resolve: Catch "cannot reexport" errors from macros 2.0 better

Author: petrochenkov

compiler/rustc_resolve/src/imports.rs

@@ -787,6 +787,29 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 let resolution = resolution.borrow();
                 let Some(binding) = resolution.best_decl() else { continue };
 
+                // Report "cannot reexport" errors for exotic cases involving macros 2.0
+                // privacy bending or invariant-breaking code under deprecation lints.
+                for decl in [resolution.non_glob_decl, resolution.glob_decl] {
+                    if let Some(decl) = decl
+                        && let DeclKind::Import { source_decl, import } = decl.kind
+                    {
+                        // The source entity is too private to be reexported
+                        // with the given import declaration's visibility.
+                        let ord = source_decl.vis().partial_cmp(decl.vis(), self.tcx);
+                        if matches!(ord, None | Some(Ordering::Less)) {
+                            let ident = match import.kind {
+                                ImportKind::Single { source, .. } => source,
+                                _ => key.ident.orig(resolution.orig_ident_span),
+                            };
+                            if let Some(lint) =
+                                self.report_cannot_reexport(import, source_decl, ident, key.ns)
+                            {
+                                self.lint_buffer.add_early_lint(lint);
+                            }
+                        }
+                    }
+                }
+
                 if let DeclKind::Import { import, .. } = binding.kind
                     && let Some(amb_binding) = binding.ambiguity.get()
                     && binding.res() != Res::Err
@@ -1498,18 +1521,20 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let mut reexport_error = None;
         let mut any_successful_reexport = false;
         self.per_ns(|this, ns| {
-            let Some(binding) = bindings[ns].get().decl().map(|b| b.import_source()) else {
+            let Some(binding) = bindings[ns].get().decl() else {
                 return;
             };
 
             if import.vis.greater_than(binding.vis(), this.tcx) {
-                reexport_error = Some((ns, binding));
+                // In isolation, a declaration like this is not an error, but if *all* 1-3
+                // declarations introduced by the import are more private than the import item's
+                // nominal visibility, then it's an error.
+                reexport_error = Some((ns, binding.import_source()));
             } else {
                 any_successful_reexport = true;
             }
         });
 
-        // All namespaces must be re-exported with extra visibility for an error to occur.
         if !any_successful_reexport {
             let (ns, binding) = reexport_error.unwrap();
             if let Some(lint) = self.report_cannot_reexport(import, binding, ident, ns) {

tests/ui/hygiene/privacy-early.rs

@@ -8,6 +8,7 @@ mod foo {
 
     pub macro m() {
         use f as g; //~ ERROR `f` is private, and cannot be re-exported
+                    //~| ERROR `f` is private, and cannot be re-exported
         f!();
     }
 }

tests/ui/hygiene/privacy-early.stderr

@@ -17,6 +17,26 @@ LL |     foo::m!();
    |     --------- in this macro invocation
    = note: this error originates in the macro `foo::m` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 1 previous error
+error[E0364]: `f` is private, and cannot be re-exported
+  --> $DIR/privacy-early.rs:10:13
+   |
+LL |         use f as g;
+   |             ^^^^^^
+...
+LL |     foo::m!();
+   |     --------- in this macro invocation
+   |
+note: consider marking `f` as `pub` in the imported module
+  --> $DIR/privacy-early.rs:10:13
+   |
+LL |         use f as g;
+   |             ^^^^^^
+...
+LL |     foo::m!();
+   |     --------- in this macro invocation
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+   = note: this error originates in the macro `foo::m` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0364`.

tests/ui/imports/private-from-decl-macro.fail.stderr

@@ -1,5 +1,24 @@
+error[E0364]: `S` is private, and cannot be re-exported
+  --> $DIR/private-from-decl-macro.rs:18:13
+   |
+LL |         use crate::m::*;
+   |             ^^^^^^^^^^^
+...
+LL |     crate::m::mac_glob!();
+   |     --------------------- in this macro invocation
+   |
+note: consider marking `S` as `pub` in the imported module
+  --> $DIR/private-from-decl-macro.rs:18:13
+   |
+LL |         use crate::m::*;
+   |             ^^^^^^^^^^^
+...
+LL |     crate::m::mac_glob!();
+   |     --------------------- in this macro invocation
+   = note: this error originates in the macro `crate::m::mac_glob` (in Nightly builds, run with -Z macro-backtrace for more info)
+
 error[E0423]: expected value, found struct `S`
-  --> $DIR/private-from-decl-macro.rs:27:17
+  --> $DIR/private-from-decl-macro.rs:28:17
    |
 LL |     pub struct S {}
    |     --------------- `S` defined here
@@ -22,6 +41,7 @@ LL -         let s = S;
 LL +         let s = s;
    |
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0423`.
+Some errors have detailed explanations: E0364, E0423.
+For more information about an error, try `rustc --explain E0364`.

tests/ui/imports/private-from-decl-macro.rs

@@ -14,7 +14,8 @@ mod m {
     }
 
     pub macro mac_glob() {
-        use crate::m::*;
+        #[cfg(fail)]
+        use crate::m::*; //[fail]~ ERROR `S` is private, and cannot be re-exported
     }
 }