syntax_pos: NO_EXPANSION/SyntaxContext::empty() -> SyntaxContext::root()

For consistency with `ExpnId::root`.

Also introduce a helper `Span::with_root_ctxt` for creating spans with `SyntaxContext::root()` context

src/librustc/ich/hcx.rs

@@ -350,7 +350,7 @@ impl<'a> HashStable<StableHashingContext<'a>> for Span {
         let line_col_len = col | line | len;
         std_hash::Hash::hash(&line_col_len, hasher);
 
-        if span.ctxt == SyntaxContext::empty() {
+        if span.ctxt == SyntaxContext::root() {
             TAG_NO_EXPANSION.hash_stable(hcx, hasher);
         } else {
             TAG_EXPANSION.hash_stable(hcx, hasher);

src/librustc/ty/query/on_disk_cache.rs

@@ -592,7 +592,7 @@ impl<'a, 'tcx> SpecializedDecoder<Span> for CacheDecoder<'a, 'tcx> {
         // `SyntaxContextData::prev_ctxt` or `SyntaxContextData::opaque`. These things
         // don't seem to be used after HIR lowering, so everything should be fine
         // as long as incremental compilation does not kick in before that.
-        let location = || Span::new(lo, hi, SyntaxContext::empty());
+        let location = || Span::with_root_ctxt(lo, hi);
         let recover_from_expn_info = |this: &Self, expn_info, pos| {
             let span = location().fresh_expansion(ExpnId::root(), expn_info);
             this.synthetic_expansion_infos.borrow_mut().insert(pos, span.ctxt());
@@ -816,7 +816,7 @@ where
         col_lo.encode(self)?;
         len.encode(self)?;
 
-        if span_data.ctxt == SyntaxContext::empty() {
+        if span_data.ctxt == SyntaxContext::root() {
             TAG_NO_EXPANSION_INFO.encode(self)
         } else {
             let (expn_id, expn_info) = span_data.ctxt.outer_expn_with_info();

src/librustc_errors/lib.rs

@@ -43,8 +43,7 @@ use syntax_pos::{BytePos,
                  SourceFile,
                  FileName,
                  MultiSpan,
-                 Span,
-                 NO_EXPANSION};
+                 Span};
 
 /// Indicates the confidence in the correctness of a suggestion.
 ///
@@ -189,7 +188,7 @@ impl CodeSuggestion {
             // Find the bounding span.
             let lo = substitution.parts.iter().map(|part| part.span.lo()).min().unwrap();
             let hi = substitution.parts.iter().map(|part| part.span.hi()).min().unwrap();
-            let bounding_span = Span::new(lo, hi, NO_EXPANSION);
+            let bounding_span = Span::with_root_ctxt(lo, hi);
             let lines = cm.span_to_lines(bounding_span).unwrap();
             assert!(!lines.lines.is_empty());
 

src/librustc_metadata/cstore_impl.rs

@@ -35,7 +35,7 @@ use syntax::ext::proc_macro::BangProcMacro;
 use syntax::parse::source_file_to_stream;
 use syntax::parse::parser::emit_unclosed_delims;
 use syntax::symbol::{Symbol, sym};
-use syntax_pos::{Span, NO_EXPANSION, FileName};
+use syntax_pos::{Span, FileName};
 use rustc_data_structures::bit_set::BitSet;
 
 macro_rules! provide {
@@ -443,7 +443,7 @@ impl cstore::CStore {
         let source_name = FileName::Macros(macro_full_name);
 
         let source_file = sess.parse_sess.source_map().new_source_file(source_name, def.body);
-        let local_span = Span::new(source_file.start_pos, source_file.end_pos, NO_EXPANSION);
+        let local_span = Span::with_root_ctxt(source_file.start_pos, source_file.end_pos);
         let (body, mut errors) = source_file_to_stream(&sess.parse_sess, source_file, None);
         emit_unclosed_delims(&mut errors, &sess.diagnostic());
 

src/librustc_metadata/decoder.rs

@@ -32,7 +32,7 @@ use syntax::source_map;
 use syntax::symbol::{Symbol, sym};
 use syntax::ext::base::{MacroKind, SyntaxExtension};
 use syntax::ext::hygiene::ExpnId;
-use syntax_pos::{self, Span, BytePos, Pos, DUMMY_SP, NO_EXPANSION};
+use syntax_pos::{self, Span, BytePos, Pos, DUMMY_SP};
 use log::debug;
 
 pub struct DecodeContext<'a, 'tcx> {
@@ -344,7 +344,7 @@ impl<'a, 'tcx> SpecializedDecoder<Span> for DecodeContext<'a, 'tcx> {
         let hi = (hi + source_file.translated_source_file.start_pos)
                  - source_file.original_start_pos;
 
