rust-lang · bors · Sep 10, 2020 · Aug 23, 2020
diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
@@ -2289,22 +2289,28 @@ impl FnRetTy {
 /// Module declaration.
 ///
 /// E.g., `mod foo;` or `mod foo { .. }`.
-#[derive(Clone, Encodable, Decodable, Debug, Default)]
+#[derive(Clone, Encodable, Decodable, Debug)]
 pub struct Mod {
     /// A span from the first token past `{` to the last token until `}`.
     /// For `mod foo;`, the inner span ranges from the first token
     /// to the last token in the external file.
     pub inner: Span,
+    /// `unsafe` keyword accepted syntactically for macro DSLs, but not
+    /// semantically by Rust.
+    pub unsafety: Unsafe,
     pub items: Vec<P<Item>>,
     /// `true` for `mod foo { .. }`; `false` for `mod foo;`.
     pub inline: bool,
 }
 
 /// Foreign module declaration.
 ///
-/// E.g., `extern { .. }` or `extern C { .. }`.
+/// E.g., `extern { .. }` or `extern "C" { .. }`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct ForeignMod {
+    /// `unsafe` keyword accepted syntactically for macro DSLs, but not
+    /// semantically by Rust.
+    pub unsafety: Unsafe,
     pub abi: Option<StrLit>,
     pub items: Vec<P<ForeignItem>>,
 }

diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
@@ -490,7 +490,7 @@ pub fn noop_visit_ty<T: MutVisitor>(ty: &mut P<Ty>, vis: &mut T) {
 }
 
 pub fn noop_visit_foreign_mod<T: MutVisitor>(foreign_mod: &mut ForeignMod, vis: &mut T) {
-    let ForeignMod { abi: _, items } = foreign_mod;
+    let ForeignMod { unsafety: _, abi: _, items } = foreign_mod;
     items.flat_map_in_place(|item| vis.flat_map_foreign_item(item));
 }
 
@@ -970,7 +970,8 @@ pub fn noop_visit_fn_header<T: MutVisitor>(header: &mut FnHeader, vis: &mut T) {
     vis.visit_asyncness(asyncness);
 }
 
-pub fn noop_visit_mod<T: MutVisitor>(Mod { inner, items, inline: _ }: &mut Mod, vis: &mut T) {
+pub fn noop_visit_mod<T: MutVisitor>(module: &mut Mod, vis: &mut T) {
+    let Mod { inner, unsafety: _, items, inline: _ } = module;
     vis.visit_span(inner);
     items.flat_map_in_place(|item| vis.flat_map_item(item));
 }
@@ -990,7 +991,7 @@ pub fn noop_visit_crate<T: MutVisitor>(krate: &mut Crate, vis: &mut T) {
 
         let len = items.len();
         if len == 0 {
-            let module = Mod { inner: span, items: vec![], inline: true };
+            let module = Mod { inner: span, unsafety: Unsafe::No, items: vec![], inline: true };
             Crate { module, attrs: vec![], span, proc_macros }
         } else if len == 1 {
             let Item { attrs, span, kind, .. } = items.into_iter().next().unwrap().into_inner();

diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -990,12 +990,15 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     self.error_item_without_body(item.span, "function", msg, " { <body> }");
                 }
             }
-            ItemKind::ForeignMod(_) => {
+            ItemKind::ForeignMod(ForeignMod { unsafety, .. }) => {
                 let old_item = mem::replace(&mut self.extern_mod, Some(item));
                 self.invalid_visibility(
                     &item.vis,
                     Some("place qualifiers on individual foreign items instead"),
                 );
+                if let Unsafe::Yes(span) = unsafety {
+                    self.err_handler().span_err(span, "extern block cannot be declared unsafe");
+                }
                 visit::walk_item(self, item);
                 self.extern_mod = old_item;
                 return; // Avoid visiting again.
@@ -1029,7 +1032,10 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 walk_list!(self, visit_attribute, &item.attrs);
                 return;
             }
-            ItemKind::Mod(Mod { inline, .. }) => {
+            ItemKind::Mod(Mod { inline, unsafety, .. }) => {
+                if let Unsafe::Yes(span) = unsafety {
+                    self.err_handler().span_err(span, "module cannot be declared unsafe");
+                }
                 // Ensure that `path` attributes on modules are recorded as used (cf. issue #35584).
                 if !inline && !self.session.contains_name(&item.attrs, sym::path) {
                     self.check_mod_file_item_asciionly(item.ident);

