Syntactically permit unsafety on mods

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":[]}

src/test/ui/ast-json/ast-json-output.stdout

@@ -1 +1 @@
-{"module":{"inner":{"lo":0,"hi":0},"items":[{"attrs":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"prelude_import","span":{"lo":0,"hi":0}},"id":0,"args":null}]},"args":"Empty"}]},"id":null,"style":"Outer","span":{"lo":0,"hi":0}}],"id":0,"span":{"lo":0,"hi":0},"vis":{"node":"Inherited","span":{"lo":0,"hi":0}},"ident":{"name":"","span":{"lo":0,"hi":0}},"kind":{"variant":"Use","fields":[{"prefix":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"{{root}}","span":{"lo":0,"hi":0}},"id":0,"args":null},{"ident":{"name":"std","span":{"lo":0,"hi":0}},"id":0,"args":null},{"ident":{"name":"prelude","span":{"lo":0,"hi":0}},"id":0,"args":null},{"ident":{"name":"v1","span":{"lo":0,"hi":0}},"id":0,"args":null}]},"kind":"Glob","span":{"lo":0,"hi":0}}]},"tokens":null},{"attrs":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"macro_use","span":{"lo":0,"hi":0}},"id":0,"args":null}]},"args":"Empty"}]},"id":null,"style":"Outer","span":{"lo":0,"hi":0}}],"id":0,"span":{"lo":0,"hi":0},"vis":{"node":"Inherited","span":{"lo":0,"hi":0}},"ident":{"name":"std","span":{"lo":0,"hi":0}},"kind":{"variant":"ExternCrate","fields":[null]},"tokens":null},{"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":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"prelude_import","span":{"lo":0,"hi":0}},"id":0,"args":null}]},"args":"Empty"}]},"id":null,"style":"Outer","span":{"lo":0,"hi":0}}],"id":0,"span":{"lo":0,"hi":0},"vis":{"node":"Inherited","span":{"lo":0,"hi":0}},"ident":{"name":"","span":{"lo":0,"hi":0}},"kind":{"variant":"Use","fields":[{"prefix":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"{{root}}","span":{"lo":0,"hi":0}},"id":0,"args":null},{"ident":{"name":"std","span":{"lo":0,"hi":0}},"id":0,"args":null},{"ident":{"name":"prelude","span":{"lo":0,"hi":0}},"id":0,"args":null},{"ident":{"name":"v1","span":{"lo":0,"hi":0}},"id":0,"args":null}]},"kind":"Glob","span":{"lo":0,"hi":0}}]},"tokens":null},{"attrs":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"macro_use","span":{"lo":0,"hi":0}},"id":0,"args":null}]},"args":"Empty"}]},"id":null,"style":"Outer","span":{"lo":0,"hi":0}}],"id":0,"span":{"lo":0,"hi":0},"vis":{"node":"Inherited","span":{"lo":0,"hi":0}},"ident":{"name":"std","span":{"lo":0,"hi":0}},"kind":{"variant":"ExternCrate","fields":[null]},"tokens":null},{"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":[]}

src/test/ui/parser/unsafe-foreign-mod.rs

@@ -0,0 +1,9 @@
+unsafe extern {
+    //~^ ERROR extern block cannot be declared unsafe
+}
+
+unsafe extern "C" {
+    //~^ ERROR extern block cannot be declared unsafe
+}
+
+fn main() {}

src/test/ui/parser/unsafe-foreign-mod.stderr

@@ -0,0 +1,14 @@
+error: extern block cannot be declared unsafe
+  --> $DIR/unsafe-foreign-mod.rs:1:1
+   |
+LL | unsafe extern {
+   | ^^^^^^
+
+error: extern block cannot be declared unsafe
+  --> $DIR/unsafe-foreign-mod.rs:5:1
+   |
+LL | unsafe extern "C" {
+   | ^^^^^^
+
+error: aborting due to 2 previous errors
+

src/test/ui/parser/unsafe-mod.rs

@@ -0,0 +1,9 @@
+unsafe mod m {
+    //~^ ERROR module cannot be declared unsafe
+}
+
+unsafe mod n;
+//~^ ERROR module cannot be declared unsafe
+//~^^ ERROR file not found for module `n`
+
+fn main() {}

src/test/ui/parser/unsafe-mod.stderr

@@ -0,0 +1,23 @@
+error[E0583]: file not found for module `n`
+  --> $DIR/unsafe-mod.rs:5:1
+   |
+LL | unsafe mod n;
+   | ^^^^^^^^^^^^^
+   |
+   = help: to create the module `n`, create file "$DIR/n.rs"
+
+error: module cannot be declared unsafe
+  --> $DIR/unsafe-mod.rs:1:1
+   |
+LL | unsafe mod m {
+   | ^^^^^^
+
+error: module cannot be declared unsafe
+  --> $DIR/unsafe-mod.rs:5:1
+   |
+LL | unsafe mod n;
+   | ^^^^^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0583`.

