Auto merge of #50030 - flip1995:rfc2103, r=petrochenkov

Implement tool_attributes feature (RFC 2103)

cc #44690

This is currently just a rebased and compiling (hopefully) version of #47773.

Let's see if travis likes this. I will add the implementation for `tool_lints` this week.

2 files changed, 4 insertions, 6 deletions

diff --git a/src/libsyntax_ext/deriving/custom.rs b/src/libsyntax_ext/deriving/custom.rs
index 5fd5e299488..76da1746a03 100644
--- a/src/libsyntax_ext/deriving/custom.rs
+++ b/src/libsyntax_ext/deriving/custom.rs
@@ -22,11 +22,9 @@ struct MarkAttrs<'a>(&'a [ast::Name]);
 
 impl<'a> Visitor<'a> for MarkAttrs<'a> {
     fn visit_attribute(&mut self, attr: &Attribute) {
-        if let Some(name) = attr.name() {
-            if self.0.contains(&name) {
-                mark_used(attr);
-                mark_known(attr);
-            }
+        if self.0.contains(&attr.name()) {
+            mark_used(attr);
+            mark_known(attr);
         }
     }
 
diff --git a/src/libsyntax_ext/deriving/generic/mod.rs b/src/libsyntax_ext/deriving/generic/mod.rs
index becd70149fd..80f65957c39 100644
--- a/src/libsyntax_ext/deriving/generic/mod.rs
+++ b/src/libsyntax_ext/deriving/generic/mod.rs
@@ -472,7 +472,7 @@ impl<'a> TraitDef<'a> {
                 attrs.extend(item.attrs
                     .iter()
                     .filter(|a| {
-                        a.name().is_some() && match &*a.name().unwrap().as_str() {
+                        match &*a.name().as_str() {
                             "allow" | "warn" | "deny" | "forbid" | "stable" | "unstable" => true,
                             _ => false,
                         }