parser: simplify directory ownership semantics

src/librustc/lint/builtin.rs

@@ -204,6 +204,13 @@ declare_lint! {
     "detects extra requirements in impls that were erroneously allowed"
 }
 
+declare_lint! {
+    pub LEGACY_DIRECTORY_OWNERSHIP,
+    Warn,
+    "non-inline, non-`#[path]` modules (e.g. `mod foo;`) were erroneously allowed in some files \
+     not named `mod.rs`"
+}
+
 /// Does nothing as a lint pass, but registers some `Lint`s
 /// which are used by other parts of the compiler.
 #[derive(Copy, Clone)]
@@ -242,7 +249,8 @@ impl LintPass for HardwiredLints {
             LIFETIME_UNDERSCORE,
             SAFE_EXTERN_STATICS,
             PATTERNS_IN_FNS_WITHOUT_BODY,
-            EXTRA_REQUIREMENT_IN_IMPL
+            EXTRA_REQUIREMENT_IN_IMPL,
+            LEGACY_DIRECTORY_OWNERSHIP
         )
     }
 }

src/librustc_lint/lib.rs

@@ -232,6 +232,10 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
             id: LintId::of(EXTRA_REQUIREMENT_IN_IMPL),
             reference: "issue #37166 </~https://github.com/rust-lang/rust/issues/37166>",
         },
+        FutureIncompatibleInfo {
+            id: LintId::of(LEGACY_DIRECTORY_OWNERSHIP),
+            reference: "issue #37872 </~https://github.com/rust-lang/rust/issues/37872>",
+        },
         ]);
 
     // Register renamed and removed lints

src/librustc_passes/ast_validation.rs

@@ -207,6 +207,13 @@ impl<'a> Visitor for AstValidator<'a> {
             ItemKind::Mod(_) => {
                 // Ensure that `path` attributes on modules are recorded as used (c.f. #35584).
                 attr::first_attr_value_str_by_name(&item.attrs, "path");
+                if let Some(attr) =
+                        item.attrs.iter().find(|attr| attr.name() == "warn_directory_ownership") {
+                    let lint = lint::builtin::LEGACY_DIRECTORY_OWNERSHIP;
+                    let msg = "cannot declare a new module at this location";
+                    self.session.add_lint(lint, item.id, item.span, msg.to_string());
+                    attr::mark_used(attr);
+                }
             }
             ItemKind::Union(ref vdata, _) => {
                 if !vdata.is_struct() {

src/libsyntax/ext/base.rs

@@ -18,7 +18,7 @@ use errors::DiagnosticBuilder;
 use ext::expand::{self, Expansion};
 use ext::hygiene::Mark;
 use fold::{self, Folder};
-use parse::{self, parser};
+use parse::{self, parser, DirectoryOwnership};
 use parse::token;
 use ptr::P;
 use symbol::Symbol;
@@ -568,9 +568,7 @@ pub struct ExpansionData {
     pub depth: usize,
     pub backtrace: ExpnId,
     pub module: Rc<ModuleData>,
-
-    // True if non-inline modules without a `#[path]` are forbidden at the root of this expansion.
-    pub no_noninline_mod: bool,
+    pub directory_ownership: DirectoryOwnership,
 }
 
 /// One of these is made during expansion and incrementally updated as we go;
@@ -601,7 +599,7 @@ impl<'a> ExtCtxt<'a> {
                 depth: 0,
                 backtrace: NO_EXPANSION,
                 module: Rc::new(ModuleData { mod_path: Vec::new(), directory: PathBuf::new() }),
-                no_noninline_mod: false,
+                directory_ownership: DirectoryOwnership::Owned,
             },
         }
     }

src/libsyntax/ext/expand.rs

@@ -21,7 +21,7 @@ use ext::base::*;
 use feature_gate::{self, Features};
 use fold;
 use fold::*;
-use parse::{ParseSess, PResult, lexer};
+use parse::{ParseSess, DirectoryOwnership, PResult, lexer};
 use parse::parser::Parser;
 use parse::token;
 use print::pprust;
@@ -727,9 +727,10 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
     }
 
     fn fold_block(&mut self, block: P<Block>) -> P<Block> {
-        let no_noninline_mod = mem::replace(&mut self.cx.current_expansion.no_noninline_mod, true);
+        let old_directory_ownership = self.cx.current_expansion.directory_ownership;
+        self.cx.current_expansion.directory_ownership = DirectoryOwnership::UnownedViaBlock;
         let result = noop_fold_block(block, self);
-        self.cx.current_expansion.no_noninline_mod = no_noninline_mod;
+        self.cx.current_expansion.directory_ownership = old_directory_ownership;
         result
     }
 
@@ -768,7 +769,7 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
                     return noop_fold_item(item, self);
                 }
 
-                let orig_no_noninline_mod = self.cx.current_expansion.no_noninline_mod;
+                let orig_directory_ownership = self.cx.current_expansion.directory_ownership;
                 let mut module = (*self.cx.current_expansion.module).clone();
                 module.mod_path.push(item.ident);
 
