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 https://github.com/rust-lang/rust/issues/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.

1 files changed, 3 insertions, 7 deletions

diff --git a/src/libsyntax/tokenstream.rs b/src/libsyntax/tokenstream.rs
index 747bc7b4385..870f54e4396 100644
--- a/src/libsyntax/tokenstream.rs
+++ b/src/libsyntax/tokenstream.rs
@@ -59,7 +59,7 @@ impl Delimited {
         let open_span = if span == DUMMY_SP {
             DUMMY_SP
         } else {
-            Span { hi: span.lo + BytePos(self.delim.len() as u32), ..span }
+            span.with_hi(span.lo() + BytePos(self.delim.len() as u32))
         };
         TokenTree::Token(open_span, self.open_token())
     }
@@ -69,7 +69,7 @@ impl Delimited {
         let close_span = if span == DUMMY_SP {
             DUMMY_SP
         } else {
-            Span { lo: span.hi - BytePos(self.delim.len() as u32), ..span }
+            span.with_lo(span.hi() - BytePos(self.delim.len() as u32))
         };
         TokenTree::Token(close_span, self.close_token())
     }
@@ -602,11 +602,7 @@ mod tests {
     }
 
     fn sp(a: u32, b: u32) -> Span {
-        Span {
-            lo: BytePos(a),
-            hi: BytePos(b),
-            ctxt: NO_EXPANSION,
-        }
+        Span::new(BytePos(a), BytePos(b), NO_EXPANSION)
     }
 
     #[test]