Add generic arg infer

compiler/rustc_middle/src/hir/map/collector.rs

@@ -404,6 +404,14 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
         });
     }
 
+    fn visit_infer(&mut self, inf: &'hir InferArg) {
+        self.insert(inf.span, inf.hir_id, Node::Infer(inf));
+
+        self.with_parent(inf.hir_id, |this| {
+            intravisit::walk_inf(this, inf);
+        });
+    }
+
     fn visit_trait_ref(&mut self, tr: &'hir TraitRef<'hir>) {
         self.insert(tr.path.span, tr.hir_ref_id, Node::TraitRef(tr));
 

compiler/rustc_middle/src/hir/map/mod.rs

@@ -272,6 +272,7 @@ impl<'hir> Map<'hir> {
                 GenericParamKind::Type { .. } => DefKind::TyParam,
                 GenericParamKind::Const { .. } => DefKind::ConstParam,
             },
+            Node::Infer(_) => todo!(),
             Node::Crate(_) => DefKind::Mod,
             Node::Stmt(_)
             | Node::PathSegment(_)
@@ -882,6 +883,7 @@ impl<'hir> Map<'hir> {
                 node: VisibilityKind::Restricted { ref path, .. },
                 ..
             }) => path.span,
+            Node::Infer(i) => i.span,
             Node::Visibility(v) => bug!("unexpected Visibility {:?}", v),
             Node::Local(local) => local.span,
             Node::MacroDef(macro_def) => macro_def.span,
@@ -1129,6 +1131,7 @@ fn hir_id_to_string(map: &Map<'_>, id: HirId) -> String {
         Some(Node::Param(_)) => node_str("param"),
         Some(Node::Arm(_)) => node_str("arm"),
         Some(Node::Block(_)) => node_str("block"),
+        Some(Node::Infer(_)) => node_str("infer"),
         Some(Node::Local(_)) => node_str("local"),
         Some(Node::Ctor(..)) => format!("ctor {}{}", path_str(), id_str),
         Some(Node::Lifetime(_)) => node_str("lifetime"),