hygiene: Introduce a helper method for creating new expansions

Creating a fresh expansion and immediately generating a span from it is the most common scenario.

Also avoid allocating `allow_internal_unstable` lists for derive markers repeatedly.
And rename `ExpnInfo::with_unstable` to `ExpnInfo::allow_unstable`, seems to be a better fitting name.

3 files changed, 6 insertions, 7 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index cb4edee30cd..37d5885db60 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -721,6 +721,7 @@ pub struct ExtCtxt<'a> {
     pub resolver: &'a mut dyn Resolver,
     pub current_expansion: ExpansionData,
     pub expansions: FxHashMap<Span, Vec<String>>,
+    pub allow_derive_markers: Lrc<[Symbol]>,
 }
 
 impl<'a> ExtCtxt<'a> {
@@ -740,6 +741,7 @@ impl<'a> ExtCtxt<'a> {
                 directory_ownership: DirectoryOwnership::Owned { relative: None },
             },
             expansions: FxHashMap::default(),
+            allow_derive_markers: [sym::rustc_attrs, sym::structural_match][..].into(),
         }
     }
 
diff --git a/src/libsyntax/ext/derive.rs b/src/libsyntax/ext/derive.rs
index 11c1fceb7e7..1c15deab373 100644
--- a/src/libsyntax/ext/derive.rs
+++ b/src/libsyntax/ext/derive.rs
@@ -8,7 +8,6 @@ use crate::symbol::{Symbol, sym};
 use crate::errors::Applicability;
 
 use syntax_pos::Span;
-use syntax_pos::hygiene::{Mark, SyntaxContext};
 use rustc_data_structures::fx::FxHashSet;
 
 pub fn collect_derives(cx: &mut ExtCtxt<'_>, attrs: &mut Vec<ast::Attribute>) -> Vec<ast::Path> {
@@ -55,13 +54,11 @@ pub fn add_derived_markers<T>(cx: &mut ExtCtxt<'_>, span: Span, traits: &[ast::P
         names.insert(unwrap_or!(path.segments.get(0), continue).ident.name);
     }
 
-    let mark = Mark::fresh(cx.current_expansion.mark);
-    mark.set_expn_info(ExpnInfo::with_unstable(
+    let span = span.fresh_expansion(cx.current_expansion.mark, ExpnInfo::allow_unstable(
         ExpnKind::Macro(MacroKind::Derive, Symbol::intern(&pretty_name)), span,
-        cx.parse_sess.edition, &[sym::rustc_attrs, sym::structural_match],
+        cx.parse_sess.edition, cx.allow_derive_markers.clone(),
     ));
 
-    let span = span.with_ctxt(SyntaxContext::empty().apply_mark(mark));
     item.visit_attrs(|attrs| {
         if names.contains(&sym::Eq) && names.contains(&sym::PartialEq) {
             let meta = cx.meta_word(span, sym::structural_match);
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 2349382eb5e..39a8a7af2a3 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -362,7 +362,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 derives.reserve(traits.len());
                 invocations.reserve(traits.len());
                 for path in traits {
-                    let mark = Mark::fresh(self.cx.current_expansion.mark);
+                    let mark = Mark::fresh(self.cx.current_expansion.mark, None);
                     derives.push(mark);
                     invocations.push(Invocation {
                         kind: InvocationKind::Derive {
@@ -847,7 +847,7 @@ struct InvocationCollector<'a, 'b> {
 
 impl<'a, 'b> InvocationCollector<'a, 'b> {
     fn collect(&mut self, fragment_kind: AstFragmentKind, kind: InvocationKind) -> AstFragment {
-        let mark = Mark::fresh(self.cx.current_expansion.mark);
+        let mark = Mark::fresh(self.cx.current_expansion.mark, None);
         self.invocations.push(Invocation {
             kind,
             fragment_kind,