diff --git a/compiler/rustc_ast_pretty/src/pprust.rs b/compiler/rustc_ast_pretty/src/pprust.rs
@@ -1139,7 +1139,11 @@ impl<'a> State<'a> {
                 self.print_fn_full(sig, item.ident, gen, &item.vis, def, body, &item.attrs);
             }
             ast::ItemKind::Mod(ref _mod) => {
-                self.head(visibility_qualified(&item.vis, "mod"));
+                self.head(to_string(|s| {
+                    s.print_visibility(&item.vis);
+                    s.print_unsafety(_mod.unsafety);
+                    s.word("mod");
+                }));
                 self.print_ident(item.ident);
 
                 if _mod.inline || self.is_expanded {
@@ -1154,7 +1158,10 @@ impl<'a> State<'a> {
                 }
             }
             ast::ItemKind::ForeignMod(ref nmod) => {
-                self.head("extern");
+                self.head(to_string(|s| {
+                    s.print_unsafety(nmod.unsafety);
+                    s.word("extern");
+                }));
                 if let Some(abi) = nmod.abi {
                     self.print_literal(&abi.as_lit());
                     self.nbsp();

diff --git a/compiler/rustc_expand/src/config.rs b/compiler/rustc_expand/src/config.rs
@@ -399,7 +399,7 @@ impl<'a> StripUnconfigured<'a> {
     }
 
     pub fn configure_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
-        let ast::ForeignMod { abi: _, items } = foreign_mod;
+        let ast::ForeignMod { unsafety: _, abi: _, items } = foreign_mod;
         items.flat_map_in_place(|item| self.configure(item));
     }
 

diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
@@ -13,7 +13,7 @@ use rustc_ast::token;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::visit::{self, AssocCtxt, Visitor};
 use rustc_ast::{self as ast, AttrItem, Block, LitKind, NodeId, PatKind, Path};
-use rustc_ast::{ItemKind, MacArgs, MacCallStmt, MacStmtStyle, StmtKind};
+use rustc_ast::{ItemKind, MacArgs, MacCallStmt, MacStmtStyle, StmtKind, Unsafe};
 use rustc_ast_pretty::pprust;
 use rustc_attr::{self as attr, is_builtin_attr, HasAttrs};
 use rustc_data_structures::map_in_place::MapInPlace;
@@ -370,11 +370,21 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             None => {
                 // Resolution failed so we return an empty expansion
                 krate.attrs = vec![];
-                krate.module = ast::Mod { inner: orig_mod_span, items: vec![], inline: true };
+                krate.module = ast::Mod {
+                    inner: orig_mod_span,
+                    unsafety: Unsafe::No,
+                    items: vec![],
+                    inline: true,
+                };
             }
             Some(ast::Item { span, kind, .. }) => {
                 krate.attrs = vec![];
-                krate.module = ast::Mod { inner: orig_mod_span, items: vec![], inline: true };
+                krate.module = ast::Mod {
+                    inner: orig_mod_span,
+                    unsafety: Unsafe::No,
+                    items: vec![],
+                    inline: true,
+                };
                 self.cx.span_err(
                     span,
                     &format!(
@@ -1441,8 +1451,15 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
                     push_directory(&self.cx.sess, ident, &item.attrs, dir)
                 } else {
                     // We have an outline `mod foo;` so we need to parse the file.
-                    let (new_mod, dir) =
-                        parse_external_mod(&self.cx.sess, ident, span, dir, &mut attrs, pushed);
+                    let (new_mod, dir) = parse_external_mod(
+                        &self.cx.sess,
+                        ident,
+                        span,
+                        old_mod.unsafety,
+                        dir,
+                        &mut attrs,
+                        pushed,
+                    );
 
