Auto merge of rust-lang#84113 - SNCPlay42:suggestion-extern-crate, r=petrochenkov

Detect when suggested paths enter extern crates more rigorously

When reporting resolution errors, the compiler tries to avoid suggesting importing inaccessible paths from other crates. However, the search for suggestions only recognized when it was entering a crate root directly, and so failed to recognize a path like `crate::module::private_item`, where `module` was imported from another crate with `use other_crate::module`, as entering another crate.

Fixes rust-lang#80079
Fixes rust-lang#84081

Author: bors

compiler/rustc_resolve/src/diagnostics.rs

@@ -758,17 +758,14 @@ impl<'a> Resolver<'a> {
     {
         let mut candidates = Vec::new();
         let mut seen_modules = FxHashSet::default();
-        let not_local_module = crate_name.name != kw::Crate;
-        let mut worklist =
-            vec![(start_module, Vec::<ast::PathSegment>::new(), true, not_local_module)];
+        let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), true)];
         let mut worklist_via_import = vec![];
 
-        while let Some((in_module, path_segments, accessible, in_module_is_extern)) =
-            match worklist.pop() {
-                None => worklist_via_import.pop(),
-                Some(x) => Some(x),
-            }
-        {
+        while let Some((in_module, path_segments, accessible)) = match worklist.pop() {
+            None => worklist_via_import.pop(),
+            Some(x) => Some(x),
+        } {
+            let in_module_is_extern = !in_module.def_id().unwrap().is_local();
             // We have to visit module children in deterministic order to avoid
             // instabilities in reported imports (#43552).
             in_module.for_each_child(self, |this, ident, ns, name_binding| {
@@ -850,11 +847,10 @@ impl<'a> Resolver<'a> {
                         name_binding.is_extern_crate() && lookup_ident.span.rust_2018();
 
                     if !is_extern_crate_that_also_appears_in_prelude {
-                        let is_extern = in_module_is_extern || name_binding.is_extern_crate();
                         // add the module to the lookup
                         if seen_modules.insert(module.def_id().unwrap()) {
                             if via_import { &mut worklist_via_import } else { &mut worklist }
-                                .push((module, path_segments, child_accessible, is_extern));
+                                .push((module, path_segments, child_accessible));
                         }
                     }
                 }

src/test/ui/resolve/auxiliary/issue-80079.rs

@@ -0,0 +1,18 @@
+#![crate_type = "lib"]
+
+pub mod public {
+    use private_import;
+
+    // should not be suggested since it is private
+    struct Foo;
+
+    mod private_module {
+        // should not be suggested since it is private
+        pub struct Foo;
+    }
+}
+
+mod private_import {
+    // should not be suggested since it is private
+    pub struct Foo;
+}

src/test/ui/resolve/issue-80079.rs

@@ -0,0 +1,12 @@
+// aux-build:issue-80079.rs
+
+// using a module from another crate should not cause errors to suggest private
+// items in that module
+
+extern crate issue_80079;
+
+use issue_80079::public;
+
+fn main() {
+    let _ = Foo; //~ ERROR cannot find value `Foo` in this scope
+}

src/test/ui/resolve/issue-80079.stderr

@@ -0,0 +1,9 @@
+error[E0425]: cannot find value `Foo` in this scope
+  --> $DIR/issue-80079.rs:11:13
+   |
+LL |     let _ = Foo;
+   |             ^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0425`.