libsyntax: Restrict where non-inline modules can appear (fixes #29765)

src/librustc_back/target/mod.rs

@@ -65,12 +65,13 @@ mod windows_msvc_base;
 
 macro_rules! supported_targets {
     ( $(($triple:expr, $module:ident)),+ ) => (
+        $(mod $module;)*
+
         /// List of supported targets
         pub const TARGETS: &'static [&'static str] = &[$($triple),*];
 
         // this would use a match if stringify! were allowed in pattern position
         fn load_specific(target: &str) -> Option<Target> {
-            $(mod $module;)*
             let target = target.replace("-", "_");
             if false { }
             $(

src/libsyntax/parse/parser.rs

@@ -73,6 +73,7 @@ bitflags! {
     flags Restrictions: u8 {
         const RESTRICTION_STMT_EXPR         = 1 << 0,
         const RESTRICTION_NO_STRUCT_LITERAL = 1 << 1,
+        const NO_NONINLINE_MOD  = 1 << 2,
     }
 }
 
@@ -3208,8 +3209,8 @@ impl<'a> Parser<'a> {
     /// Evaluate the closure with restrictions in place.
     ///
     /// After the closure is evaluated, restrictions are reset.
-    pub fn with_res<F>(&mut self, r: Restrictions, f: F) -> PResult<'a, P<Expr>>
-        where F: FnOnce(&mut Self) -> PResult<'a,  P<Expr>>
+    pub fn with_res<F, T>(&mut self, r: Restrictions, f: F) -> T
+        where F: FnOnce(&mut Self) -> T
     {
         let old = self.restrictions;
         self.restrictions = r;
@@ -3767,7 +3768,9 @@ impl<'a> Parser<'a> {
             }
         } else {
             // FIXME: Bad copy of attrs
-            match try!(self.parse_item_(attrs.clone(), false, true)) {
+            let restrictions = self.restrictions | Restrictions::NO_NONINLINE_MOD;
+            match try!(self.with_res(restrictions,
+                                     |this| this.parse_item_(attrs.clone(), false, true))) {
                 Some(i) => {
                     let hi = i.span.hi;
                     let decl = P(spanned(lo, hi, DeclKind::Item(i)));
@@ -5096,11 +5099,8 @@ impl<'a> Parser<'a> {
             self.push_mod_path(id, outer_attrs);
             try!(self.expect(&token::OpenDelim(token::Brace)));
             let mod_inner_lo = self.span.lo;
-            let old_owns_directory = self.owns_directory;
-            self.owns_directory = true;
             let attrs = try!(self.parse_inner_attributes());
             let m = try!(self.parse_mod_items(&token::CloseDelim(token::Brace), mod_inner_lo));
-            self.owns_directory = old_owns_directory;
             self.pop_mod_path();
             Ok((id, ItemKind::Mod(m), Some(attrs)))
         }
@@ -5177,7 +5177,17 @@ impl<'a> Parser<'a> {
 
         let paths = Parser::default_submod_path(id, &dir_path, self.sess.codemap());
 
-        if !self.owns_directory {
+        if self.restrictions.contains(Restrictions::NO_NONINLINE_MOD) {
+            let msg =
+                "Cannot declare a non-inline module inside a block unless it has a path attribute";
+            let mut err = self.diagnostic().struct_span_err(id_sp, msg);
+            if paths.path_exists {
+                let msg = format!("Maybe `use` the module `{}` instead of redeclaring it",
+                                  paths.name);
+                err.span_note(id_sp, &msg);
+            }
+            return Err(err);
+        } else if !self.owns_directory {
             let mut err = self.diagnostic().struct_span_err(id_sp,
                 "cannot declare a new module at this location");
             let this_module = match self.mod_path_stack.last() {

src/test/compile-fail/non-inline-mod-restriction.rs

@@ -0,0 +1,15 @@
+// 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.
+
+// Test that non-inline modules are not allowed inside blocks.
+
+fn main() {
+    mod foo; //~ ERROR Cannot declare a non-inline module inside a block
+}