-        Ok(Span::new(lo, hi, NO_EXPANSION))
+        Ok(Span::with_root_ctxt(lo, hi))
     }
 }
 

src/librustc_resolve/lib.rs

@@ -1430,7 +1430,7 @@ impl<'a> Resolver<'a> {
         }
         let (general_span, modern_span) = if ident.name == kw::SelfUpper {
             // FIXME(jseyfried) improve `Self` hygiene
-            let empty_span = ident.span.with_ctxt(SyntaxContext::empty());
+            let empty_span = ident.span.with_ctxt(SyntaxContext::root());
             (empty_span, empty_span)
         } else if ns == TypeNS {
             let modern_span = ident.span.modern();

src/libsyntax/ext/base.rs

@@ -762,7 +762,7 @@ impl<'a> ExtCtxt<'a> {
         }
     }
     pub fn backtrace(&self) -> SyntaxContext {
-        SyntaxContext::empty().apply_mark(self.current_expansion.id)
+        SyntaxContext::root().apply_mark(self.current_expansion.id)
     }
 
     /// Returns span for the macro which originally caused the current expansion to happen.

src/libsyntax/ext/expand.rs

@@ -759,7 +759,7 @@ impl<'a> Parser<'a> {
             let msg = format!("macro expansion ignores token `{}` and any following",
                               self.this_token_to_string());
             // Avoid emitting backtrace info twice.
-            let def_site_span = self.token.span.with_ctxt(SyntaxContext::empty());
+            let def_site_span = self.token.span.with_ctxt(SyntaxContext::root());
             let mut err = self.diagnostic().struct_span_err(def_site_span, &msg);
             err.span_label(span, "caused by the macro expansion here");
             let msg = format!(

src/libsyntax/ext/proc_macro_server.rs

@@ -365,7 +365,7 @@ impl<'a> Rustc<'a> {
         let location = cx.current_expansion.id.expn_info().unwrap().call_site;
         let to_span = |transparency| {
             location.with_ctxt(
-                SyntaxContext::empty()
+                SyntaxContext::root()
                     .apply_mark_with_transparency(cx.current_expansion.id, transparency),
             )
         };

src/libsyntax/parse/lexer/mod.rs

@@ -4,7 +4,7 @@ use crate::symbol::{sym, Symbol};
 use crate::parse::unescape_error_reporting::{emit_unescape_error, push_escaped_char};
 
 use errors::{FatalError, DiagnosticBuilder};
-use syntax_pos::{BytePos, Pos, Span, NO_EXPANSION};
+use syntax_pos::{BytePos, Pos, Span};
 use rustc_lexer::Base;
 use rustc_lexer::unescape;
 
@@ -84,7 +84,7 @@ impl<'a> StringReader<'a> {
 
 
     fn mk_sp(&self, lo: BytePos, hi: BytePos) -> Span {
-        self.override_span.unwrap_or_else(|| Span::new(lo, hi, NO_EXPANSION))
+        self.override_span.unwrap_or_else(|| Span::with_root_ctxt(lo, hi))
     }
 
     /// Returns the next token, including trivia like whitespace or comments.

src/libsyntax/parse/lexer/tests.rs

@@ -9,7 +9,7 @@ use crate::diagnostics::plugin::ErrorMap;
 use crate::with_default_globals;
 use std::io;
 use std::path::PathBuf;
-use syntax_pos::{BytePos, Span, NO_EXPANSION, edition::Edition};
+use syntax_pos::{BytePos, Span, edition::Edition};
 use rustc_data_structures::fx::{FxHashSet, FxHashMap};
 use rustc_data_structures::sync::{Lock, Once};
 
@@ -61,7 +61,7 @@ fn t1() {
         let tok1 = string_reader.next_token();
         let tok2 = Token::new(
             mk_ident("fn"),
-            Span::new(BytePos(21), BytePos(23), NO_EXPANSION),
+            Span::with_root_ctxt(BytePos(21), BytePos(23)),
         );
         assert_eq!(tok1.kind, tok2.kind);
         assert_eq!(tok1.span, tok2.span);
@@ -71,7 +71,7 @@ fn t1() {
         assert_eq!(string_reader.pos.clone(), BytePos(28));
         let tok4 = Token::new(
             mk_ident("main"),
-            Span::new(BytePos(24), BytePos(28), NO_EXPANSION),
+            Span::with_root_ctxt(BytePos(24), BytePos(28)),
         );
         assert_eq!(tok3.kind, tok4.kind);
         assert_eq!(tok3.span, tok4.span);

src/libsyntax/parse/lexer/unicode_chars.rs

@@ -3,7 +3,7 @@
 
 use super::StringReader;
 use errors::{Applicability, DiagnosticBuilder};
-use syntax_pos::{BytePos, Pos, Span, NO_EXPANSION, symbol::kw};
+use syntax_pos::{BytePos, Pos, Span, symbol::kw};
 use crate::parse::token;
 
