Fix types being marked as dead when they are inferred generic arguments

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

Author: JonathanBrouwer

compiler/rustc_passes/src/dead.rs

@@ -125,9 +125,13 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
  ) => {
  self.check_def_id(def_id);
  }
- _ if self.in_pat => {}
  Res::PrimTy(..) | Res::SelfCtor(..) | Res::Local(..) => {}
  Res::Def(DefKind::Ctor(CtorOf::Variant, ..), ctor_def_id) => {
+ // Using a variant in patterns should not make the variant live,
+ // since we can just remove the match arm that matches the pattern
+ if self.in_pat {
+ return;
+ }
  let variant_id = self.tcx.parent(ctor_def_id);
  let enum_id = self.tcx.parent(variant_id);
  self.check_def_id(enum_id);
@@ -136,6 +140,11 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
  }
  }
  Res::Def(DefKind::Variant, variant_id) => {
+ // Using a variant in patterns should not make the variant live,
+ // since we can just remove the match arm that matches the pattern
+ if self.in_pat {
+ return;
+ }
  let enum_id = self.tcx.parent(variant_id);
  self.check_def_id(enum_id);
  if !self.ignore_variant_stack.contains(&variant_id) {

tests/ui/lint/dead-code/inferred-generic-arg.rs

@@ -0,0 +1,19 @@
+//@ check-pass
+
+#![deny(dead_code)]
+
+#[derive(Default)]
+struct Test {
+
+}
+
+fn main() {
+ if let Some::<Test>(test) = magic::<Test>() {
+
+ }
+}
+
+
+fn magic<T: Default>() -> Option<T> {
+ Some(T::default())
+}