Audit uses of apply_mark in built-in macros

Replace them with equivalents of `Span::{def_site,call_site}` from proc macro API.
The new API is much less error prone and doesn't rely on macros having default transparency.

src/libsyntax/ext/base.rs

@@ -3,7 +3,7 @@ use crate::attr::{HasAttrs, Stability, Deprecation};
 use crate::source_map::SourceMap;
 use crate::edition::Edition;
 use crate::ext::expand::{self, AstFragment, Invocation};
-use crate::ext::hygiene::{ExpnId, SyntaxContext, Transparency};
+use crate::ext::hygiene::{ExpnId, Transparency};
 use crate::mut_visit::{self, MutVisitor};
 use crate::parse::{self, parser, DirectoryOwnership};
 use crate::parse::token;
@@ -760,23 +760,39 @@ impl<'a> ExtCtxt<'a> {
     pub fn call_site(&self) -> Span {
         self.current_expansion.id.expn_data().call_site
     }
-    pub fn backtrace(&self) -> SyntaxContext {
-        SyntaxContext::root().apply_mark(self.current_expansion.id)
+
+    /// Equivalent of `Span::def_site` from the proc macro API,
+    /// except that the location is taken from the span passed as an argument.
+    pub fn with_def_site_ctxt(&self, span: Span) -> Span {
+        span.with_ctxt_from_mark(self.current_expansion.id, Transparency::Opaque)
+    }
+
+    /// Equivalent of `Span::call_site` from the proc macro API,
+    /// except that the location is taken from the span passed as an argument.
+    pub fn with_call_site_ctxt(&self, span: Span) -> Span {
+        span.with_ctxt_from_mark(self.current_expansion.id, Transparency::Transparent)
+    }
+
+    /// Span with a context reproducing `macro_rules` hygiene (hygienic locals, unhygienic items).
+    /// FIXME: This should be eventually replaced either with `with_def_site_ctxt` (preferably),
+    /// or with `with_call_site_ctxt` (where necessary).
+    pub fn with_legacy_ctxt(&self, span: Span) -> Span {
+        span.with_ctxt_from_mark(self.current_expansion.id, Transparency::SemiTransparent)
     }
 
     /// Returns span for the macro which originally caused the current expansion to happen.
     ///
     /// Stops backtracing at include! boundary.
     pub fn expansion_cause(&self) -> Option<Span> {
-        let mut ctxt = self.backtrace();
+        let mut expn_id = self.current_expansion.id;
         let mut last_macro = None;
         loop {
-            let expn_data = ctxt.outer_expn_data();
+            let expn_data = expn_id.expn_data();
             // Stop going up the backtrace once include! is encountered
             if expn_data.is_root() || expn_data.kind.descr() == sym::include {
                 break;
             }
-            ctxt = expn_data.call_site.ctxt();
+            expn_id = expn_data.call_site.ctxt().outer_expn();
             last_macro = Some(expn_data.call_site);
         }
         last_macro
@@ -865,7 +881,7 @@ impl<'a> ExtCtxt<'a> {
         ast::Ident::from_str(st)
     }
     pub fn std_path(&self, components: &[Symbol]) -> Vec<ast::Ident> {
-        let def_site = DUMMY_SP.apply_mark(self.current_expansion.id);
+        let def_site = self.with_def_site_ctxt(DUMMY_SP);
         iter::once(Ident::new(kw::DollarCrate, def_site))
             .chain(components.iter().map(|&s| Ident::with_dummy_span(s)))
             .collect()

src/libsyntax/ext/expand.rs

@@ -565,7 +565,6 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         return fragment_kind.dummy(span);
                     }
                     let meta = ast::MetaItem { node: ast::MetaItemKind::Word, span, path };
-                    let span = span.with_ctxt(self.cx.backtrace());
                     let items = expander.expand(self.cx, span, &meta, item);
                     fragment_kind.expect_from_annotatables(items)
                 }

src/libsyntax/ext/proc_macro_server.rs

@@ -7,7 +7,6 @@ use crate::tokenstream::{self, DelimSpan, IsJoint::*, TokenStream, TreeAndJoint}
 use errors::{Diagnostic, DiagnosticBuilder};
 use rustc_data_structures::sync::Lrc;
 use syntax_pos::{BytePos, FileName, MultiSpan, Pos, SourceFile, Span};
-use syntax_pos::hygiene::{SyntaxContext, Transparency};
 use syntax_pos::symbol::{kw, sym, Symbol};
 
 use proc_macro::{Delimiter, Level, LineColumn, Spacing};
@@ -363,16 +362,10 @@ impl<'a> Rustc<'a> {
     pub fn new(cx: &'a ExtCtxt<'_>) -> Self {
         // No way to determine def location for a proc macro right now, so use call location.
         let location = cx.current_expansion.id.expn_data().call_site;
-        let to_span = |transparency| {
-            location.with_ctxt(
-                SyntaxContext::root()
-                    .apply_mark_with_transparency(cx.current_expansion.id, transparency),
-            )
-        };
         Rustc {
             sess: cx.parse_sess,
-            def_site: to_span(Transparency::Opaque),
-            call_site: to_span(Transparency::Transparent),
+            def_site: cx.with_def_site_ctxt(location),
+            call_site: cx.with_call_site_ctxt(location),
         }
     }