Auto merge of #46531 - cramertj:no-mo-modrs, r=nikomatsakis

Implement non-mod.rs mod statements

Fixes #45385, cc #44660

This will fail tidy right now because it doesn't recognize my UI tests as feature-gate tests. However, I'm not sure if compile-fail will work out either because compile-fail usually requires there to be error patterns in the top-level file, which isn't possible with this feature. What's the recommended way to handle this?

src/libsyntax/ext/base.rs

@@ -688,7 +688,7 @@ impl<'a> ExtCtxt<'a> {
                 mark: Mark::root(),
                 depth: 0,
                 module: Rc::new(ModuleData { mod_path: Vec::new(), directory: PathBuf::new() }),
-                directory_ownership: DirectoryOwnership::Owned,
+                directory_ownership: DirectoryOwnership::Owned { relative: None },
             },
             expansions: HashMap::new(),
         }

src/libsyntax/ext/expand.rs

@@ -974,16 +974,20 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
 
                 if inline_module {
                     if let Some(path) = attr::first_attr_value_str_by_name(&item.attrs, "path") {
-                        self.cx.current_expansion.directory_ownership = DirectoryOwnership::Owned;
+                        self.cx.current_expansion.directory_ownership =
+                            DirectoryOwnership::Owned { relative: None };
                         module.directory.push(&*path.as_str());
                     } else {
                         module.directory.push(&*item.ident.name.as_str());
                     }
                 } else {
                     let mut path = self.cx.parse_sess.codemap().span_to_unmapped_path(inner);
                     let directory_ownership = match path.file_name().unwrap().to_str() {
-                        Some("mod.rs") => DirectoryOwnership::Owned,
-                        _ => DirectoryOwnership::UnownedViaMod(false),
+                        Some("mod.rs") => DirectoryOwnership::Owned { relative: None },
+                        Some(_) => DirectoryOwnership::Owned {
+                            relative: Some(item.ident),
+                        },
+                        None => DirectoryOwnership::UnownedViaMod(false),
                     };
                     path.pop();
                     module.directory = path;

src/libsyntax/ext/source_util.rs

@@ -100,7 +100,7 @@ pub fn expand_include<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[tokenstream::T
     };
     // The file will be added to the code map by the parser
     let path = res_rel_file(cx, sp, Path::new(&file));
-    let directory_ownership = DirectoryOwnership::Owned;
+    let directory_ownership = DirectoryOwnership::Owned { relative: None };
     let p = parse::new_sub_parser_from_file(cx.parse_sess(), &path, directory_ownership, None, sp);
 
     struct ExpandResult<'a> {

src/libsyntax/feature_gate.rs

@@ -35,7 +35,7 @@ use visit::{self, FnKind, Visitor};
 use parse::ParseSess;
 use symbol::{keywords, Symbol};
 
-use std::env;
+use std::{env, path};
 
 macro_rules! set {
     (proc_macro) => {{
@@ -430,6 +430,9 @@ declare_features! (
 
     // generic associated types (RFC 1598)
     (active, generic_associated_types, "1.23.0", Some(44265)),
+
+    // `foo.rs` as an alternative to `foo/mod.rs`
+    (active, non_modrs_mods, "1.24.0", Some(44660)),
 );
 
 declare_features! (
@@ -1297,6 +1300,31 @@ fn contains_novel_literal(item: &ast::MetaItem) -> bool {
     }
 }
 
+impl<'a> PostExpansionVisitor<'a> {
+    fn whole_crate_feature_gates(&mut self) {
+        for &(ident, span) in &*self.context.parse_sess.non_modrs_mods.borrow() {
+            if !span.allows_unstable() {
+                let cx = &self.context;
+                let level = GateStrength::Hard;
+                let has_feature = cx.features.non_modrs_mods;
+                let name = "non_modrs_mods";
+                debug!("gate_feature(feature = {:?}, span = {:?}); has? {}",
+                        name, span, has_feature);
+
+                if !has_feature && !span.allows_unstable() {
+                    leveled_feature_err(
+                        cx.parse_sess, name, span, GateIssue::Language,
+                        "mod statements in non-mod.rs files are unstable", level
+                    )
+                    .help(&format!("on stable builds, rename this file to {}{}mod.rs",
+                                   ident, path::MAIN_SEPARATOR))
+                    .emit();
+                }
+            }
+        }
+    }
+}
+
 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
     fn visit_attribute(&mut self, attr: &ast::Attribute) {
         if !attr.span.allows_unstable() {
@@ -1843,7 +1871,9 @@ pub fn check_crate(krate: &ast::Crate,
         parse_sess: sess,
         plugin_attributes,
     };
-    visit::walk_crate(&mut PostExpansionVisitor { context: &ctx }, krate);
+    let visitor = &mut PostExpansionVisitor { context: &ctx };
+    visitor.whole_crate_feature_gates();
+    visit::walk_crate(visitor, krate);
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, Hash)]