                     let krate = ast::Crate {
                         span: new_mod.inner,

diff --git a/compiler/rustc_expand/src/module.rs b/compiler/rustc_expand/src/module.rs
@@ -1,4 +1,4 @@
-use rustc_ast::{token, Attribute, Mod};
+use rustc_ast::{token, Attribute, Mod, Unsafe};
 use rustc_errors::{struct_span_err, PResult};
 use rustc_parse::new_parser_from_file;
 use rustc_session::parse::ParseSess;
@@ -42,6 +42,7 @@ crate fn parse_external_mod(
     sess: &Session,
     id: Ident,
     span: Span, // The span to blame on errors.
+    unsafety: Unsafe,
     Directory { mut ownership, path }: Directory,
     attrs: &mut Vec<Attribute>,
     pop_mod_stack: &mut bool,
@@ -60,13 +61,16 @@ crate fn parse_external_mod(
         drop(included_mod_stack);
 
         // Actually parse the external file as a module.
-        let mut module =
-            new_parser_from_file(&sess.parse_sess, &mp.path, Some(span)).parse_mod(&token::Eof)?;
+        let mut parser = new_parser_from_file(&sess.parse_sess, &mp.path, Some(span));
+        let mut module = parser.parse_mod(&token::Eof, unsafety)?;
         module.0.inline = false;
         module
     };
     // (1) ...instead, we return a dummy module.
-    let (module, mut new_attrs) = result.map_err(|mut err| err.emit()).unwrap_or_default();
+    let (module, mut new_attrs) = result.map_err(|mut err| err.emit()).unwrap_or_else(|_| {
+        let module = Mod { inner: Span::default(), unsafety, items: Vec::new(), inline: false };
+        (module, Vec::new())
+    });
     attrs.append(&mut new_attrs);
 
     // Extract the directory path for submodules of `module`.

diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
@@ -28,35 +28,46 @@ impl<'a> Parser<'a> {
     /// Parses a source module as a crate. This is the main entry point for the parser.
     pub fn parse_crate_mod(&mut self) -> PResult<'a, ast::Crate> {
         let lo = self.token.span;
-        let (module, attrs) = self.parse_mod(&token::Eof)?;
+        let (module, attrs) = self.parse_mod(&token::Eof, Unsafe::No)?;
         let span = lo.to(self.token.span);
         let proc_macros = Vec::new(); // Filled in by `proc_macro_harness::inject()`.
         Ok(ast::Crate { attrs, module, span, proc_macros })
     }
 
     /// Parses a `mod <foo> { ... }` or `mod <foo>;` item.
     fn parse_item_mod(&mut self, attrs: &mut Vec<Attribute>) -> PResult<'a, ItemInfo> {
+        let unsafety = self.parse_unsafety();
+        self.expect_keyword(kw::Mod)?;
         let id = self.parse_ident()?;
         let (module, mut inner_attrs) = if self.eat(&token::Semi) {
-            Default::default()
+            (Mod { inner: Span::default(), unsafety, items: Vec::new(), inline: false }, Vec::new())
         } else {
             self.expect(&token::OpenDelim(token::Brace))?;
-            self.parse_mod(&token::CloseDelim(token::Brace))?
+            self.parse_mod(&token::CloseDelim(token::Brace), unsafety)?
         };
         attrs.append(&mut inner_attrs);
         Ok((id, ItemKind::Mod(module)))
     }
 