src/test/ui/proc-macro/auxiliary/macro-only-syntax.rs

@@ -0,0 +1,89 @@
+// force-host
+// no-prefer-dynamic
+
+// These are tests for syntax that is accepted by the Rust parser but
+// unconditionally rejected semantically after macro expansion. Attribute macros
+// are permitted to accept such syntax as long as they replace it with something
+// that makes sense to Rust.
+//
+// We also inspect some of the spans to verify the syntax is not triggering the
+// lossy string reparse hack (https://github.com/rust-lang/rust/issues/43081).
+
+#![crate_type = "proc-macro"]
+#![feature(proc_macro_span)]
+
+extern crate proc_macro;
+use proc_macro::{token_stream, Delimiter, TokenStream, TokenTree};
+use std::path::Component;
+
+// unsafe mod m {
+//     pub unsafe mod inner;
+// }
+#[proc_macro_attribute]
+pub fn expect_unsafe_mod(_attrs: TokenStream, input: TokenStream) -> TokenStream {
+    let tokens = &mut input.into_iter();
+    expect(tokens, "unsafe");
+    expect(tokens, "mod");
+    expect(tokens, "m");
+    let tokens = &mut expect_brace(tokens);
+    expect(tokens, "pub");
+    expect(tokens, "unsafe");
+    expect(tokens, "mod");
+    let ident = expect(tokens, "inner");
+    expect(tokens, ";");
+    check_useful_span(ident, "unsafe-mod.rs");
+    TokenStream::new()
+}
+
+// unsafe extern {
+//     type T;
+// }
+#[proc_macro_attribute]
+pub fn expect_unsafe_foreign_mod(_attrs: TokenStream, input: TokenStream) -> TokenStream {
+    let tokens = &mut input.into_iter();
+    expect(tokens, "unsafe");
+    expect(tokens, "extern");
+    let tokens = &mut expect_brace(tokens);
+    expect(tokens, "type");
+    let ident = expect(tokens, "T");
+    expect(tokens, ";");
+    check_useful_span(ident, "unsafe-foreign-mod.rs");
+    TokenStream::new()
+}
+
+// unsafe extern "C++" {}
+#[proc_macro_attribute]
+pub fn expect_unsafe_extern_cpp_mod(_attrs: TokenStream, input: TokenStream) -> TokenStream {
+    let tokens = &mut input.into_iter();
+    expect(tokens, "unsafe");
+    expect(tokens, "extern");
+    let abi = expect(tokens, "\"C++\"");
+    expect_brace(tokens);
+    check_useful_span(abi, "unsafe-foreign-mod.rs");
+    TokenStream::new()
+}
+
+fn expect(tokens: &mut token_stream::IntoIter, expected: &str) -> TokenTree {
+    match tokens.next() {
+        Some(token) if token.to_string() == expected => token,
+        wrong => panic!("unexpected token: {:?}, expected `{}`", wrong, expected),
+    }
+}
+
+fn expect_brace(tokens: &mut token_stream::IntoIter) -> token_stream::IntoIter {
+    match tokens.next() {
+        Some(TokenTree::Group(group)) if group.delimiter() == Delimiter::Brace => {
+            group.stream().into_iter()
+        }
+        wrong => panic!("unexpected token: {:?}, expected `{{`", wrong),
+    }
+}
+
+fn check_useful_span(token: TokenTree, expected_filename: &str) {
+    let span = token.span();
+    assert!(span.start().column < span.end().column);
+
+    let source_path = span.source_file().path();
+    let filename = source_path.components().last().unwrap();
+    assert_eq!(filename, Component::Normal(expected_filename.as_ref()));
+}

src/test/ui/proc-macro/unsafe-foreign-mod.rs

@@ -0,0 +1,14 @@
+// run-pass
+// aux-build:macro-only-syntax.rs
+
+extern crate macro_only_syntax;
+
+#[macro_only_syntax::expect_unsafe_foreign_mod]
+unsafe extern {
+    type T;
+}
+
+#[macro_only_syntax::expect_unsafe_extern_cpp_mod]
+unsafe extern "C++" {}
+
+fn main() {}

src/test/ui/proc-macro/unsafe-mod.rs

@@ -0,0 +1,13 @@
+// run-pass
+// aux-build:macro-only-syntax.rs
+
+#![feature(proc_macro_hygiene)]
+
+extern crate macro_only_syntax;
+
+#[macro_only_syntax::expect_unsafe_mod]
+unsafe mod m {
+    pub unsafe mod inner;
+}
+
+fn main() {}