Add generic arg infer

compiler/rustc_hir/src/hir.rs

@@ -253,11 +253,24 @@ pub struct ConstArg {
     pub span: Span,
 }
 
+#[derive(Encodable, Debug, HashStable_Generic)]
+pub struct InferArg {
+    pub hir_id: HirId,
+    pub span: Span,
+}
+
+impl InferArg {
+    pub fn to_ty(&self) -> Ty<'_> {
+        Ty { kind: TyKind::Infer, span: self.span, hir_id: self.hir_id }
+    }
+}
+
 #[derive(Debug, HashStable_Generic)]
 pub enum GenericArg<'hir> {
     Lifetime(Lifetime),
     Type(Ty<'hir>),
     Const(ConstArg),
+    Infer(InferArg),
 }
 
 impl GenericArg<'_> {
@@ -266,6 +279,7 @@ impl GenericArg<'_> {
             GenericArg::Lifetime(l) => l.span,
             GenericArg::Type(t) => t.span,
             GenericArg::Const(c) => c.span,
+            GenericArg::Infer(i) => i.span,
         }
     }
 
@@ -274,6 +288,7 @@ impl GenericArg<'_> {
             GenericArg::Lifetime(l) => l.hir_id,
             GenericArg::Type(t) => t.hir_id,
             GenericArg::Const(c) => c.value.hir_id,
+            GenericArg::Infer(i) => i.hir_id,
         }
     }
 
@@ -290,6 +305,7 @@ impl GenericArg<'_> {
             GenericArg::Lifetime(_) => "lifetime",
             GenericArg::Type(_) => "type",
             GenericArg::Const(_) => "constant",
+            GenericArg::Infer(_) => "inferred",
         }
     }
 
@@ -300,6 +316,7 @@ impl GenericArg<'_> {
             GenericArg::Const(_) => {
                 ast::ParamKindOrd::Const { unordered: feats.unordered_const_ty_params() }
             }
+            GenericArg::Infer(_) => ast::ParamKindOrd::Infer,
         }
     }
 }
@@ -341,6 +358,7 @@ impl GenericArgs<'_> {
                         break;
                     }
                     GenericArg::Const(_) => {}
+                    GenericArg::Infer(_) => {}
                 }
             }
         }
@@ -358,6 +376,7 @@ impl GenericArgs<'_> {
                 GenericArg::Lifetime(_) => own_counts.lifetimes += 1,
                 GenericArg::Type(_) => own_counts.types += 1,
                 GenericArg::Const(_) => own_counts.consts += 1,
+                GenericArg::Infer(_) => own_counts.infer += 1,
             };
         }
 
@@ -484,6 +503,7 @@ pub struct GenericParamCount {
     pub lifetimes: usize,
     pub types: usize,
     pub consts: usize,
+    pub infer: usize,
 }
 
 /// Represents lifetimes and type parameters attached to a declaration
@@ -2987,6 +3007,8 @@ pub enum Node<'hir> {
     Visibility(&'hir Visibility<'hir>),
 
     Crate(&'hir Mod<'hir>),
+
+    Infer(&'hir InferArg),
 }
 
 impl<'hir> Node<'hir> {
@@ -3055,6 +3077,7 @@ impl<'hir> Node<'hir> {
             | Node::Local(Local { hir_id, .. })
             | Node::Lifetime(Lifetime { hir_id, .. })
             | Node::Param(Param { hir_id, .. })
+            | Node::Infer(InferArg { hir_id, .. })
             | Node::GenericParam(GenericParam { hir_id, .. }) => Some(*hir_id),
             Node::TraitRef(TraitRef { hir_ref_id, .. }) => Some(*hir_ref_id),
             Node::PathSegment(PathSegment { hir_id, .. }) => *hir_id,