Add a dep kind for use of the anon node with zero dependencies

compiler/rustc_middle/src/dep_graph/dep_node.rs

@@ -89,6 +89,7 @@ rustc_query_append!(define_dep_nodes![
     /// We use this to create a forever-red node.
     [] fn Red() -> (),
     [] fn SideEffect() -> (),
+    [] fn AnonZeroDeps() -> (),
     [] fn TraitSelect() -> (),
     [] fn CompileCodegenUnit() -> (),
     [] fn CompileMonoItem() -> (),

compiler/rustc_middle/src/dep_graph/mod.rs

@@ -53,6 +53,7 @@ impl Deps for DepsType {
     const DEP_KIND_NULL: DepKind = dep_kinds::Null;
     const DEP_KIND_RED: DepKind = dep_kinds::Red;
     const DEP_KIND_SIDE_EFFECT: DepKind = dep_kinds::SideEffect;
+    const DEP_KIND_ANON_ZERO_DEPS: DepKind = dep_kinds::AnonZeroDeps;
     const DEP_KIND_MAX: u16 = dep_node::DEP_KIND_VARIANTS - 1;
 }
 

compiler/rustc_query_impl/src/plumbing.rs

@@ -870,6 +870,17 @@ macro_rules! define_queries {
                 }
             }
 
+            pub(crate) fn AnonZeroDeps<'tcx>() -> DepKindStruct<'tcx> {
+                DepKindStruct {
+                    is_anon: true,
+                    is_eval_always: false,
+                    fingerprint_style: FingerprintStyle::Opaque,
+                    force_from_dep_node: Some(|_, _, _| bug!("cannot force an anon node")),
+                    try_load_from_on_disk_cache: None,
+                    name: &"AnonZeroDeps",
+                }
+            }
+
             pub(crate) fn TraitSelect<'tcx>() -> DepKindStruct<'tcx> {
                 DepKindStruct {
                     is_anon: true,

compiler/rustc_query_system/src/dep_graph/graph.rs

@@ -50,7 +50,7 @@ rustc_index::newtype_index! {
 rustc_data_structures::static_assert_size!(Option<DepNodeIndex>, 4);
 
 impl DepNodeIndex {
-    const SINGLETON_DEPENDENCYLESS_ANON_NODE: DepNodeIndex = DepNodeIndex::ZERO;
+    const SINGLETON_ZERO_DEPS_ANON_NODE: DepNodeIndex = DepNodeIndex::ZERO;
     pub const FOREVER_RED_NODE: DepNodeIndex = DepNodeIndex::from_u32(1);
 }
 
@@ -140,13 +140,13 @@ impl<D: Deps> DepGraph<D> {
 
         let colors = DepNodeColorMap::new(prev_graph_node_count);
 
-        // Instantiate a dependy-less node only once for anonymous queries.
+        // Instantiate a node with zero dependencies only once for anonymous queries.
         let _green_node_index = current.alloc_node(
-            DepNode { kind: D::DEP_KIND_NULL, hash: current.anon_id_seed.into() },
+            DepNode { kind: D::DEP_KIND_ANON_ZERO_DEPS, hash: current.anon_id_seed.into() },
             EdgesVec::new(),
             Fingerprint::ZERO,
         );
-        assert_eq!(_green_node_index, DepNodeIndex::SINGLETON_DEPENDENCYLESS_ANON_NODE);
+        assert_eq!(_green_node_index, DepNodeIndex::SINGLETON_ZERO_DEPS_ANON_NODE);
 
         // Instantiate a dependy-less red node only once for anonymous queries.
         let red_node_index = current.alloc_node(
@@ -407,7 +407,7 @@ impl<D: Deps> DepGraphData<D> {
                 // going to be (i.e. equal to the precomputed
                 // `SINGLETON_DEPENDENCYLESS_ANON_NODE`). As a consequence we can skip creating
                 // a `StableHasher` and sending the node through interning.
-                DepNodeIndex::SINGLETON_DEPENDENCYLESS_ANON_NODE
+                DepNodeIndex::SINGLETON_ZERO_DEPS_ANON_NODE
             }
             1 => {
                 // When there is only one dependency, don't bother creating a node.

compiler/rustc_query_system/src/dep_graph/mod.rs

@@ -111,6 +111,9 @@ pub trait Deps {
     /// We use this to create a side effect node.
     const DEP_KIND_SIDE_EFFECT: DepKind;
 
+    /// We use this to create the anon node with zero dependencies.
+    const DEP_KIND_ANON_ZERO_DEPS: DepKind;
+
     /// This is the highest value a `DepKind` can have. It's used during encoding to
     /// pack information into the unused bits.
     const DEP_KIND_MAX: u16;