resolve: Mark more erroneous imports as used

Author: petrochenkov

Diff for: src/librustc_resolve/resolve_imports.rs

@@ -673,6 +673,10 @@ impl<'a, 'b> ImportResolver<'a, 'b> {
             self.throw_unresolved_import_error(errors.clone(), None);
         }
 
+        for import in &self.r.indeterminate_imports {
+            // Consider erroneous imports used to avoid duplicate diagnostics.
+            self.r.used_imports.insert((import.id, TypeNS));
+        }
         // Report unresolved imports only if no hard error was already reported
         // to avoid generating multiple errors on the same import.
         if !has_errors {
@@ -839,6 +843,10 @@ impl<'a, 'b> ImportResolver<'a, 'b> {
                                          true, directive.span, directive.crate_lint());
         let no_ambiguity = self.r.ambiguity_errors.len() == prev_ambiguity_errors_len;
         directive.vis.set(orig_vis);
+        if let PathResult::Failed { .. } | PathResult::NonModule(..) = path_res {
+            // Consider erroneous imports used to avoid duplicate diagnostics.
+            self.r.used_imports.insert((directive.id, TypeNS));
+        }
         let module = match path_res {
             PathResult::Module(module) => {
                 // Consistency checks, analogous to `finalize_macro_resolutions`.

Diff for: src/test/ui/imports/unresolved-imports-used.rs

@@ -1,12 +1,18 @@
-// There should be *no* unused import errors.
+// There should be *one* unused import error.
 #![deny(unused_imports)]
 
 mod qux {
    fn quz() {}
+   pub fn quy() {}
 }
 
-use qux::quz; //~ ERROR function `quz` is private
-use qux::bar; //~ ERROR unresolved import `qux::bar`
-use foo::bar; //~ ERROR unresolved import `foo`
+use qux::quz;  //~ ERROR function `quz` is private
+use qux::bar;  //~ ERROR unresolved import `qux::bar`
+use foo::bar;
+use baz::*;
+use qux::bar2; //~ ERROR unresolved import `qux::bar2`
+use foo2::bar2;
+use baz2::*;
+use qux::quy;  //~ ERROR unused import
 
 fn main() {}

Diff for: src/test/ui/imports/unresolved-imports-used.stderr

@@ -1,22 +1,34 @@
 error[E0432]: unresolved import `qux::bar`
-  --> $DIR/unresolved-imports-used.rs:9:5
+  --> $DIR/unresolved-imports-used.rs:10:5
    |
 LL | use qux::bar;
    |     ^^^^^^^^ no `bar` in `qux`
 
-error[E0432]: unresolved import `foo`
-  --> $DIR/unresolved-imports-used.rs:10:5
+error[E0432]: unresolved import `qux::bar2`
+  --> $DIR/unresolved-imports-used.rs:13:5
    |
-LL | use foo::bar;
-   |     ^^^ maybe a missing crate `foo`?
+LL | use qux::bar2;
+   |     ^^^^^^^^^ no `bar2` in `qux`
 
 error[E0603]: function `quz` is private
-  --> $DIR/unresolved-imports-used.rs:8:10
+  --> $DIR/unresolved-imports-used.rs:9:10
    |
 LL | use qux::quz;
    |          ^^^
 
-error: aborting due to 3 previous errors
+error: unused import: `qux::quy`
+  --> $DIR/unresolved-imports-used.rs:16:5
+   |
+LL | use qux::quy;
+   |     ^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/unresolved-imports-used.rs:2:9
+   |
+LL | #![deny(unused_imports)]
+   |         ^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors
 
 Some errors have detailed explanations: E0432, E0603.
 For more information about an error, try `rustc --explain E0432`.