Use a span from the correct file for the inner span of a module

This basically only affects modules which are empty (or only contain comments).

Closes #26755

src/librustdoc/clean/mod.rs

@@ -1947,6 +1947,10 @@ impl Span {
 
 impl Clean<Span> for syntax::codemap::Span {
     fn clean(&self, cx: &DocContext) -> Span {
+        if *self == DUMMY_SP {
+            return Span::empty();
+        }
+
         let cm = cx.sess().codemap();
         let filename = cm.span_to_filename(*self);
         let lo = cm.lookup_char_pos(self.lo);

src/libsyntax/codemap.rs

@@ -894,7 +894,7 @@ impl CodeMap {
         FileMapAndBytePos {fm: fm, pos: offset}
     }
 
-    /// Converts an absolute BytePos to a CharPos relative to the filemap and above.
+    /// Converts an absolute BytePos to a CharPos relative to the filemap.
     pub fn bytepos_to_file_charpos(&self, bpos: BytePos) -> CharPos {
         let idx = self.lookup_filemap_idx(bpos);
         let files = self.files.borrow();

src/libsyntax/parse/lexer/mod.rs

@@ -231,6 +231,7 @@ impl<'a> StringReader<'a> {
             None => {
                 if self.is_eof() {
                     self.peek_tok = token::Eof;
+                    self.peek_span = codemap::mk_sp(self.filemap.end_pos, self.filemap.end_pos);
                 } else {
                     let start_bytepos = self.last_pos;
                     self.peek_tok = self.next_token_inner();

src/libsyntax/parse/mod.rs

@@ -11,7 +11,7 @@
 //! The main parser interface
 
 use ast;
-use codemap::{Span, CodeMap, FileMap};
+use codemap::{self, Span, CodeMap, FileMap};
 use diagnostic::{SpanHandler, Handler, Auto, FatalError};
 use parse::attr::ParserAttr;
 use parse::parser::Parser;
@@ -203,7 +203,14 @@ pub fn new_sub_parser_from_file<'a>(sess: &'a ParseSess,
 pub fn filemap_to_parser<'a>(sess: &'a ParseSess,
                              filemap: Rc<FileMap>,
                              cfg: ast::CrateConfig) -> Parser<'a> {
-    tts_to_parser(sess, filemap_to_tts(sess, filemap), cfg)
+    let end_pos = filemap.end_pos;
+    let mut parser = tts_to_parser(sess, filemap_to_tts(sess, filemap), cfg);
+
+    if parser.token == token::Eof && parser.span == codemap::DUMMY_SP {
+        parser.span = codemap::mk_sp(end_pos, end_pos);
+    }
+
+    parser
 }
 
 // must preserve old name for now, because quote! from the *existing*

src/libsyntax/parse/parser.rs

@@ -4824,8 +4824,14 @@ impl<'a> Parser<'a> {
             return Err(self.fatal(&format!("expected item, found `{}`", token_str)));
         }
 
+        let hi = if self.span == codemap::DUMMY_SP {
+            inner_lo
+        } else {
+            self.span.lo
+        };
+
         Ok(ast::Mod {
-            inner: mk_sp(inner_lo, self.span.lo),
+            inner: mk_sp(inner_lo, hi),
             items: items
         })
     }
@@ -4869,8 +4875,7 @@ impl<'a> Parser<'a> {
 
     fn push_mod_path(&mut self, id: Ident, attrs: &[Attribute]) {
         let default_path = self.id_to_interned_str(id);
-        let file_path = match ::attr::first_attr_value_str_by_name(attrs,
+        let file_path = match ::attr::first_attr_value_str_by_name(attrs, "path") {
-                                                                   "path") {
             Some(d) => d,
             None => default_path,
         };
@@ -5003,8 +5008,7 @@ impl<'a> Parser<'a> {
         included_mod_stack.push(path.clone());
         drop(included_mod_stack);
 
-        let mut p0 =
+        let mut p0 = new_sub_parser_from_file(self.sess,
-            new_sub_parser_from_file(self.sess,
                                               self.cfg.clone(),
                                               &path,
                                               owns_directory,