Add feature to set path-based visibility of macro_rules to pub by default

compiler/rustc_feature/src/unstable.rs

@@ -568,6 +568,8 @@ declare_features! (
     (unstable, macro_attr, "1.91.0", Some(143547)),
     /// Allow `macro_rules!` derive rules
     (unstable, macro_derive, "1.91.0", Some(143549)),
+    /// Make `macro_rules!` implicitly pub even without `macro_export`
+    (unstable, macro_implicit_pub, "CURRENT_RUSTC_VERSION", Some(148610)),
     /// Give access to additional metadata about declarative macro meta-variables.
     (unstable, macro_metavar_expr, "1.61.0", Some(83527)),
     /// Provides a way to concatenate identifiers using metavariable expressions.

compiler/rustc_lint/src/builtin.rs

@@ -1288,6 +1288,11 @@ impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
         if let hir::ItemKind::Use(_, hir::UseKind::ListStem) = &item.kind {
             return;
         }
+        // Do not warn for macro_rules definitions which are pub and unreachable by default,
+        // only check their associated use re-exports.
+        if let hir::ItemKind::Macro(_, ast::MacroDef { macro_rules: true, .. }, _) = &item.kind {
+            return;
+        }
         self.perform_lint(cx, "item", item.owner_id.def_id, item.vis_span, true);
     }
 

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -1299,7 +1299,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             let ident = ident.normalize_to_macros_2_0();
             self.r.macro_names.insert(ident);
             let is_macro_export = ast::attr::contains_name(&item.attrs, sym::macro_export);
-            let vis = if is_macro_export {
+            let vis = if is_macro_export || self.r.tcx().features().macro_implicit_pub() {
                 Visibility::Public
             } else {
                 Visibility::Restricted(CRATE_DEF_ID)

compiler/rustc_span/src/symbol.rs

@@ -1380,6 +1380,7 @@ symbols! {
         macro_derive,
         macro_escape,
         macro_export,
+        macro_implicit_pub,
         macro_lifetime_matcher,
         macro_literal_matcher,
         macro_metavar_expr,

tests/ui/feature-gates/feature-gate-macro-implicit-pub.rs

@@ -0,0 +1,8 @@
+//@ edition:2018
+#![crate_type = "lib"]
+
+macro_rules! not_pub {
+    () => {}
+}
+
+pub use not_pub; //~ ERROR: `not_pub` is only public within the crate, and cannot be re-exported outside [E0364]

tests/ui/feature-gates/feature-gate-macro-implicit-pub.stderr

@@ -0,0 +1,21 @@
+error[E0364]: `not_pub` is only public within the crate, and cannot be re-exported outside
+  --> $DIR/feature-gate-macro-implicit-pub.rs:8:9
+   |
+LL | pub use not_pub;
+   |         ^^^^^^^
+   |
+help: consider adding a `#[macro_export]` to the macro in the imported module
+  --> $DIR/feature-gate-macro-implicit-pub.rs:4:1
+   |
+LL | / macro_rules! not_pub {
+LL | |     () => {}
+LL | | }
+   | |_^
+help: in case you want to use the macro within this crate only, reduce the visibility to `pub(crate)`
+   |
+LL | pub(crate) use not_pub;
+   |    +++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0364`.

tests/ui/macros/auxiliary/implicit-pub.rs

@@ -0,0 +1,16 @@
+//@ edition:2018
+#![feature(macro_implicit_pub)]
+#[allow(unused_macros)]
+macro_rules! fake_pub {
+    () => {}
+}
+
+macro_rules! real_pub {
+    () => {}
+}
+
+pub mod inner {
+    pub use real_pub;
+}
+
+pub use real_pub as real_pub_reexport;

tests/ui/macros/implicit-pub-macros2-linted-still.rs

@@ -0,0 +1,10 @@
+//@ edition:2018
+#![feature(decl_macro)]
+#![crate_type = "lib"]
+#![deny(unreachable_pub)]
+
+mod inner {
+    pub macro m($inner_str:expr) { //~ ERROR: unreachable `pub` item [unreachable_pub]
+        struct S;
+    }
+}

tests/ui/macros/implicit-pub-macros2-linted-still.stderr

@@ -0,0 +1,17 @@
+error: unreachable `pub` item
+  --> $DIR/implicit-pub-macros2-linted-still.rs:7:5
+   |
+LL |     pub macro m($inner_str:expr) {
+   |     ---^^^^^^^^
+   |     |
+   |     help: consider restricting its visibility: `pub(crate)`
+   |
+   = help: or consider exporting it for use by other crates
+note: the lint level is defined here
+  --> $DIR/implicit-pub-macros2-linted-still.rs:4:9
+   |
+LL | #![deny(unreachable_pub)]
+   |         ^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/macros/implicit-pub-still-unreachable.rs

@@ -0,0 +1,8 @@
+//@ aux-build:implicit-pub.rs
+//@ edition:2018
+
+extern crate implicit_pub;
+
+fn main() {
+    implicit_pub::inner::fake_pub!(); //~ error: failed to resolve: could not find `fake_pub` in `inner` [E0433]
+}

tests/ui/macros/implicit-pub-still-unreachable.stderr

@@ -0,0 +1,9 @@
+error[E0433]: failed to resolve: could not find `fake_pub` in `inner`
+  --> $DIR/implicit-pub-still-unreachable.rs:7:26
+   |
+LL |     implicit_pub::inner::fake_pub!();
+   |                          ^^^^^^^^ could not find `fake_pub` in `inner`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0433`.

tests/ui/macros/implicit-pub-unreachable-lint.rs

@@ -0,0 +1,12 @@
+//@ edition:2018
+#![crate_type = "lib"]
+#![feature(macro_implicit_pub)]
+#![deny(unreachable_pub)]
+
+macro_rules! not_reexported {
+    () => {}
+}
+
+mod inner {
+    pub use not_reexported; //~ ERROR: unreachable `pub` item [unreachable_pub]
+}

tests/ui/macros/implicit-pub-unreachable-lint.stderr

@@ -0,0 +1,17 @@
+error: unreachable `pub` item
+  --> $DIR/implicit-pub-unreachable-lint.rs:11:13
+   |
+LL |     pub use not_reexported;
+   |     ---     ^^^^^^^^^^^^^^
+   |     |
+   |     help: consider restricting its visibility: `pub(crate)`
+   |
+   = help: or consider exporting it for use by other crates
+note: the lint level is defined here
+  --> $DIR/implicit-pub-unreachable-lint.rs:4:9
+   |
+LL | #![deny(unreachable_pub)]
+   |         ^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/macros/implicit-pub-unreachable-no-lint.rs

@@ -0,0 +1,7 @@
+//@ check-pass
+//@ edition:2018
+#![crate_type = "lib"]
+
+macro_rules! not_reexported {
+    () => {}
+}

tests/ui/macros/implicit-pub.rs

@@ -0,0 +1,10 @@
+//@ check-pass
+//@ aux-build:implicit-pub.rs
+//@ edition:2018
+
+extern crate implicit_pub;
+
+fn main() {
+    implicit_pub::inner::real_pub!();
+    implicit_pub::real_pub_reexport!();
+}