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.

5 files changed, 18 insertions, 40 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,
diff --git a/src/libsyntax/std_inject.rs b/src/libsyntax/std_inject.rs
index 81f9ff9b661..d86b76f71ec 100644
--- a/src/libsyntax/std_inject.rs
+++ b/src/libsyntax/std_inject.rs
@@ -1,7 +1,7 @@
 use crate::ast;
 use crate::attr;
 use crate::edition::Edition;
-use crate::ext::hygiene::{Mark, SyntaxContext, MacroKind};
+use crate::ext::hygiene::{Mark, MacroKind};
 use crate::symbol::{Ident, Symbol, kw, sym};
 use crate::source_map::{ExpnInfo, ExpnKind, dummy_spanned, respan};
 use crate::ptr::P;
@@ -9,19 +9,7 @@ use crate::tokenstream::TokenStream;
 
 use std::cell::Cell;
 use std::iter;
-use syntax_pos::{DUMMY_SP, Span};
-
-/// Craft a span that will be ignored by the stability lint's
-/// call to source_map's `is_internal` check.
-/// The expanded code uses the unstable `#[prelude_import]` attribute.
-fn ignored_span(sp: Span, edition: Edition) -> Span {
-    let mark = Mark::fresh(Mark::root());
-    mark.set_expn_info(ExpnInfo::with_unstable(
-        ExpnKind::Macro(MacroKind::Attr, Symbol::intern("std_inject")), sp, edition,
-        &[sym::prelude_import],
-    ));
-    sp.with_ctxt(SyntaxContext::empty().apply_mark(mark))
-}
+use syntax_pos::DUMMY_SP;
 
 pub fn injected_crate_name() -> Option<&'static str> {
     INJECTED_CRATE_NAME.with(|name| name.get())
@@ -87,7 +75,11 @@ pub fn maybe_inject_crates_ref(
 
     INJECTED_CRATE_NAME.with(|opt_name| opt_name.set(Some(name)));
 
-    let span = ignored_span(DUMMY_SP, edition);
+    let span = DUMMY_SP.fresh_expansion(Mark::root(), ExpnInfo::allow_unstable(
+        ExpnKind::Macro(MacroKind::Attr, sym::std_inject), DUMMY_SP, edition,
+        [sym::prelude_import][..].into(),
+    ));
+
     krate.module.items.insert(0, P(ast::Item {
         attrs: vec![ast::Attribute {
             style: ast::AttrStyle::Outer,
diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
index 7ec7bb6ff45..799d64a9962 100644
--- a/src/libsyntax/test.rs
+++ b/src/libsyntax/test.rs
@@ -43,7 +43,6 @@ struct TestCtxt<'a> {
     test_cases: Vec<Test>,
     reexport_test_harness_main: Option<Symbol>,
     is_libtest: bool,
-    ctxt: SyntaxContext,
     features: &'a Features,
     test_runner: Option<ast::Path>,
 
@@ -259,8 +258,6 @@ fn generate_test_harness(sess: &ParseSess,
     let mut cleaner = EntryPointCleaner { depth: 0 };
     cleaner.visit_crate(krate);
 
-    let mark = Mark::fresh(Mark::root());
-
     let mut econfig = ExpansionConfig::default("test".to_string());
     econfig.features = Some(features);
 
@@ -274,16 +271,10 @@ fn generate_test_harness(sess: &ParseSess,
         is_libtest: attr::find_crate_name(&krate.attrs)
             .map(|s| s == sym::test).unwrap_or(false),
         toplevel_reexport: None,
-        ctxt: SyntaxContext::empty().apply_mark(mark),
         features,
         test_runner
     };
 
-    mark.set_expn_info(ExpnInfo::with_unstable(
-        ExpnKind::Macro(MacroKind::Attr, sym::test_case), DUMMY_SP, sess.edition,
-        &[sym::main, sym::test, sym::rustc_attrs],
-    ));
-
     TestHarnessGenerator {
         cx,
         tests: Vec::new(),
@@ -291,13 +282,6 @@ fn generate_test_harness(sess: &ParseSess,
     }.visit_crate(krate);
 }
 
-/// Craft a span that will be ignored by the stability lint's
-/// call to source_map's `is_internal` check.
-/// The expanded code calls some unstable functions in the test crate.
-fn ignored_span(cx: &TestCtxt<'_>, sp: Span) -> Span {
-    sp.with_ctxt(cx.ctxt)
-}
-
 enum HasTestSignature {
     Yes,
     No(BadTestSignature),
@@ -314,12 +298,15 @@ enum BadTestSignature {
 /// Creates a function item for use as the main function of a test build.
 /// This function will call the `test_runner` as specified by the crate attribute
 fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
-    // Writing this out by hand with 'ignored_span':
+    // Writing this out by hand:
     //        pub fn main() {
     //            #![main]
     //            test::test_main_static(&[..tests]);
     //        }
-    let sp = ignored_span(cx, DUMMY_SP);
+    let sp = DUMMY_SP.fresh_expansion(Mark::root(), ExpnInfo::allow_unstable(
+        ExpnKind::Macro(MacroKind::Attr, sym::test_case), DUMMY_SP, cx.ext_cx.parse_sess.edition,
+        [sym::main, sym::test, sym::rustc_attrs][..].into(),
+    ));
     let ecx = &cx.ext_cx;
     let test_id = Ident::with_empty_ctxt(sym::test);