Invalid module location

src/libsyntax/parse/parser.rs

@@ -57,9 +57,11 @@ use tokenstream::{self, Delimited, ThinTokenStream, TokenTree, TokenStream};
 use symbol::{Symbol, keywords};
 use util::ThinVec;
 
+use std::cmp;
 use std::collections::HashSet;
-use std::{cmp, mem, slice};
+use std::mem;
 use std::path::{self, Path, PathBuf};
+use std::slice;
 
 bitflags! {
     flags Restrictions: u8 {
@@ -5363,24 +5365,25 @@ impl<'a> Parser<'a> {
             }
             let mut err = self.diagnostic().struct_span_err(id_sp,
                 "cannot declare a new module at this location");
-            let this_module = match self.directory.path.file_name() {
-                Some(file_name) => file_name.to_str().unwrap().to_owned(),
-                None => self.root_module_name.as_ref().unwrap().clone(),
-            };
-            err.span_note(id_sp,
-                          &format!("maybe move this module `{0}` to its own directory \
-                                    via `{0}{1}mod.rs`",
-                                   this_module,
-                                   path::MAIN_SEPARATOR));
+            if id_sp != syntax_pos::DUMMY_SP {
+                let src_path = PathBuf::from(self.sess.codemap().span_to_filename(id_sp));
+                if let Some(stem) = src_path.file_stem() {
+                    let mut dest_path = src_path.clone();
+                    dest_path.set_file_name(stem);
+                    dest_path.push("mod.rs");
+                    err.span_note(id_sp,
+                                  &format!("maybe move this module `{}` to its own \
+                                            directory via `{}`", src_path.to_string_lossy(),
+                                           dest_path.to_string_lossy()));
+                }
+            }
             if paths.path_exists {
                 err.span_note(id_sp,
                               &format!("... or maybe `use` the module `{}` instead \
                                         of possibly redeclaring it",
                                        paths.name));
-                Err(err)
-            } else {
-                Err(err)
             }
+            Err(err)
         } else {
             paths.result.map_err(|err| self.span_fatal_err(id_sp, err))
         }

src/test/ui/invalid-module-declaration/auxiliary/foo/bar.rs

@@ -0,0 +1,11 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub mod baz;

src/test/ui/invalid-module-declaration/auxiliary/foo/mod.rs

@@ -0,0 +1,11 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub mod bar;

src/test/ui/invalid-module-declaration/invalid-module-declaration.rs

@@ -0,0 +1,20 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-tidy-linelength
+
+// error-pattern: cannot declare a new module at this location
+// error-pattern: maybe move this module
+
+mod auxiliary {
+    mod foo;
+}
+
+fn main() {}

src/test/ui/invalid-module-declaration/invalid-module-declaration.stderr

@@ -0,0 +1,14 @@
+error: cannot declare a new module at this location
+  --> $DIR/auxiliary/foo/bar.rs:11:9
+   |
+11 | pub mod baz;
+   |         ^^^
+   |
+note: maybe move this module `$DIR/auxiliary/foo/bar.rs` to its own directory via `$DIR/auxiliary/foo/bar/mod.rs`
+  --> $DIR/auxiliary/foo/bar.rs:11:9
+   |
+11 | pub mod baz;
+   |         ^^^
+
+error: aborting due to previous error
+