 #[rustfmt::skip] // for line breaks
@@ -343,7 +343,7 @@ crate fn check_for_substitution<'a>(
         None => return None,
     };
 
-    let span = Span::new(pos, pos + Pos::from_usize(ch.len_utf8()), NO_EXPANSION);
+    let span = Span::with_root_ctxt(pos, pos + Pos::from_usize(ch.len_utf8()));
 
     let (ascii_name, token) = match ASCII_ARRAY.iter().find(|&&(c, _, _)| c == ascii_char) {
         Some((_ascii_char, ascii_name, token)) => (ascii_name, token),
@@ -362,10 +362,9 @@ crate fn check_for_substitution<'a>(
             ascii_char, ascii_name
         );
         err.span_suggestion(
-            Span::new(
+            Span::with_root_ctxt(
                 pos,
                 pos + Pos::from_usize('“'.len_utf8() + s.len() + '”'.len_utf8()),
-                NO_EXPANSION,
             ),
             &msg,
             format!("\"{}\"", s),

src/libsyntax/parse/tests.rs

@@ -12,7 +12,7 @@ use crate::symbol::{kw, sym};
 use crate::tests::{matches_codepattern, string_to_stream, with_error_checking_parse};
 use crate::tokenstream::{DelimSpan, TokenTree, TokenStream};
 use crate::with_default_globals;
-use syntax_pos::{Span, BytePos, Pos, NO_EXPANSION};
+use syntax_pos::{Span, BytePos, Pos};
 
 use std::path::PathBuf;
 
@@ -27,7 +27,7 @@ fn parse_item_from_source_str(name: FileName, source: String, sess: &ParseSess)
 
 // produce a syntax_pos::span
 fn sp(a: u32, b: u32) -> Span {
-    Span::new(BytePos(a), BytePos(b), NO_EXPANSION)
+    Span::with_root_ctxt(BytePos(a), BytePos(b))
 }
 
 /// Parse a string, return an expr

src/libsyntax/source_map/tests.rs

@@ -91,7 +91,7 @@ fn t6() {
 fn t7() {
     // Test span_to_lines for a span ending at the end of source_file
     let sm = init_source_map();
-    let span = Span::new(BytePos(12), BytePos(23), NO_EXPANSION);
+    let span = Span::with_root_ctxt(BytePos(12), BytePos(23));
     let file_lines = sm.span_to_lines(span).unwrap();
 
     assert_eq!(file_lines.file.name, PathBuf::from("blork.rs").into());
@@ -107,7 +107,7 @@ fn span_from_selection(input: &str, selection: &str) -> Span {
     assert_eq!(input.len(), selection.len());
     let left_index = selection.find('~').unwrap() as u32;
     let right_index = selection.rfind('~').map(|x|x as u32).unwrap_or(left_index);
-    Span::new(BytePos(left_index), BytePos(right_index + 1), NO_EXPANSION)
+    Span::with_root_ctxt(BytePos(left_index), BytePos(right_index + 1))
 }
 
 /// Tests span_to_snippet and span_to_lines for a span converting 3
@@ -137,7 +137,7 @@ fn span_to_snippet_and_lines_spanning_multiple_lines() {
 fn t8() {
     // Test span_to_snippet for a span ending at the end of source_file
     let sm = init_source_map();
-    let span = Span::new(BytePos(12), BytePos(23), NO_EXPANSION);
+    let span = Span::with_root_ctxt(BytePos(12), BytePos(23));
     let snippet = sm.span_to_snippet(span);
 
     assert_eq!(snippet, Ok("second line".to_string()));
@@ -147,7 +147,7 @@ fn t8() {
 fn t9() {
     // Test span_to_str for a span ending at the end of source_file
     let sm = init_source_map();
-    let span = Span::new(BytePos(12), BytePos(23), NO_EXPANSION);
+    let span = Span::with_root_ctxt(BytePos(12), BytePos(23));
     let sstr =  sm.span_to_string(span);
 
