Fix redundant import errors for preload extern crate

Author: chenyukang

compiler/rustc_lint/src/context/diagnostics.rs

@@ -103,11 +103,21 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
                 );
             }
         }
-        BuiltinLintDiag::RedundantImport(spans, ident) => {
+        BuiltinLintDiag::RedundantImport(spans, ident, import_span) => {
             for (span, is_imported) in spans {
                 let introduced = if is_imported { "imported" } else { "defined" };
-                diag.span_label(span, format!("the item `{ident}` is already {introduced} here"));
+                let span_msg = if span.is_dummy() { "by prelude" } else { "here" };
+                diag.span_label(
+                    span,
+                    format!("the item `{ident}` is already {introduced} {span_msg}"),
+                );
             }
+            diag.span_suggestion(
+                import_span,
+                "remove this import",
+                "",
+                Applicability::MachineApplicable,
+            );
         }
         BuiltinLintDiag::DeprecatedMacro(suggestion, span) => {
             stability::deprecation_suggestion(diag, "macro", suggestion, span)

compiler/rustc_lint_defs/src/lib.rs

@@ -577,7 +577,7 @@ pub enum BuiltinLintDiag {
     ElidedLifetimesInPaths(usize, Span, bool, Span),
     UnknownCrateTypes(Span, String, String),
     UnusedImports(String, Vec<(Span, String)>, Option<Span>),
-    RedundantImport(Vec<(Span, bool)>, Ident),
+    RedundantImport(Vec<(Span, bool)>, Ident, Span),
     DeprecatedMacro(Option<Symbol>, Span),
     MissingAbi(Span, Abi),
     UnusedDocComment(Span),

compiler/rustc_resolve/src/imports.rs

@@ -1334,9 +1334,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         }
 
         let mut is_redundant = true;
-
         let mut redundant_span = PerNS { value_ns: None, type_ns: None, macro_ns: None };
-
         self.per_ns(|this, ns| {
             if is_redundant && let Ok(binding) = source_bindings[ns].get() {
                 if binding.res() == Res::Err {
@@ -1373,7 +1371,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 id,
                 import.span,
                 format!("the item `{source}` is imported redundantly"),
-                BuiltinLintDiag::RedundantImport(redundant_spans, source),
+                BuiltinLintDiag::RedundantImport(redundant_spans, source, import.use_span),
             );
         }
     }

tests/ui/imports/auxiliary/aux-issue-121915.rs

@@ -0,0 +1 @@
+pub fn item() {}

tests/ui/imports/redundant-import-issue-121915-2015.rs

@@ -0,0 +1,11 @@
+//@ compile-flags: --extern aux_issue_121915 --edition 2015
+//@ aux-build: aux-issue-121915.rs
+
+extern crate aux_issue_121915;
+
+#[deny(unused_imports)]
+fn main() {
+    use aux_issue_121915;
+    //~^ ERROR the item `aux_issue_121915` is imported redundantly
+    aux_issue_121915::item();
+}

tests/ui/imports/redundant-import-issue-121915-2015.stderr

@@ -0,0 +1,17 @@
+error: the item `aux_issue_121915` is imported redundantly
+  --> $DIR/redundant-import-issue-121915-2015.rs:8:9
+   |
+LL | extern crate aux_issue_121915;
+   | ------------------------------ the item `aux_issue_121915` is already imported here
+...
+LL |     use aux_issue_121915;
+   |     ----^^^^^^^^^^^^^^^^- help: remove this import
+   |
+note: the lint level is defined here
+  --> $DIR/redundant-import-issue-121915-2015.rs:6:8
+   |
+LL | #[deny(unused_imports)]
+   |        ^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/imports/redundant-import-issue-121915.rs

@@ -0,0 +1,9 @@
+//@ compile-flags: --extern aux_issue_121915 --edition 2018
+//@ aux-build: aux-issue-121915.rs
+
+#[deny(unused_imports)]
+fn main() {
+    use aux_issue_121915;
+    //~^ ERROR the item `aux_issue_121915` is imported redundantly
+    aux_issue_121915::item();
+}

tests/ui/imports/redundant-import-issue-121915.stderr

@@ -0,0 +1,17 @@
+error: the item `aux_issue_121915` is imported redundantly
+  --> $DIR/redundant-import-issue-121915.rs:6:9
+   |
+LL |     use aux_issue_121915;
+   |     ----^^^^^^^^^^^^^^^^-
+   |     |   |
+   |     |   the item `aux_issue_121915` is already defined by prelude
+   |     help: remove this import
+   |
+note: the lint level is defined here
+  --> $DIR/redundant-import-issue-121915.rs:4:8
+   |
+LL | #[deny(unused_imports)]
+   |        ^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/imports/suggest-remove-issue-121315.fixed

@@ -0,0 +1,8 @@
+//@ run-rustfix
+//@ compile-flags: --edition 2021
+#[deny(unused_imports)]
+//~^ ERROR the item `TryFrom` is imported redundantly
+
+fn main() {
+    let _ = u32::try_from(5i32);
+}

tests/ui/imports/suggest-remove-issue-121315.rs

@@ -0,0 +1,9 @@
+//@ run-rustfix
+//@ compile-flags: --edition 2021
+#[deny(unused_imports)]
+use std::convert::TryFrom;
+//~^ ERROR the item `TryFrom` is imported redundantly
+
+fn main() {
+    let _ = u32::try_from(5i32);
+}