Inline fn get_fn_sig into its callers.

cc_bindings_from_rs/generate_bindings/BUILD

@@ -58,6 +58,7 @@ crubit_rust_test(
     rustc_flags = ["-Zallow-features=rustc_private"],
     deps = [
         ":generate_bindings",
+        ":query_compiler",
         ":test_helpers",
         "//cc_bindings_from_rs:run_compiler_test_support",
         "//cc_bindings_from_rs/generate_bindings/database",

cc_bindings_from_rs/generate_bindings/format_type_test.rs

@@ -6,8 +6,8 @@
 
 use code_gen_utils::format_cc_includes;
 use database::TypeLocation;
-use generate_bindings::generate_function::get_fn_sig;
 use proc_macro2::TokenStream;
+use query_compiler::liberate_and_deanonymize_late_bound_regions;
 use quote::quote;
 use run_compiler_test_support::{find_def_id_by_name, run_compiler_for_testing};
 use rustc_middle::ty::{Ty, TyCtxt};
@@ -41,7 +41,14 @@ fn test_ty<TestFn, Expectation>(
     }
 
     fn get_test_function_ty<'tcx>(tcx: TyCtxt<'tcx>, type_location: TypeLocation) -> Ty<'tcx> {
-        let sig_mid = get_fn_sig(tcx, find_def_id_by_name(tcx, "test_function").to_def_id());
+        let sig_mid = {
+            let def_id = find_def_id_by_name(tcx, "test_function").to_def_id();
+            liberate_and_deanonymize_late_bound_regions(
+                tcx,
+                tcx.fn_sig(def_id).instantiate_identity(),
+                def_id,
+            )
+        };
         match type_location {
             TypeLocation::FnReturn { .. } => sig_mid.output(),
             TypeLocation::FnParam { .. } => sig_mid.inputs()[0],

cc_bindings_from_rs/generate_bindings/generate_function.rs

@@ -675,7 +675,11 @@ pub(crate) fn generate_thunk_call<'tcx>(
 pub(crate) fn fn_arg_idents(tcx: TyCtxt, def_id: DefId) -> Vec<Option<rustc_span::Ident>> {
     match tcx.def_kind(def_id) {
         DefKind::Ctor { .. } => {
-            vec![None; get_fn_sig(tcx, def_id).inputs().len()]
+            // Documentation of `skip_binder` says that accessing generic args in the returned value
+            // is generally incorrect, but specifically points out that it should be okay to use
+            // it to get the number of arguments of an `FnSig`.
+            let arg_count = tcx.fn_sig(def_id).skip_binder().inputs().skip_binder().len();
+            vec![None; arg_count]
         }
         _ => tcx.fn_arg_idents(def_id).iter().cloned().collect_vec(),
     }
@@ -751,12 +755,17 @@ pub fn generate_function<'tcx>(
     def_id: DefId,
 ) -> Result<ApiSnippets<'tcx>> {
     let tcx = db.tcx();
+
+    // TODO(b/281542952): Add support for `impl Into<T>` => `T` and similar substitutions.
     ensure!(
         !tcx.generics_of(def_id).requires_monomorphization(tcx),
         "Generic functions are not supported yet (b/259749023)"
     );
-
-    let sig_mid = get_fn_sig(tcx, def_id);
+    let sig_mid = liberate_and_deanonymize_late_bound_regions(
+        tcx,
+        tcx.fn_sig(def_id).instantiate_identity(),
+        def_id,
+    );
     check_fn_sig(&sig_mid)?;
 
     let trait_ref = tcx
@@ -1076,18 +1085,3 @@ pub fn check_fn_sig(sig: &ty::FnSig) -> Result<()> {
 
     Ok(())
 }
-
-/// Returns the rustc_middle and rustc_hir function signatures.
-///
-/// In the case of rustc_hir, this returns the `FnDecl`, not the
-/// `rustc_hir::FnSig`, because the `FnDecl` type is used for both function
-/// pointers and actual functions. This makes it a more useful vocabulary type.
-/// `FnDecl` does drop information, but that information is already on the
-/// rustc_middle `FnSig`, so there is no loss.
-pub fn get_fn_sig<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> ty::FnSig<'tcx> {
-    liberate_and_deanonymize_late_bound_regions(
-        tcx,
-        tcx.fn_sig(def_id).instantiate_identity(),
-        def_id,
-    )
-}