Add a IsIdentity extension trait for CanonicalUserType

Author: compiler-errors

Diff for: Cargo.lock

@@ -370,9 +370,9 @@ checksum = "a3e2c3daef883ecc1b5d58c15adae93470a91d425f3532ba1695849656af3fc1"
 
 [[package]]
 name = "bytecount"
-version = "0.6.4"
+version = "0.6.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ad152d03a2c813c80bb94fedbf3a3f02b28f793e39e7c214c8a0bcc196343de7"
+checksum = "d1a12477b7237a01c11a80a51278165f9ba0edd28fa6db00a65ab230320dc58c"
 dependencies = [
  "packed_simd",
 ]
@@ -1673,9 +1673,9 @@ checksum = "8a9ee70c43aaf417c914396645a0fa852624801b24ebb7ae78fe8272889ac888"
 
 [[package]]
 name = "hashbrown"
-version = "0.14.2"
+version = "0.14.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f93e7192158dbcda357bdec5fb5788eebf8bbac027f3f33e719d29135ae84156"
+checksum = "2c6201b9ff9fd90a5a3bac2e56a830d0caa509576f0e503818ee82c181b3437a"
 dependencies = [
  "ahash",
  "allocator-api2",
@@ -1992,7 +1992,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d5477fe2230a79769d8dc68e0eabf5437907c0457a5614a9e8dddb67f65eb65d"
 dependencies = [
  "equivalent",
- "hashbrown 0.14.2",
+ "hashbrown 0.14.0",
  "rustc-rayon",
  "serde",
 ]
@@ -2626,7 +2626,7 @@ dependencies = [
  "compiler_builtins",
  "crc32fast",
  "flate2",
- "hashbrown 0.14.2",
+ "hashbrown 0.14.0",
  "indexmap 2.0.0",
  "memchr",
  "rustc-std-workspace-alloc",
@@ -5101,7 +5101,7 @@ dependencies = [
  "core",
  "dlmalloc",
  "fortanix-sgx-abi",
- "hashbrown 0.14.2",
+ "hashbrown 0.14.0",
  "hermit-abi 0.3.2",
  "libc",
  "miniz_oxide",
@@ -5421,7 +5421,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4db52ee8fec06e119b692ef3dd2c4cf621a99204c1b8c47407870ed050305b9b"
 dependencies = [
  "gimli",
- "hashbrown 0.14.2",
+ "hashbrown 0.14.0",
  "object",
  "tracing",
 ]

Diff for: compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -26,7 +26,7 @@ use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::visit::{TypeVisitable, TypeVisitableExt};
 use rustc_middle::ty::{
-    self, AdtKind, CanonicalUserType, GenericParamDefKind, Ty, TyCtxt, UserType,
+    self, AdtKind, CanonicalUserType, GenericParamDefKind, IsIdentity, Ty, TyCtxt, UserType,
 };
 use rustc_middle::ty::{GenericArgKind, GenericArgsRef, UserArgs, UserSelfTy};
 use rustc_session::lint;
@@ -208,7 +208,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         debug!("fcx {}", self.tag());
 
         // FIXME: is_identity being on `UserType` and not `Canonical<UserType>` is awkward
-        if !canonical_user_type_annotation.value.is_identity() {
+        if !canonical_user_type_annotation.is_identity() {
             self.typeck_results
                 .borrow_mut()
                 .user_provided_types_mut()

Diff for: compiler/rustc_middle/src/ty/mod.rs

@@ -106,8 +106,8 @@ pub use self::sty::{
 };
 pub use self::trait_def::TraitDef;
 pub use self::typeck_results::{
-    CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, TypeckResults,
-    UserType, UserTypeAnnotationIndex,
+    CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, IsIdentity,
+    TypeckResults, UserType, UserTypeAnnotationIndex,
 };
 
 pub mod _match;

Diff for: compiler/rustc_middle/src/ty/typeck_results.rs

@@ -607,11 +607,15 @@ pub enum UserType<'tcx> {
     TypeOf(DefId, UserArgs<'tcx>),
 }
 
-impl<'tcx> UserType<'tcx> {
+pub trait IsIdentity {
+    fn is_identity(&self) -> bool;
+}
+
+impl<'tcx> IsIdentity for CanonicalUserType<'tcx> {
     /// Returns `true` if this represents a substitution of the form `[?0, ?1, ?2]`,
     /// i.e., each thing is mapped to a canonical variable with the same index.
-    pub fn is_identity(&self) -> bool {
-        match self {
+    fn is_identity(&self) -> bool {
+        match self.value {
             UserType::Ty(_) => false,
             UserType::TypeOf(_, user_args) => {
                 if user_args.user_self_ty.is_some() {