Auto merge of #43968 - petrochenkov:span2, r=michaelwoerister

Make fields of `Span` private

I actually tried to intern spans and benchmark the result<sup>*</sup>, and this was a prerequisite.
This kind of encapsulation will be a prerequisite for any other attempt to compress span's representation, so I decided to submit this change alone.

The issue #43088 seems relevant, but it looks like `SpanId` won't be able to reuse this interface, unless the tables are global (like interner that I tried) and are not a part of HIR.
r? @michaelwoerister anyway

<sup>*</sup> Interning means 2-3 times more space is required for a single span, but duplicates are free. In practice it turned out that duplicates are not *that* common, so more memory was wasted by interning rather than saved.

Author: bors

src/libproc_macro/lib.rs

@@ -89,10 +89,7 @@ impl FromStr for TokenStream {
             // notify the expansion info that it is unhygienic
             let mark = Mark::fresh(mark);
             mark.set_expn_info(expn_info);
-            let span = syntax_pos::Span {
-                ctxt: SyntaxContext::empty().apply_mark(mark),
-                ..call_site
-            };
+            let span = call_site.with_ctxt(SyntaxContext::empty().apply_mark(mark));
             let stream = parse::parse_stream_from_source_str(name, src, sess, Some(span));
             Ok(__internal::token_stream_wrap(stream))
         })
@@ -177,10 +174,10 @@ pub struct Span(syntax_pos::Span);
 #[unstable(feature = "proc_macro", issue = "38356")]
 impl Default for Span {
     fn default() -> Span {
-        ::__internal::with_sess(|(_, mark)| Span(syntax_pos::Span {
-            ctxt: SyntaxContext::empty().apply_mark(mark),
-            ..mark.expn_info().unwrap().call_site
-        }))
+        ::__internal::with_sess(|(_, mark)| {
+            let call_site = mark.expn_info().unwrap().call_site;
+            Span(call_site.with_ctxt(SyntaxContext::empty().apply_mark(mark)))
+        })
     }
 }
 
@@ -570,7 +567,7 @@ impl TokenTree {
                 }).into();
             },
             TokenNode::Term(symbol) => {
-                let ident = ast::Ident { name: symbol.0, ctxt: self.span.0.ctxt };
+                let ident = ast::Ident { name: symbol.0, ctxt: self.span.0.ctxt() };
                 let token =
                     if symbol.0.as_str().starts_with("'") { Lifetime(ident) } else { Ident(ident) };
                 return TokenTree::Token(self.span.0, token).into();

src/librustc/hir/lowering.rs

@@ -425,8 +425,7 @@ impl<'a> LoweringContext<'a> {
         Symbol::gensym(s)
     }
 
-    fn allow_internal_unstable(&self, reason: CompilerDesugaringKind, mut span: Span)
-        -> Span
+    fn allow_internal_unstable(&self, reason: CompilerDesugaringKind, span: Span) -> Span
     {
         let mark = Mark::fresh(Mark::root());
         mark.set_expn_info(codemap::ExpnInfo {
@@ -438,8 +437,7 @@ impl<'a> LoweringContext<'a> {
                 allow_internal_unsafe: false,
             },
         });
-        span.ctxt = SyntaxContext::empty().apply_mark(mark);
-        span
+        span.with_ctxt(SyntaxContext::empty().apply_mark(mark))
     }
 
     fn with_catch_scope<T, F>(&mut self, catch_id: NodeId, f: F) -> T
@@ -613,7 +611,7 @@ impl<'a> LoweringContext<'a> {
             TyKind::Slice(ref ty) => hir::TySlice(self.lower_ty(ty)),
             TyKind::Ptr(ref mt) => hir::TyPtr(self.lower_mt(mt)),
             TyKind::Rptr(ref region, ref mt) => {
-                let span = Span { hi: t.span.lo, ..t.span };
+                let span = t.span.with_hi(t.span.lo());
                 let lifetime = match *region {
                     Some(ref lt) => self.lower_lifetime(lt),
                     None => self.elided_lifetime(span)
@@ -1237,7 +1235,7 @@ impl<'a> LoweringContext<'a> {
             name: self.lower_ident(match f.ident {
                 Some(ident) => ident,
                 // FIXME(jseyfried) positional field hygiene
-                None => Ident { name: Symbol::intern(&index.to_string()), ctxt: f.span.ctxt },
+                None => Ident { name: Symbol::intern(&index.to_string()), ctxt: f.span.ctxt() },
             }),
             vis: self.lower_visibility(&f.vis, None),
             ty: self.lower_ty(&f.ty),