@@ -779,23 +780,28 @@ 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.no_noninline_mod = false;
+                        self.cx.current_expansion.directory_ownership = DirectoryOwnership::Owned;
                         module.directory.push(&*path.as_str());
                     } else {
                         module.directory.push(&*item.ident.name.as_str());
                     }
                 } else {
-                    self.cx.current_expansion.no_noninline_mod = false;
-                    module.directory =
+                    let mut path =
                         PathBuf::from(self.cx.parse_sess.codemap().span_to_filename(inner));
-                    module.directory.pop();
+                    let directory_ownership = match path.file_name().unwrap().to_str() {
+                        Some("mod.rs") => DirectoryOwnership::Owned,
+                        _ => DirectoryOwnership::UnownedViaMod(false),
+                    };
+                    path.pop();
+                    module.directory = path;
+                    self.cx.current_expansion.directory_ownership = directory_ownership;
                 }
 
                 let orig_module =
                     mem::replace(&mut self.cx.current_expansion.module, Rc::new(module));
                 let result = noop_fold_item(item, self);
                 self.cx.current_expansion.module = orig_module;
-                self.cx.current_expansion.no_noninline_mod = orig_no_noninline_mod;
+                self.cx.current_expansion.directory_ownership = orig_directory_ownership;
                 return result;
             }
             // Ensure that test functions are accessible from the test harness.

src/libsyntax/ext/source_util.rs

@@ -13,7 +13,7 @@ use syntax_pos::{self, Pos, Span};
 use ext::base::*;
 use ext::base;
 use ext::build::AstBuilder;
-use parse::token;
+use parse::{token, DirectoryOwnership};
 use parse;
 use print::pprust;
 use ptr::P;
@@ -90,7 +90,8 @@ 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 p = parse::new_sub_parser_from_file(cx.parse_sess(), &path, true, None, sp);
+    let directory_ownership = DirectoryOwnership::Owned;
+    let p = parse::new_sub_parser_from_file(cx.parse_sess(), &path, directory_ownership, None, sp);
 
     struct ExpandResult<'a> {
         p: parse::parser::Parser<'a>,

src/libsyntax/ext/tt/macro_rules.rs

@@ -19,7 +19,7 @@ use ext::tt::macro_parser::{MatchedSeq, MatchedNonterminal};
 use ext::tt::macro_parser::{parse, parse_failure_msg};
 use parse::ParseSess;
 use parse::lexer::new_tt_reader;
-use parse::parser::{Parser, Restrictions};
+use parse::parser::Parser;
 use parse::token::{self, NtTT, Token};
 use parse::token::Token::*;
 use print;
@@ -117,11 +117,12 @@ fn generic_extension<'cx>(cx: &'cx ExtCtxt,
                 let trncbr =
                     new_tt_reader(&cx.parse_sess.span_diagnostic, Some(named_matches), rhs);
                 let mut p = Parser::new(cx.parse_sess(), Box::new(trncbr));
-                p.directory = cx.current_expansion.module.directory.clone();
-                p.restrictions = match cx.current_expansion.no_noninline_mod {
-                    true => Restrictions::NO_NONINLINE_MOD,
-                    false => Restrictions::empty(),
-                };
+                let module = &cx.current_expansion.module;
+                p.directory.path = module.directory.clone();
+                p.directory.ownership = cx.current_expansion.directory_ownership;
+                p.root_module_name =
+                    module.mod_path.last().map(|id| (*id.name.as_str()).to_owned());
+
                 p.check_unknown_macro_variable();
                 // Let the context choose how to interpret the result.
                 // Weird, but useful for X-macros.

src/libsyntax/parse/mod.rs

@@ -76,6 +76,19 @@ impl ParseSess {
     }
 }
 
+#[derive(Clone)]
+pub struct Directory {
+    pub path: PathBuf,
+    pub ownership: DirectoryOwnership,
+}
+
+#[derive(Copy, Clone)]
+pub enum DirectoryOwnership {
+    Owned,
+    UnownedViaBlock,
+    UnownedViaMod(bool /* legacy warnings? */),
+}
+
 // a bunch of utility functions of the form parse_<thing>_from_<source>
 // where <thing> includes crate, expr, item, stmt, tts, and one that
 // uses a HOF to parse anything, and <source> includes file and
@@ -152,11 +165,11 @@ pub fn new_parser_from_file<'a>(sess: &'a ParseSess, path: &Path) -> Parser<'a>
 /// On an error, use the given span as the source of the problem.
 pub fn new_sub_parser_from_file<'a>(sess: &'a ParseSess,
                                     path: &Path,
-                                    owns_directory: bool,
+                                    directory_ownership: DirectoryOwnership,
                                     module_name: Option<String>,
                                     sp: Span) -> Parser<'a> {
     let mut p = filemap_to_parser(sess, file_to_filemap(sess, path, Some(sp)));
-    p.owns_directory = owns_directory;
+    p.directory.ownership = directory_ownership;
     p.root_module_name = module_name;
     p
 }