Auto merge of #62069 - Centril:rollup-m8n4uw7, r=Centril

Rollup of 5 pull requests

Successful merges:

 - #62047 (Trigger `unused_attribute` lint on `#[cfg_attr($pred,)]`)
 - #62049 (Fix one missing `dyn`.)
 - #62051 (Lint empty `#[derive()]` as unused attribute.)
 - #62057 (Deny explicit_outlives_requirements in the compiler)
 - #62068 (Fix meta-variable binding errors in macros)

Failed merges:

r? @ghost

3 files changed, 17 insertions, 20 deletions

diff --git a/src/libsyntax/config.rs b/src/libsyntax/config.rs
index 3b42e1de614..1ab367f73c1 100644
--- a/src/libsyntax/config.rs
+++ b/src/libsyntax/config.rs
@@ -91,10 +91,10 @@ impl<'a> StripUnconfigured<'a> {
     /// is in the original source file. Gives a compiler error if the syntax of
     /// the attribute is incorrect.
     fn process_cfg_attr(&mut self, attr: ast::Attribute) -> Vec<ast::Attribute> {
-        if !attr.check_name(sym::cfg_attr) {
+        if attr.path != sym::cfg_attr {
             return vec![attr];
         }
-        if attr.tokens.len() == 0 {
+        if attr.tokens.is_empty() {
             self.sess.span_diagnostic
                 .struct_span_err(
                     attr.span,
@@ -108,7 +108,7 @@ impl<'a> StripUnconfigured<'a> {
                        <https://doc.rust-lang.org/reference/conditional-compilation.html\
                        #the-cfg_attr-attribute>")
                 .emit();
-            return Vec::new();
+            return vec![];
         }
 
         let (cfg_predicate, expanded_attrs) = match attr.parse(self.sess, |parser| {
@@ -133,17 +133,18 @@ impl<'a> StripUnconfigured<'a> {
             Ok(result) => result,
             Err(mut e) => {
                 e.emit();
-                return Vec::new();
+                return vec![];
             }
         };
 
-        // Check feature gate and lint on zero attributes in source. Even if the feature is gated,
-        // we still compute as if it wasn't, since the emitted error will stop compilation further
-        // along the compilation.
-        if expanded_attrs.len() == 0 {
-            // FIXME: Emit unused attribute lint here.
+        // Lint on zero attributes in source.
+        if expanded_attrs.is_empty() {
+            return vec![attr];
         }
 
+        // At this point we know the attribute is considered used.
+        attr::mark_used(&attr);
+
         if attr::cfg_matches(&cfg_predicate, self.sess, self.features) {
             // We call `process_cfg_attr` recursively in case there's a
             // `cfg_attr` inside of another `cfg_attr`. E.g.
@@ -159,7 +160,7 @@ impl<'a> StripUnconfigured<'a> {
             }))
             .collect()
         } else {
-            Vec::new()
+            vec![]
         }
     }
 
diff --git a/src/libsyntax/ext/derive.rs b/src/libsyntax/ext/derive.rs
index abc451c96ae..3b4243ed24f 100644
--- a/src/libsyntax/ext/derive.rs
+++ b/src/libsyntax/ext/derive.rs
@@ -30,10 +30,6 @@ pub fn collect_derives(cx: &mut ExtCtxt<'_>, attrs: &mut Vec<ast::Attribute>) ->
 
         match attr.parse_list(cx.parse_sess,
                               |parser| parser.parse_path_allowing_meta(PathStyle::Mod)) {
-            Ok(ref traits) if traits.is_empty() => {
-                cx.span_warn(attr.span, "empty trait list in `derive`");
-                false
-            }
             Ok(traits) => {
                 result.extend(traits);
                 true
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index cfd67575b6f..945cf36af46 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -98,9 +98,9 @@ macro_rules! ast_fragments {
                             }
                         });
                     }
-                    $($(AstFragment::$Kind(ast) => vis.$mut_visit_ast(ast),)*)*
+                    $($(AstFragment::$Kind(ast) => vis.$mut_visit_ast(ast),)?)*
                     $($(AstFragment::$Kind(ast) =>
-                        ast.flat_map_in_place(|ast| vis.$flat_map_ast_elt(ast)),)*)*
+                        ast.flat_map_in_place(|ast| vis.$flat_map_ast_elt(ast)),)?)*
                 }
             }
 
@@ -108,10 +108,10 @@ macro_rules! ast_fragments {
                 match *self {
                     AstFragment::OptExpr(Some(ref expr)) => visitor.visit_expr(expr),
                     AstFragment::OptExpr(None) => {}
-                    $($(AstFragment::$Kind(ref ast) => visitor.$visit_ast(ast),)*)*
+                    $($(AstFragment::$Kind(ref ast) => visitor.$visit_ast(ast),)?)*
                     $($(AstFragment::$Kind(ref ast) => for ast_elt in &ast[..] {
                         visitor.$visit_ast_elt(ast_elt);
-                    })*)*
+                    })?)*
                 }
             }
         }
@@ -122,10 +122,10 @@ macro_rules! ast_fragments {
             }
             $($(fn $mut_visit_ast(&mut self, ast: &mut $AstTy) {
                 visit_clobber(ast, |ast| self.expand_fragment(AstFragment::$Kind(ast)).$make_ast());
-            })*)*
+            })?)*
             $($(fn $flat_map_ast_elt(&mut self, ast_elt: <$AstTy as IntoIterator>::Item) -> $AstTy {
                 self.expand_fragment(AstFragment::$Kind(smallvec![ast_elt])).$make_ast()
-            })*)*
+            })?)*
         }
 
         impl<'a> MacResult for crate::ext::tt::macro_rules::ParserAnyMacro<'a> {