Elide unused import errors for failed use statements

Author: estebank

src/librustc_resolve/check_unused.rs

@@ -26,7 +26,7 @@
 use std::ops::{Deref, DerefMut};
 
 use crate::Resolver;
-use crate::resolve_imports::ImportDirectiveSubclass;
+use crate::resolve_imports::{ImportDirective, ImportDirectiveSubclass};
 
 use rustc::util::nodemap::NodeMap;
 use rustc::{lint, ty};
@@ -283,7 +283,15 @@ pub fn check_crate(resolver: &mut Resolver<'_>, krate: &ast::Crate) {
     };
     visit::walk_crate(&mut visitor, krate);
 
-    for unused in visitor.unused_imports.values() {
+    let mut silencing_spans: Vec<Span> = visitor.privacy_errors
+        .iter()
+        .map(|crate::PrivacyError(span, _, _)| span)
+        .chain(visitor.indeterminate_imports.iter().map(|ImportDirective { span, .. }| span))
+        .chain(visitor.unresolved_imports.iter())
+        .map(|sp| *sp)
+        .collect();
+
+    'unused_imports: for unused in visitor.unused_imports.values() {
         let mut fixes = Vec::new();
         let mut spans = match calc_unused_spans(unused, unused.use_tree, unused.use_tree_id) {
             UnusedSpanResult::Used => continue,
@@ -305,6 +313,20 @@ pub fn check_crate(resolver: &mut Resolver<'_>, krate: &ast::Crate) {
 
         let len = spans.len();
         spans.sort();
+        for sp in &spans {
+            // Do not emit unused warnings about failed use statements (#48244)
+            let mut idx = None;
+            for (i, span) in silencing_spans.iter().enumerate() {
+                if sp.overlaps(*span) {
+                    idx = Some(i);
+                    break;
+                }
+            }
+            if let Some(idx) = idx {
+                silencing_spans.remove(idx);  // we won't be seeing this again
+                continue 'unused_imports;
+            }
+        }
         let ms = MultiSpan::from_spans(spans.clone());
         let mut span_snippets = spans.iter()
             .filter_map(|s| {

src/librustc_resolve/lib.rs

@@ -1555,6 +1555,7 @@ pub struct Resolver<'a> {
 
     /// All non-determined imports.
     indeterminate_imports: Vec<&'a ImportDirective<'a>>,
+    unresolved_imports: Vec<Span>,
 
     /// The module that represents the current item scope.
     current_module: Module<'a>,
@@ -1924,6 +1925,7 @@ impl<'a> Resolver<'a> {
 
             determined_imports: Vec::new(),
             indeterminate_imports: Vec::new(),
+            unresolved_imports: Vec::new(),
 
             current_module: graph_root,
             ribs: PerNS {

src/librustc_resolve/resolve_imports.rs

@@ -635,7 +635,7 @@ impl<'a> Resolver<'a> {
 /// An error that may be transformed into a diagnostic later. Used to combine multiple unresolved
 /// import errors within the same use tree into a single diagnostic.
 #[derive(Debug, Clone)]
-struct UnresolvedImportError {
+pub struct UnresolvedImportError {
     span: Span,
     label: Option<String>,
     note: Vec<String>,
@@ -744,19 +744,23 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
         // to avoid generating multiple errors on the same import.
         if !has_errors {
             for import in &self.indeterminate_imports {
-                self.throw_unresolved_import_error(errors, Some(MultiSpan::from(import.span)));
+                let sp = Some(MultiSpan::from(import.span));
+                self.throw_unresolved_import_error(errors, sp);
                 break;
             }
         }
     }
 
     fn throw_unresolved_import_error(
-        &self,
+        &mut self,
         errors: Vec<(String, UnresolvedImportError)>,
         span: Option<MultiSpan>,
     ) {
         /// Upper limit on the number of `span_label` messages.
         const MAX_LABEL_COUNT: usize = 10;
+        for (_, error) in &errors {
+            self.unresolved_imports.push(error.span);
+        }
 
         let (span, msg) = if errors.is_empty() {
             (span.unwrap(), "unresolved import".to_string())

src/test/ui/imports/failed-imports.rs

@@ -0,0 +1,12 @@
+#![deny(unused_imports)]
+// there should be *no* unused import errors
+
+mod qux {
+   pub(in crate::qux) fn quz() {}
+}
+
+use qux::quz;//~ ERROR function `quz` is private
+use qux::bar;//~ ERROR unresolved import `qux::bar`
+use foo::bar; //~ ERROR unresolved import `foo`
+
+fn main() {}

src/test/ui/imports/failed-imports.stderr

@@ -0,0 +1,22 @@
+error[E0432]: unresolved import `qux::bar`
+  --> $DIR/failed-imports.rs:9:5
+   |
+LL | use qux::bar;
+   |     ^^^^^^^^ no `bar` in `qux`
+
+error[E0432]: unresolved import `foo`
+  --> $DIR/failed-imports.rs:10:5
+   |
+LL | use foo::bar;
+   |     ^^^ maybe a missing `extern crate foo;`?
+
+error[E0603]: function `quz` is private
+  --> $DIR/failed-imports.rs:8:10
+   |
+LL | use qux::quz;
+   |          ^^^
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0432, E0603.
+For more information about an error, try `rustc --explain E0432`.