     assert_eq!(sstr, "blork.rs:2:1: 2:12");
@@ -198,10 +198,9 @@ impl SourceMapExtension for SourceMap {
             let lo = hi + offset;
             hi = lo + substring.len();
             if i == n {
-                let span = Span::new(
+                let span = Span::with_root_ctxt(
                     BytePos(lo as u32 + file.start_pos.0),
                     BytePos(hi as u32 + file.start_pos.0),
-                    NO_EXPANSION,
                 );
                 assert_eq!(&self.span_to_snippet(span).unwrap()[..],
                         substring);

src/libsyntax/tests.rs

@@ -9,7 +9,7 @@ use crate::with_default_globals;
 use errors::emitter::EmitterWriter;
 use errors::Handler;
 use rustc_data_structures::sync::Lrc;
-use syntax_pos::{BytePos, NO_EXPANSION, Span, MultiSpan};
+use syntax_pos::{BytePos, Span, MultiSpan};
 
 use std::io;
 use std::io::prelude::*;
@@ -169,7 +169,7 @@ fn make_span(file_text: &str, start: &Position, end: &Position) -> Span {
     let start = make_pos(file_text, start);
     let end = make_pos(file_text, end) + end.string.len(); // just after matching thing ends
     assert!(start <= end);
-    Span::new(BytePos(start as u32), BytePos(end as u32), NO_EXPANSION)
+    Span::with_root_ctxt(BytePos(start as u32), BytePos(end as u32))
 }
 
 fn make_pos(file_text: &str, pos: &Position) -> usize {

src/libsyntax/tokenstream/tests.rs

@@ -3,14 +3,14 @@ use super::*;
 use crate::ast::Name;
 use crate::with_default_globals;
 use crate::tests::string_to_stream;
-use syntax_pos::{Span, BytePos, NO_EXPANSION};
+use syntax_pos::{Span, BytePos};
 
 fn string_to_ts(string: &str) -> TokenStream {
     string_to_stream(string.to_owned())
 }
 
 fn sp(a: u32, b: u32) -> Span {
-    Span::new(BytePos(a), BytePos(b), NO_EXPANSION)
+    Span::with_root_ctxt(BytePos(a), BytePos(b))
 }
 
 #[test]

src/libsyntax_ext/global_allocator.rs

@@ -29,7 +29,7 @@ pub fn expand(
     };
 
     // Generate a bunch of new items using the AllocFnFactory
-    let span = item.span.with_ctxt(SyntaxContext::empty().apply_mark(ecx.current_expansion.id));
+    let span = item.span.with_ctxt(SyntaxContext::root().apply_mark(ecx.current_expansion.id));
     let f = AllocFnFactory {
         span,
         kind: AllocatorKind::Global,

src/libsyntax_ext/test.rs

@@ -29,7 +29,7 @@ pub fn expand_test_case(
 
     if !ecx.ecfg.should_test { return vec![]; }
 
-    let sp = attr_sp.with_ctxt(SyntaxContext::empty().apply_mark(ecx.current_expansion.id));
+    let sp = attr_sp.with_ctxt(SyntaxContext::root().apply_mark(ecx.current_expansion.id));
     let mut item = anno_item.expect_item();
     item = item.map(|mut item| {
         item.vis = respan(item.vis.span, ast::VisibilityKind::Public);
@@ -93,7 +93,7 @@ pub fn expand_test_or_bench(
         return vec![Annotatable::Item(item)];
     }
 
-    let ctxt = SyntaxContext::empty().apply_mark(cx.current_expansion.id);
+    let ctxt = SyntaxContext::root().apply_mark(cx.current_expansion.id);
     let (sp, attr_sp) = (item.span.with_ctxt(ctxt), attr_sp.with_ctxt(ctxt));
 
     // Gensym "test" so we can extern crate without conflicting with any local names

src/libsyntax_pos/hygiene.rs

@@ -246,7 +246,7 @@ impl HygieneData {
 
     fn marks(&self, mut ctxt: SyntaxContext) -> Vec<(ExpnId, Transparency)> {
         let mut marks = Vec::new();
-        while ctxt != SyntaxContext::empty() {
+        while ctxt != SyntaxContext::root() {
             marks.push((self.outer_expn(ctxt), self.outer_transparency(ctxt)));
             ctxt = self.parent_ctxt(ctxt);
         }
@@ -286,14 +286,14 @@ impl HygieneData {
         }
 
         let call_site_ctxt =
-            self.expn_info(expn_id).map_or(SyntaxContext::empty(), |info| info.call_site.ctxt());
+            self.expn_info(expn_id).map_or(SyntaxContext::root(), |info| info.call_site.ctxt());
         let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
             self.modern(call_site_ctxt)
         } else {
             self.modern_and_legacy(call_site_ctxt)
         };
 