     /// Parses the contents of a module (inner attributes followed by module items).
-    pub fn parse_mod(&mut self, term: &TokenKind) -> PResult<'a, (Mod, Vec<Attribute>)> {
+    pub fn parse_mod(
+        &mut self,
+        term: &TokenKind,
+        unsafety: Unsafe,
+    ) -> PResult<'a, (Mod, Vec<Attribute>)> {
         let lo = self.token.span;
         let attrs = self.parse_inner_attributes()?;
-        let module = self.parse_mod_items(term, lo)?;
+        let module = self.parse_mod_items(term, lo, unsafety)?;
         Ok((module, attrs))
     }
 
     /// Given a termination token, parses all of the items in a module.
-    fn parse_mod_items(&mut self, term: &TokenKind, inner_lo: Span) -> PResult<'a, Mod> {
+    fn parse_mod_items(
+        &mut self,
+        term: &TokenKind,
+        inner_lo: Span,
+        unsafety: Unsafe,
+    ) -> PResult<'a, Mod> {
         let mut items = vec![];
         while let Some(item) = self.parse_item()? {
             items.push(item);
@@ -75,7 +86,7 @@ impl<'a> Parser<'a> {
 
         let hi = if self.token.span.is_dummy() { inner_lo } else { self.prev_token.span };
 
-        Ok(Mod { inner: inner_lo.to(hi), items, inline: true })
+        Ok(Mod { inner: inner_lo.to(hi), unsafety, items, inline: true })
     }
 }
 
@@ -235,8 +246,13 @@ impl<'a> Parser<'a> {
                 self.parse_item_extern_crate()?
             } else {
                 // EXTERN BLOCK
-                self.parse_item_foreign_mod(attrs)?
+                self.parse_item_foreign_mod(attrs, Unsafe::No)?
             }
+        } else if self.is_unsafe_foreign_mod() {
+            // EXTERN BLOCK
+            let unsafety = self.parse_unsafety();
+            self.expect_keyword(kw::Extern)?;
+            self.parse_item_foreign_mod(attrs, unsafety)?
         } else if self.is_static_global() {
             // STATIC ITEM
             self.bump(); // `static`
@@ -256,7 +272,9 @@ impl<'a> Parser<'a> {
         {
             // IMPL ITEM
             self.parse_item_impl(attrs, def())?
-        } else if self.eat_keyword(kw::Mod) {
+        } else if self.check_keyword(kw::Mod)
+            || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Mod])
+        {
             // MODULE ITEM
             self.parse_item_mod(attrs)?
         } else if self.eat_keyword(kw::Type) {
@@ -893,10 +911,14 @@ impl<'a> Parser<'a> {
     /// extern "C" {}
     /// extern {}
     /// ```
-    fn parse_item_foreign_mod(&mut self, attrs: &mut Vec<Attribute>) -> PResult<'a, ItemInfo> {
+    fn parse_item_foreign_mod(
+        &mut self,
+        attrs: &mut Vec<Attribute>,
+        unsafety: Unsafe,
+    ) -> PResult<'a, ItemInfo> {
         let abi = self.parse_abi(); // ABI?
         let items = self.parse_item_list(attrs, |p| p.parse_foreign_item())?;
-        let module = ast::ForeignMod { abi, items };
+        let module = ast::ForeignMod { unsafety, abi, items };
         Ok((Ident::invalid(), ItemKind::ForeignMod(module)))
     }
 
