Auto merge of #51496 - petrochenkov:mhelper2, r=nikomatsakis

Implement `#[macro_export(local_inner_macros)]` (a solution for the macro helper import problem)

Implement a solution for the macro helper issue discussed in #35896 as described in #35896 (comment).

Macros exported from libraries can be marked with `#[macro_export(local_inner_macros)]` and this annotation changes how nested macros in them are resolved.

If we have a fn-like macro call `ident!(...)` and `ident` comes from a `macro_rules!` macro marked with  `#[macro_export(local_inner_macros)]` then it's replaced with `$crate::ident!(...)` and resolved as such (`$crate` gets the same context as `ident`).

Author: bors

src/librustc/hir/lowering.rs

@@ -616,6 +616,7 @@ impl<'a> LoweringContext<'a> {
             format: codemap::CompilerDesugaring(reason),
             allow_internal_unstable: true,
             allow_internal_unsafe: false,
+            local_inner_macros: false,
             edition: codemap::hygiene::default_edition(),
         });
         span.with_ctxt(SyntaxContext::empty().apply_mark(mark))

src/librustc/ich/impls_syntax.rs

@@ -395,6 +395,7 @@ impl_stable_hash_for!(struct ::syntax_pos::hygiene::ExpnInfo {
     format,
     allow_internal_unstable,
     allow_internal_unsafe,
+    local_inner_macros,
     edition
 });
 

src/librustc_allocator/expand.rs

@@ -103,6 +103,7 @@ impl<'a> Folder for ExpandAllocatorDirectives<'a> {
             format: MacroAttribute(Symbol::intern(name)),
             allow_internal_unstable: true,
             allow_internal_unsafe: false,
+            local_inner_macros: false,
             edition: hygiene::default_edition(),
         });
 

src/librustc_plugin/registry.rs

@@ -108,6 +108,7 @@ impl<'a> Registry<'a> {
                 def_info: _,
                 allow_internal_unstable,
                 allow_internal_unsafe,
+                local_inner_macros,
                 unstable_feature,
                 edition,
             } => {
@@ -117,6 +118,7 @@ impl<'a> Registry<'a> {
                     def_info: Some((nid, self.krate_span)),
                     allow_internal_unstable,
                     allow_internal_unsafe,
+                    local_inner_macros,
                     unstable_feature,
                     edition,
                 }
@@ -152,6 +154,7 @@ impl<'a> Registry<'a> {
             def_info: None,
             allow_internal_unstable: false,
             allow_internal_unsafe: false,
+            local_inner_macros: false,
             unstable_feature: None,
             edition: hygiene::default_edition(),
         });

src/librustc_resolve/macros.rs

@@ -451,11 +451,18 @@ impl<'a> Resolver<'a> {
                                   kind: MacroKind, force: bool)
                                   -> Result<Def, Determinacy> {
         let ast::Path { ref segments, span } = *path;
-        let path: Vec<_> = segments.iter().map(|seg| seg.ident).collect();
+        let mut path: Vec<_> = segments.iter().map(|seg| seg.ident).collect();
         let invocation = self.invocations[&scope];
         let module = invocation.module.get();
         self.current_module = if module.is_trait() { module.parent.unwrap() } else { module };
 
+        // Possibly apply the macro helper hack
+        if self.use_extern_macros && kind == MacroKind::Bang && path.len() == 1 &&
+           path[0].span.ctxt().outer().expn_info().map_or(false, |info| info.local_inner_macros) {
+            let root = Ident::new(keywords::DollarCrate.name(), path[0].span);
+            path.insert(0, root);
+        }
+
         if path.len() > 1 {
             if !self.use_extern_macros && self.gated_errors.insert(span) {
                 let msg = "non-ident macro paths are experimental";

src/libsyntax/ext/base.rs

@@ -621,6 +621,9 @@ pub enum SyntaxExtension {
         /// Whether the contents of the macro can use `unsafe`
         /// without triggering the `unsafe_code` lint.
         allow_internal_unsafe: bool,
+        /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
+        /// for a given macro.
+        local_inner_macros: bool,
         /// The macro's feature name if it is unstable, and the stability feature
         unstable_feature: Option<(Symbol, u32)>,
         /// Edition of the crate in which the macro is defined

