3 files changed, 27 insertions, 18 deletions
diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 3cd5464f357..263eb1ac7a4 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -29,16 +29,15 @@ pub struct UnmatchedBrace {
 }
 
 pub struct StringReader<'a> {
-    crate sess: &'a ParseSess,
-    /// The absolute offset within the source_map of the current character
-    crate pos: BytePos,
-    /// The current character (which has been read from self.pos)
-    crate source_file: Lrc<syntax_pos::SourceFile>,
+    sess: &'a ParseSess,
+    /// Initial position, read-only.
+    start_pos: BytePos,
+    /// The absolute offset within the source_map of the current character.
+    pos: BytePos,
     /// Stop reading src at this index.
-    crate end_src_index: usize,
+    end_src_index: usize,
     fatal_errs: Vec<DiagnosticBuilder<'a>>,
-    // cache a direct reference to the source text, so that we don't have to
-    // retrieve it via `self.source_file.src.as_ref().unwrap()` all the time.
+    /// Source text to tokenize.
     src: Lrc<String>,
     override_span: Option<Span>,
 }
@@ -56,8 +55,8 @@ impl<'a> StringReader<'a> {
 
         StringReader {
             sess,
+            start_pos: source_file.start_pos,
             pos: source_file.start_pos,
-            source_file,
             end_src_index: src.len(),
             src,
             fatal_errs: Vec::new(),
@@ -108,12 +107,12 @@ impl<'a> StringReader<'a> {
         let text: &str = &self.src[start_src_index..self.end_src_index];
 
         if text.is_empty() {
-            let span = self.mk_sp(self.source_file.end_pos, self.source_file.end_pos);
+            let span = self.mk_sp(self.pos, self.pos);
             return Ok(Token::new(token::Eof, span));
         }
 
         {
-            let is_beginning_of_file = self.pos == self.source_file.start_pos;
+            let is_beginning_of_file = self.pos == self.start_pos;
             if is_beginning_of_file {
                 if let Some(shebang_len) = rustc_lexer::strip_shebang(text) {
                     let start = self.pos;
@@ -533,7 +532,7 @@ impl<'a> StringReader<'a> {
 
     #[inline]
     fn src_index(&self, pos: BytePos) -> usize {
-        (pos - self.source_file.start_pos).to_usize()
+        (pos - self.start_pos).to_usize()
     }
 
     /// Slice of the source text from `start` up to but excluding `self.pos`,
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 7fda9158b4b..7096d6799e2 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -143,6 +143,7 @@ macro_rules! maybe_whole_expr {
                         $p.token.span, ExprKind::Block(block, None), ThinVec::new()
                     ));
                 }
+                // N.B: `NtIdent(ident)` is normalized to `Ident` in `fn bump`.
                 _ => {},
             };
         }
@@ -2756,12 +2757,7 @@ impl<'a> Parser<'a> {
                     // can't continue an expression after an ident
                     token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
                     token::Literal(..) | token::Pound => true,
-                    token::Interpolated(ref nt) => match **nt {
-                        token::NtIdent(..) | token::NtExpr(..) |
-                        token::NtBlock(..) | token::NtPath(..) => true,
-                        _ => false,
-                    },
-                    _ => false
+                    _ => t.is_whole_expr(),
                 };
                 let cannot_continue_expr = self.look_ahead(1, token_cannot_continue_expr);
                 if cannot_continue_expr {
@@ -3728,6 +3724,7 @@ impl<'a> Parser<'a> {
         self.token.is_path_start() // e.g. `MY_CONST`;
             || self.token == token::Dot // e.g. `.5` for recovery;
             || self.token.can_begin_literal_or_bool() // e.g. `42`.
+            || self.token.is_whole_expr()
     }
 
     // Helper function to decide whether to parse as ident binding
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 472e4b474d6..73adb5c947c 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -476,6 +476,19 @@ impl Token {
         false
     }
 
+    /// Would `maybe_whole_expr` in `parser.rs` return `Ok(..)`?
+    /// That is, is this a pre-parsed expression dropped into the token stream
+    /// (which happens while parsing the result of macro expansion)?
+    crate fn is_whole_expr(&self) -> bool {
+        if let Interpolated(ref nt) = self.kind {
+            if let NtExpr(_) | NtLiteral(_) | NtPath(_) | NtIdent(..) | NtBlock(_) = **nt {
+                return true;
+            }
+        }
+
+        false
+    }
+
     /// Returns `true` if the token is either the `mut` or `const` keyword.
     crate fn is_mutability(&self) -> bool {
         self.is_keyword(kw::Mut) ||