@@ -938,6 +960,15 @@ impl<'a> Parser<'a> {
             .emit();
     }
 
+    fn is_unsafe_foreign_mod(&self) -> bool {
+        self.token.is_keyword(kw::Unsafe)
+            && self.is_keyword_ahead(1, &[kw::Extern])
+            && self.look_ahead(
+                2 + self.look_ahead(2, |t| t.can_begin_literal_maybe_minus() as usize),
+                |t| t.kind == token::OpenDelim(token::Brace),
+            )
+    }
+
     fn is_static_global(&mut self) -> bool {
         if self.check_keyword(kw::Static) {
             // Check if this could be a closure.
@@ -1552,10 +1583,14 @@ impl<'a> Parser<'a> {
             // `$qual fn` or `$qual $qual`:
             || QUALS.iter().any(|&kw| self.check_keyword(kw))
                 && self.look_ahead(1, |t| {
-                    // ...qualified and then `fn`, e.g. `const fn`.
+                    // `$qual fn`, e.g. `const fn` or `async fn`.
                     t.is_keyword(kw::Fn)
-                    // Two qualifiers. This is enough. Due `async` we need to check that it's reserved.
-                    || t.is_non_raw_ident_where(|i| QUALS.contains(&i.name) && i.is_reserved())
+                    // Two qualifiers `$qual $qual` is enough, e.g. `async unsafe`.
+                    || t.is_non_raw_ident_where(|i| QUALS.contains(&i.name)
+                        // Rule out 2015 `const async: T = val`.
+                        && i.is_reserved()
+                        // Rule out unsafe extern block.
+                        && !self.is_unsafe_foreign_mod())
                 })
             // `extern ABI fn`
             || self.check_keyword(kw::Extern)
@@ -1567,9 +1602,9 @@ impl<'a> Parser<'a> {
     /// up to and including the `fn` keyword. The formal grammar is:
     ///
     /// ```
-    /// Extern = "extern" StringLit ;
+    /// Extern = "extern" StringLit? ;
     /// FnQual = "const"? "async"? "unsafe"? Extern? ;
-    /// FnFrontMatter = FnQual? "fn" ;
+    /// FnFrontMatter = FnQual "fn" ;
     /// ```
     pub(super) fn parse_fn_front_matter(&mut self) -> PResult<'a, FnHeader> {
         let constness = self.parse_constness();

diff --git a/src/test/ui/ast-json/ast-json-noexpand-output.stdout b/src/test/ui/ast-json/ast-json-noexpand-output.stdout
@@ -1 +1 @@
-{"module":{"inner":{"lo":0,"hi":0},"items":[{"attrs":[],"id":0,"span":{"lo":0,"hi":0},"vis":{"node":"Inherited","span":{"lo":0,"hi":0}},"ident":{"name":"core","span":{"lo":0,"hi":0}},"kind":{"variant":"ExternCrate","fields":[null]},"tokens":null}],"inline":true},"attrs":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"crate_type","span":{"lo":0,"hi":0}},"id":0,"args":null}]},"args":{"variant":"Eq","fields":[{"lo":0,"hi":0},{"0":[[{"variant":"Token","fields":[{"kind":{"variant":"Literal","fields":[{"kind":"Str","symbol":"lib","suffix":null}]},"span":{"lo":0,"hi":0}}]},"Alone"]]}]}}]},"id":null,"style":"Inner","span":{"lo":0,"hi":0}}],"span":{"lo":0,"hi":0},"proc_macros":[]}
+{"module":{"inner":{"lo":0,"hi":0},"unsafety":"No","items":[{"attrs":[],"id":0,"span":{"lo":0,"hi":0},"vis":{"node":"Inherited","span":{"lo":0,"hi":0}},"ident":{"name":"core","span":{"lo":0,"hi":0}},"kind":{"variant":"ExternCrate","fields":[null]},"tokens":null}],"inline":true},"attrs":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"crate_type","span":{"lo":0,"hi":0}},"id":0,"args":null}]},"args":{"variant":"Eq","fields":[{"lo":0,"hi":0},{"0":[[{"variant":"Token","fields":[{"kind":{"variant":"Literal","fields":[{"kind":"Str","symbol":"lib","suffix":null}]},"span":{"lo":0,"hi":0}}]},"Alone"]]}]}}]},"id":null,"style":"Inner","span":{"lo":0,"hi":0}}],"span":{"lo":0,"hi":0},"proc_macros":[]}