-        if call_site_ctxt == SyntaxContext::empty() {
+        if call_site_ctxt == SyntaxContext::root() {
             return self.apply_mark_internal(ctxt, expn_id, transparency);
         }
 
@@ -400,7 +400,7 @@ pub fn update_dollar_crate_names(mut get_name: impl FnMut(SyntaxContext) -> Symb
 
 impl SyntaxContext {
     #[inline]
-    pub const fn empty() -> Self {
+    pub const fn root() -> Self {
         SyntaxContext(0)
     }
 
@@ -615,7 +615,7 @@ impl Span {
     pub fn fresh_expansion(self, parent: ExpnId, expn_info: ExpnInfo) -> Span {
         HygieneData::with(|data| {
             let expn_id = data.fresh_expn(parent, Some(expn_info));
-            self.with_ctxt(data.apply_mark(SyntaxContext::empty(), expn_id))
+            self.with_ctxt(data.apply_mark(SyntaxContext::root(), expn_id))
         })
     }
 }
@@ -775,6 +775,6 @@ impl Encodable for SyntaxContext {
 
 impl Decodable for SyntaxContext {
     fn decode<D: Decoder>(_: &mut D) -> Result<SyntaxContext, D::Error> {
-        Ok(SyntaxContext::empty()) // FIXME(jseyfried) intercrate hygiene
+        Ok(SyntaxContext::root()) // FIXME(jseyfried) intercrate hygiene
     }
 }

src/libsyntax_pos/lib.rs

@@ -291,7 +291,12 @@ impl Span {
     /// Returns `true` if this span comes from a macro or desugaring.
     #[inline]
     pub fn from_expansion(self) -> bool {
-        self.ctxt() != SyntaxContext::empty()
+        self.ctxt() != SyntaxContext::root()
+    }
+
+    #[inline]
+    pub fn with_root_ctxt(lo: BytePos, hi: BytePos) -> Span {
+        Span::new(lo, hi, SyntaxContext::root())
     }
 
     /// Returns a new span representing an empty span at the beginning of this span
@@ -474,9 +479,9 @@ impl Span {
         // Return the macro span on its own to avoid weird diagnostic output. It is preferable to
         // have an incomplete span than a completely nonsensical one.
         if span_data.ctxt != end_data.ctxt {
-            if span_data.ctxt == SyntaxContext::empty() {
+            if span_data.ctxt == SyntaxContext::root() {
                 return end;
-            } else if end_data.ctxt == SyntaxContext::empty() {
+            } else if end_data.ctxt == SyntaxContext::root() {
                 return self;
             }
             // Both spans fall within a macro.
@@ -485,7 +490,7 @@ impl Span {
         Span::new(
             cmp::min(span_data.lo, end_data.lo),
             cmp::max(span_data.hi, end_data.hi),
-            if span_data.ctxt == SyntaxContext::empty() { end_data.ctxt } else { span_data.ctxt },
+            if span_data.ctxt == SyntaxContext::root() { end_data.ctxt } else { span_data.ctxt },
         )
     }
 
@@ -496,7 +501,7 @@ impl Span {
         Span::new(
             span.hi,
             end.lo,
-            if end.ctxt == SyntaxContext::empty() { end.ctxt } else { span.ctxt },
+            if end.ctxt == SyntaxContext::root() { end.ctxt } else { span.ctxt },
         )
     }
 
@@ -507,7 +512,7 @@ impl Span {
         Span::new(
             span.lo,
             end.lo,
-            if end.ctxt == SyntaxContext::empty() { end.ctxt } else { span.ctxt },
+            if end.ctxt == SyntaxContext::root() { end.ctxt } else { span.ctxt },
         )
     }
 
@@ -617,7 +622,7 @@ impl rustc_serialize::UseSpecializedDecodable for Span {
         d.read_struct("Span", 2, |d| {
             let lo = d.read_struct_field("lo", 0, Decodable::decode)?;
             let hi = d.read_struct_field("hi", 1, Decodable::decode)?;
-            Ok(Span::new(lo, hi, NO_EXPANSION))
+            Ok(Span::with_root_ctxt(lo, hi))
         })
     }
 }
@@ -761,8 +766,6 @@ impl From<Vec<Span>> for MultiSpan {
     }
 }
 
-pub const NO_EXPANSION: SyntaxContext = SyntaxContext::empty();
-
 /// Identifies an offset of a multi-byte character in a `SourceFile`.
 #[derive(Copy, Clone, RustcEncodable, RustcDecodable, Eq, PartialEq, Debug)]
 pub struct MultiByteChar {