src/libsyntax/parse/lexer/mod.rs

@@ -1727,6 +1727,7 @@ mod tests {
             included_mod_stack: RefCell::new(Vec::new()),
             code_map: cm,
             missing_fragment_specifiers: RefCell::new(HashSet::new()),
+            non_modrs_mods: RefCell::new(vec![]),
         }
     }
 

src/libsyntax/parse/mod.rs

@@ -47,6 +47,9 @@ pub struct ParseSess {
     pub unstable_features: UnstableFeatures,
     pub config: CrateConfig,
     pub missing_fragment_specifiers: RefCell<HashSet<Span>>,
+    // Spans where a `mod foo;` statement was included in a non-mod.rs file.
+    // These are used to issue errors if the non_modrs_mods feature is not enabled.
+    pub non_modrs_mods: RefCell<Vec<(ast::Ident, Span)>>,
     /// Used to determine and report recursive mod inclusions
     included_mod_stack: RefCell<Vec<PathBuf>>,
     code_map: Rc<CodeMap>,
@@ -70,6 +73,7 @@ impl ParseSess {
             missing_fragment_specifiers: RefCell::new(HashSet::new()),
             included_mod_stack: RefCell::new(vec![]),
             code_map,
+            non_modrs_mods: RefCell::new(vec![]),
         }
     }
 
@@ -86,7 +90,10 @@ pub struct Directory {
 
 #[derive(Copy, Clone)]
 pub enum DirectoryOwnership {
-    Owned,
+    Owned {
+        // None if `mod.rs`, `Some("foo")` if we're in `foo.rs`
+        relative: Option<ast::Ident>,
+    },
     UnownedViaBlock,
     UnownedViaMod(bool /* legacy warnings? */),
 }

src/libsyntax/parse/parser.rs

@@ -507,7 +507,10 @@ impl<'a> Parser<'a> {
             restrictions: Restrictions::empty(),
             obsolete_set: HashSet::new(),
             recurse_into_file_modules,
-            directory: Directory { path: PathBuf::new(), ownership: DirectoryOwnership::Owned },
+            directory: Directory {
+                path: PathBuf::new(),
+                ownership: DirectoryOwnership::Owned { relative: None }
+            },
             root_module_name: None,
             expected_tokens: Vec::new(),
             token_cursor: TokenCursor {
@@ -5676,7 +5679,7 @@ impl<'a> Parser<'a> {
     fn push_directory(&mut self, id: Ident, attrs: &[Attribute]) {
         if let Some(path) = attr::first_attr_value_str_by_name(attrs, "path") {
             self.directory.path.push(&path.as_str());
-            self.directory.ownership = DirectoryOwnership::Owned;
+            self.directory.ownership = DirectoryOwnership::Owned { relative: None };
         } else {
             self.directory.path.push(&id.name.as_str());
         }
@@ -5687,10 +5690,28 @@ impl<'a> Parser<'a> {
     }
 
     /// Returns either a path to a module, or .
-    pub fn default_submod_path(id: ast::Ident, dir_path: &Path, codemap: &CodeMap) -> ModulePath {
+    pub fn default_submod_path(
+        id: ast::Ident,
+        relative: Option<ast::Ident>,
+        dir_path: &Path,
+        codemap: &CodeMap) -> ModulePath
+    {
+        // If we're in a foo.rs file instead of a mod.rs file,
+        // we need to look for submodules in
+        // `./foo/<id>.rs` and `./foo/<id>/mod.rs` rather than
+        // `./<id>.rs` and `./<id>/mod.rs`.
+        let relative_prefix_string;
+        let relative_prefix = if let Some(ident) = relative {
+            relative_prefix_string = format!("{}{}", ident.name.as_str(), path::MAIN_SEPARATOR);
+            &relative_prefix_string
+        } else {
+            ""
+        };
+
         let mod_name = id.to_string();
-        let default_path_str = format!("{}.rs", mod_name);
-        let secondary_path_str = format!("{}{}mod.rs", mod_name, path::MAIN_SEPARATOR);
+        let default_path_str = format!("{}{}.rs", relative_prefix, mod_name);
+        let secondary_path_str = format!("{}{}{}mod.rs",
+                                         relative_prefix, mod_name, path::MAIN_SEPARATOR);
         let default_path = dir_path.join(&default_path_str);
         let secondary_path = dir_path.join(&secondary_path_str);
         let default_exists = codemap.file_exists(&default_path);
@@ -5699,12 +5720,16 @@ impl<'a> Parser<'a> {
         let result = match (default_exists, secondary_exists) {
             (true, false) => Ok(ModulePathSuccess {
                 path: default_path,
-                directory_ownership: DirectoryOwnership::UnownedViaMod(false),
+                directory_ownership: DirectoryOwnership::Owned {
+                    relative: Some(id),
+                },
                 warn: false,
             }),
             (false, true) => Ok(ModulePathSuccess {
                 path: secondary_path,
-                directory_ownership: DirectoryOwnership::Owned,
+                directory_ownership: DirectoryOwnership::Owned {
+                    relative: None,
+                },
                 warn: false,
             }),
             (false, false) => Err(Error::FileNotFoundForModule {
@@ -5735,55 +5760,78 @@ impl<'a> Parser<'a> {
         if let Some(path) = Parser::submod_path_from_attr(outer_attrs, &self.directory.path) {
             return Ok(ModulePathSuccess {
                 directory_ownership: match path.file_name().and_then(|s| s.to_str()) {
-                    Some("mod.rs") => DirectoryOwnership::Owned,
+                    Some("mod.rs") => DirectoryOwnership::Owned { relative: None },
+                    Some(_) => {
+                        DirectoryOwnership::Owned { relative: Some(id) }
+                    }
                     _ => DirectoryOwnership::UnownedViaMod(true),
                 },
                 path,
                 warn: false,
             });
         }
 
