e123c78796204db8c9 Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Sun, 6 Oct 2019 17:02:01 +0200
Subject: [PATCH 2/2] Update ui tests

---
 src/librustc/error_codes.rs                             | 7 ++-----
 src/test/ui/conflicting-repr-hints.stderr               | 1 +
 src/test/ui/feature-gates/feature-gate-repr-simd.stderr | 3 ++-
 3 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/librustc/error_codes.rs b/src/librustc/error_codes.rs
index 9a5e1ea6f33..502172db91c 100644
--- a/src/librustc/error_codes.rs
+++ b/src/librustc/error_codes.rs
@@ -1705,12 +1705,9 @@ Conflicting representation hints have been used on a same item.
 
 Erroneous code example:
 
-```compile_fail,E0566
-# #![deny(warnings)]
-# fn main() {
-#[repr(u32, u64)] // error!
+```
+#[repr(u32, u64)] // warning!
 enum Repr { A }
-# }
 ```
 
 In most cases (if not all), using just one representation hint is more than
diff --git a/src/test/ui/conflicting-repr-hints.stderr b/src/test/ui/conflicting-repr-hints.stderr
index 6b15b7ebbe9..832f5c3ac2b 100644
--- a/src/test/ui/conflicting-repr-hints.stderr
+++ b/src/test/ui/conflicting-repr-hints.stderr
@@ -66,3 +66,4 @@ LL | | }
 
 error: aborting due to 8 previous errors
 
+For more information about this error, try `rustc --explain E0566`.
diff --git a/src/test/ui/feature-gates/feature-gate-repr-simd.stderr b/src/test/ui/feature-gates/feature-gate-repr-simd.stderr
index dfaa85bc5f0..02c8400e03e 100644
--- a/src/test/ui/feature-gates/feature-gate-repr-simd.stderr
+++ b/src/test/ui/feature-gates/feature-gate-repr-simd.stderr
@@ -26,4 +26,5 @@ LL | #[repr(simd)]
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0658`.
+Some errors have detailed explanations: E0566, E0658.
+For more information about an error, try `rustc --explain E0566`.