Filter out intrinsics if we have other import candidates to suggest

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -384,7 +384,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 
         // Try to lookup name in more relaxed fashion for better error reporting.
         let ident = path.last().unwrap().ident;
-        let candidates = self
+        let mut candidates = self
             .r
             .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
             .into_iter()
@@ -396,6 +396,18 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
             })
             .collect::<Vec<_>>();
         let crate_def_id = CRATE_DEF_ID.to_def_id();
+        // Try to filter out intrinsics candidates, as long as we have
+        // some other candidates to suggest.
+        let intrinsic_candidates: Vec<_> = candidates
+            .drain_filter(|sugg| {
+                let path = path_names_to_string(&sugg.path);
+                path.starts_with("core::intrinsics::") || path.starts_with("std::intrinsics::")
+            })
+            .collect();
+        if candidates.is_empty() {
+            // Put them back if we have no more candidates to suggest...
+            candidates.extend(intrinsic_candidates);
+        }
         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
             let mut enum_candidates: Vec<_> = self
                 .r

src/test/ui/resolve/filter-intrinsics.rs

@@ -0,0 +1,10 @@
+fn main() {
+    // Should suggest only `std::mem::size_of`
+    let _ = size_of::<usize>();
+    //~^ ERROR cannot find
+
+    // Should suggest `std::intrinsics::fabsf64`,
+    // since there is no non-intrinsic to suggest.
+    let _ = fabsf64(1.0);
+    //~^ ERROR cannot find
+}

src/test/ui/resolve/filter-intrinsics.stderr

@@ -0,0 +1,25 @@
+error[E0425]: cannot find function `size_of` in this scope
+  --> $DIR/filter-intrinsics.rs:3:13
+   |
+LL |     let _ = size_of::<usize>();
+   |             ^^^^^^^ not found in this scope
+   |
+help: consider importing this function
+   |
+LL | use std::mem::size_of;
+   |
+
+error[E0425]: cannot find function `fabsf64` in this scope
+  --> $DIR/filter-intrinsics.rs:8:13
+   |
+LL |     let _ = fabsf64(1.0);
+   |             ^^^^^^^ not found in this scope
+   |
+help: consider importing this function
+   |
+LL | use std::intrinsics::fabsf64;
+   |
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0425`.