-        let paths = Parser::default_submod_path(id, &self.directory.path, self.sess.codemap());
+        let relative = match self.directory.ownership {
+            DirectoryOwnership::Owned { relative } => {
+                // Push the usage onto the list of non-mod.rs mod uses.
+                // This is used later for feature-gate error reporting.
+                if let Some(cur_file_ident) = relative {
+                    self.sess
+                        .non_modrs_mods.borrow_mut()
+                        .push((cur_file_ident, id_sp));
+                }
+                relative
+            },
+            DirectoryOwnership::UnownedViaBlock |
+            DirectoryOwnership::UnownedViaMod(_) => None,
+        };
+        let paths = Parser::default_submod_path(
+                        id, relative, &self.directory.path, self.sess.codemap());
 
-        if let DirectoryOwnership::UnownedViaBlock = self.directory.ownership {
-            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);
-            }
-            Err(err)
-        } else if let DirectoryOwnership::UnownedViaMod(warn) = self.directory.ownership {
-            if warn {
-                if let Ok(result) = paths.result {
-                    return Ok(ModulePathSuccess { warn: true, ..result });
+        match self.directory.ownership {
+            DirectoryOwnership::Owned { .. } => {
+                paths.result.map_err(|err| self.span_fatal_err(id_sp, err))
+            },
+            DirectoryOwnership::UnownedViaBlock => {
+                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);
                 }
+                Err(err)
             }
-            let mut err = self.diagnostic().struct_span_err(id_sp,
-                "cannot declare a new module at this location");
-            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");
+            DirectoryOwnership::UnownedViaMod(warn) => {
+                if warn {
+                    if let Ok(result) = paths.result {
+                        return Ok(ModulePathSuccess { warn: true, ..result });
+                    }
+                }
+                let mut err = self.diagnostic().struct_span_err(id_sp,
+                    "cannot declare a new module at this location");
+                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!("maybe move this module `{}` to its own \
-                                            directory via `{}`", src_path.to_string_lossy(),
-                                           dest_path.to_string_lossy()));
+                                  &format!("... or maybe `use` the module `{}` instead \
+                                            of possibly redeclaring it",
+                                           paths.name));
                 }
+                Err(err)
             }
-            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 {
-            paths.result.map_err(|err| self.span_fatal_err(id_sp, err))
         }
     }
 

src/test/compile-fail/directory_ownership/backcompat-warnings.rs

@@ -8,8 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern: cannot declare a new module at this location
-// error-pattern: will become a hard error
+// error-pattern: mod statements in non-mod.rs files are unstable
 
 #[path="mod_file_not_owning_aux3.rs"]
 mod foo;

src/test/compile-fail/directory_ownership/foo/mod_file_not_owning/aux2.rs

@@ -0,0 +1,9 @@
+// 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.

src/test/compile-fail/directory_ownership/foo/mod_file_not_owning_aux2.rs

@@ -0,0 +1,9 @@
+// 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.

src/test/compile-fail/directory_ownership/mod_file_not_owning.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern: cannot declare a new module at this location
+// error-pattern: mod statements in non-mod.rs files are unstable
 
 mod mod_file_not_owning_aux1;
 

src/test/compile-fail/directory_ownership/mod_file_not_owning_aux1/mod_file_not_owning_aux2.rs

@@ -0,0 +1,9 @@
+// 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.

src/test/compile-fail/directory_ownership/unowned_mod_with_path.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern: cannot declare a new module at this location
+// error-pattern: mod statements in non-mod.rs files are unstable
 
 // This is not a directory owner since the file name is not "mod.rs".
 #[path = "mod_file_not_owning_aux1.rs"]