src/libsyntax/ext/derive.rs

@@ -64,6 +64,7 @@ pub fn add_derived_markers<T>(cx: &mut ExtCtxt, span: Span, traits: &[ast::Path]
         format: ExpnFormat::MacroAttribute(Symbol::intern(&pretty_name)),
         allow_internal_unstable: true,
         allow_internal_unsafe: false,
+        local_inner_macros: false,
         edition: hygiene::default_edition(),
     });
 

src/libsyntax/ext/expand.rs

@@ -542,6 +542,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             format: MacroAttribute(Symbol::intern(&format!("{}", attr.path))),
             allow_internal_unstable: false,
             allow_internal_unsafe: false,
+            local_inner_macros: false,
             edition: ext.edition(),
         });
 
@@ -695,6 +696,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                                           def_site_span: Option<Span>,
                                           allow_internal_unstable,
                                           allow_internal_unsafe,
+                                          local_inner_macros,
                                           // can't infer this type
                                           unstable_feature: Option<(Symbol, u32)>,
                                           edition| {
@@ -729,6 +731,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 format: macro_bang_format(path),
                 allow_internal_unstable,
                 allow_internal_unsafe,
+                local_inner_macros,
                 edition,
             });
             Ok(())
@@ -737,7 +740,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         let opt_expanded = match *ext {
             DeclMacro(ref expand, def_span, edition) => {
                 if let Err(dummy_span) = validate_and_set_expn_info(self, def_span.map(|(_, s)| s),
-                                                                    false, false, None,
+                                                                    false, false, false, None,
                                                                     edition) {
                     dummy_span
                 } else {
@@ -750,12 +753,14 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 def_info,
                 allow_internal_unstable,
                 allow_internal_unsafe,
+                local_inner_macros,
                 unstable_feature,
                 edition,
             } => {
                 if let Err(dummy_span) = validate_and_set_expn_info(self, def_info.map(|(_, s)| s),
                                                                     allow_internal_unstable,
                                                                     allow_internal_unsafe,
+                                                                    local_inner_macros,
                                                                     unstable_feature,
                                                                     edition) {
                     dummy_span
@@ -777,6 +782,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         format: macro_bang_format(path),
                         allow_internal_unstable,
                         allow_internal_unsafe: false,
+                        local_inner_macros: false,
                         edition: hygiene::default_edition(),
                     });
 
@@ -816,6 +822,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         // FIXME probably want to follow macro_rules macros here.
                         allow_internal_unstable,
                         allow_internal_unsafe: false,
+                        local_inner_macros: false,
                         edition,
                     });
 
@@ -890,6 +897,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             format: MacroAttribute(pretty_name),
             allow_internal_unstable: false,
             allow_internal_unsafe: false,
+            local_inner_macros: false,
             edition: ext.edition(),
         };
 

src/libsyntax/ext/tt/macro_rules.rs

@@ -286,6 +286,12 @@ pub fn compile(sess: &ParseSess, features: &Features, def: &ast::Item, edition:
     if body.legacy {
         let allow_internal_unstable = attr::contains_name(&def.attrs, "allow_internal_unstable");
         let allow_internal_unsafe = attr::contains_name(&def.attrs, "allow_internal_unsafe");
+        let mut local_inner_macros = false;
+        if let Some(macro_export) = attr::find_by_name(&def.attrs, "macro_export") {
+            if let Some(l) = macro_export.meta_item_list() {
+                local_inner_macros = attr::list_contains_name(&l, "local_inner_macros");
+            }
+        }
 
         let unstable_feature = attr::find_stability(&sess.span_diagnostic,
                                                     &def.attrs, def.span).and_then(|stability| {
@@ -301,6 +307,7 @@ pub fn compile(sess: &ParseSess, features: &Features, def: &ast::Item, edition:
             def_info: Some((def.id, def.span)),
             allow_internal_unstable,
             allow_internal_unsafe,
+            local_inner_macros,
             unstable_feature,
             edition,
         }

src/libsyntax/std_inject.rs

@@ -29,6 +29,7 @@ fn ignored_span(sp: Span) -> Span {
         format: MacroAttribute(Symbol::intern("std_inject")),
         allow_internal_unstable: true,
         allow_internal_unsafe: false,
+        local_inner_macros: false,
         edition: hygiene::default_edition(),
     });
     sp.with_ctxt(SyntaxContext::empty().apply_mark(mark))

