report unused_import for empty reexports even it is pub

Author: bvanjoi

compiler/rustc_resolve/src/check_unused.rs

@@ -173,7 +173,7 @@ impl<'a, 'b, 'tcx> Visitor<'a> for UnusedImportCheckVisitor<'a, 'b, 'tcx> {
             self.base_use_tree = Some(use_tree);
         }
 
-        if self.base_use_is_pub {
+        if self.base_use_is_pub && !self.r.empty_glob_reexports.contains(&id) {
             self.check_import_as_underscore(use_tree, id);
             return;
         }

compiler/rustc_resolve/src/imports.rs

@@ -987,6 +987,10 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                                 candidates: None,
                             });
                         }
+
+                        if self.resolutions(module).borrow().is_empty() {
+                            self.empty_glob_reexports.insert(id);
+                        }
                     }
                     if !is_prelude
                     && let Some(max_vis) = max_vis.get()

compiler/rustc_resolve/src/lib.rs

@@ -1108,6 +1108,9 @@ pub struct Resolver<'a, 'tcx> {
     /// Whether lifetime elision was successful.
     lifetime_elision_allowed: FxHashSet<NodeId>,
 
+    /// These glob imports which doesn't has any reexports
+    empty_glob_reexports: FxHashSet<NodeId>,
+
     /// Names of items that were stripped out via cfg with their corresponding cfg meta item.
     stripped_cfg_items: Vec<StrippedCfgItem<NodeId>>,
 
@@ -1336,6 +1339,8 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             determined_imports: Vec::new(),
             indeterminate_imports: Vec::new(),
 
+            empty_glob_reexports: Default::default(),
+
             pat_span_map: Default::default(),
             partial_res_map: Default::default(),
             import_res_map: Default::default(),

tests/ui/imports/pub-reexport-empty.rs

@@ -0,0 +1,18 @@
+#![deny(unused_imports)]
+
+mod a {}
+
+pub use a::*;
+//~^ ERROR: unused import: `a::*`
+
+mod b {
+    mod c {
+        #[derive(Clone)]
+        pub struct D;
+    }
+    pub use self::c::*; // don't show unused import lint
+}
+
+pub use b::*; // don't show unused import lint
+
+fn main() {}

tests/ui/imports/pub-reexport-empty.stderr

@@ -0,0 +1,14 @@
+error: unused import: `a::*`
+  --> $DIR/pub-reexport-empty.rs:5:9
+   |
+LL | pub use a::*;
+   |         ^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/pub-reexport-empty.rs:1:9
+   |
+LL | #![deny(unused_imports)]
+   |         ^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+