src/libsyntax/test.rs

@@ -311,6 +311,7 @@ fn generate_test_harness(sess: &ParseSess,
         format: MacroAttribute(Symbol::intern("test")),
         allow_internal_unstable: true,
         allow_internal_unsafe: false,
+        local_inner_macros: false,
         edition: hygiene::default_edition(),
     });
 

src/libsyntax_ext/lib.rs

@@ -76,6 +76,7 @@ pub fn register_builtins(resolver: &mut syntax::ext::base::Resolver,
                         def_info: None,
                         allow_internal_unstable: false,
                         allow_internal_unsafe: false,
+                        local_inner_macros: false,
                         unstable_feature: None,
                         edition: hygiene::default_edition(),
                     });
@@ -132,6 +133,7 @@ pub fn register_builtins(resolver: &mut syntax::ext::base::Resolver,
                 def_info: None,
                 allow_internal_unstable: true,
                 allow_internal_unsafe: false,
+                local_inner_macros: false,
                 unstable_feature: None,
                 edition: hygiene::default_edition(),
             });

src/libsyntax_ext/proc_macro_registrar.rs

@@ -368,6 +368,7 @@ fn mk_registrar(cx: &mut ExtCtxt,
         format: MacroAttribute(Symbol::intern("proc_macro")),
         allow_internal_unstable: true,
         allow_internal_unsafe: false,
+        local_inner_macros: false,
         edition: hygiene::default_edition(),
     });
     let span = DUMMY_SP.apply_mark(mark);

src/libsyntax_pos/hygiene.rs

@@ -496,6 +496,9 @@ pub struct ExpnInfo {
     /// Whether the macro is allowed to use `unsafe` internally
     /// even if the user crate has `#![forbid(unsafe_code)]`.
     pub allow_internal_unsafe: bool,
+    /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
+    /// for a given macro.
+    pub local_inner_macros: bool,
     /// Edition of the crate in which the macro is defined.
     pub edition: Edition,
 }

src/test/run-pass-fulldeps/auxiliary/plugin_args.rs

@@ -54,6 +54,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
             def_info: None,
             allow_internal_unstable: false,
             allow_internal_unsafe: false,
+            local_inner_macros: false,
             unstable_feature: None,
             edition: hygiene::default_edition(),
         });

src/test/ui/hygiene/auxiliary/local_inner_macros.rs

@@ -0,0 +1,29 @@
+// Copyright 2018 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.
+
+#[macro_export]
+macro_rules! helper1 {
+    () => ( struct S; )
+}
+
+#[macro_export(local_inner_macros)]
+macro_rules! helper2 {
+    () => ( helper1!(); )
+}
+
+#[macro_export(local_inner_macros)]
+macro_rules! public_macro {
+    () => ( helper2!(); )
+}
+
+#[macro_export(local_inner_macros)]
+macro_rules! public_macro_dynamic {
+    ($helper: ident) => ( $helper!(); )
+}

src/test/ui/hygiene/local_inner_macros.rs

@@ -0,0 +1,31 @@
+// Copyright 2018 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.
+
+// compile-pass
+// aux-build:local_inner_macros.rs
+
+#![feature(use_extern_macros)]
+
+extern crate local_inner_macros;
+
+use local_inner_macros::{public_macro, public_macro_dynamic};
+
+public_macro!();
+
+macro_rules! local_helper {
+    () => ( struct Z; )
+}
+
+public_macro_dynamic!(local_helper);
+
+fn main() {
+    let s = S;
+    let z = Z;
+}

src/test/ui/hygiene/local_inner_macros_disabled.rs

@@ -0,0 +1,21 @@
+// Copyright 2018 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.
+
+// `local_inner_macros` has no effect if `feature(use_extern_macros)` is not enabled
+
+// aux-build:local_inner_macros.rs
+// error-pattern: cannot find macro `helper2!` in this scope
+
+#[macro_use(public_macro)]
+extern crate local_inner_macros;
+
+public_macro!();
+
+fn main() {}

src/test/ui/hygiene/local_inner_macros_disabled.stderr

@@ -0,0 +1,10 @@
+error: cannot find macro `helper2!` in this scope
+  --> $DIR/local_inner_macros_disabled.rs:19:1
+   |
+LL | public_macro!();
+   | ^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+
+error: aborting due to previous error
+