Use `IntoIterator` for `mk_fn_sig`.

This makes a lot of call sites nicer.

11 files changed, 28 insertions, 35 deletions

diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
index ace15cfb024..3dc0ac03312 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
@@ -27,8 +27,6 @@ use rustc_middle::ty::Instance;
 use std::cell::RefCell;
 use std::ffi::CString;
 
-use std::iter;
-
 pub mod mapgen;
 
 const UNUSED_FUNCTION_COUNTER_ID: CounterValueReference = CounterValueReference::START;
@@ -201,7 +199,7 @@ fn declare_unused_fn<'tcx>(cx: &CodegenCx<'_, 'tcx>, def_id: DefId) -> Instance<
         tcx.symbol_name(instance).name,
         cx.fn_abi_of_fn_ptr(
             ty::Binder::dummy(tcx.mk_fn_sig(
-                iter::once(tcx.mk_unit()),
+                [tcx.mk_unit()],
                 tcx.mk_unit(),
                 false,
                 hir::Unsafety::Unsafe,
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index b0295481ca5..39afb4af6f6 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -22,7 +22,6 @@ use rustc_target::abi::{self, Align, HasDataLayout, Primitive};
 use rustc_target::spec::{HasTargetSpec, PanicStrategy};
 
 use std::cmp::Ordering;
-use std::iter;
 
 fn get_simple_intrinsic<'ll>(
     cx: &CodegenCx<'ll, '_>,
@@ -798,7 +797,7 @@ fn get_rust_try_fn<'ll, 'tcx>(
     let i8p = tcx.mk_mut_ptr(tcx.types.i8);
     // `unsafe fn(*mut i8) -> ()`
     let try_fn_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
-        iter::once(i8p),
+        [i8p],
         tcx.mk_unit(),
         false,
         hir::Unsafety::Unsafe,
@@ -806,7 +805,7 @@ fn get_rust_try_fn<'ll, 'tcx>(
     )));
     // `unsafe fn(*mut i8, *mut i8) -> ()`
     let catch_fn_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
-        [i8p, i8p].iter().cloned(),
+        [i8p, i8p],
         tcx.mk_unit(),
         false,
         hir::Unsafety::Unsafe,
@@ -814,7 +813,7 @@ fn get_rust_try_fn<'ll, 'tcx>(
     )));
     // `unsafe fn(unsafe fn(*mut i8) -> (), *mut i8, unsafe fn(*mut i8, *mut i8) -> ()) -> i32`
     let rust_fn_sig = ty::Binder::dummy(cx.tcx.mk_fn_sig(
-        [try_fn_ty, i8p, catch_fn_ty].into_iter(),
+        [try_fn_ty, i8p, catch_fn_ty],
         tcx.types.i32,
         false,
         hir::Unsafety::Unsafe,
diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs
index 5bb78d17253..4cf15923793 100644
--- a/compiler/rustc_hir_analysis/src/astconv/mod.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs
@@ -3109,7 +3109,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         debug!(?output_ty);
 
-        let fn_ty = tcx.mk_fn_sig(input_tys.into_iter(), output_ty, decl.c_variadic, unsafety, abi);
+        let fn_ty = tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi);
         let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
 
         if !self.allow_ty_infer() && !(visitor.0.is_empty() && infer_replacements.is_empty()) {
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
index 51700cf846b..8d9d8fa5654 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
@@ -15,8 +15,6 @@ use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_target::spec::abi::Abi;
 
-use std::iter;
-
 fn equate_intrinsic_type<'tcx>(
     tcx: TyCtxt<'tcx>,
     it: &hir::ForeignItem<'_>,
@@ -385,14 +383,14 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
             kw::Try => {
                 let mut_u8 = tcx.mk_mut_ptr(tcx.types.u8);
                 let try_fn_ty = ty::Binder::dummy(tcx.mk_fn_sig(
-                    iter::once(mut_u8),
+                    [mut_u8],
                     tcx.mk_unit(),
                     false,
                     hir::Unsafety::Normal,
                     Abi::Rust,
                 ));
                 let catch_fn_ty = ty::Binder::dummy(tcx.mk_fn_sig(
-                    [mut_u8, mut_u8].iter().cloned(),
+                    [mut_u8, mut_u8],
                     tcx.mk_unit(),
                     false,
                     hir::Unsafety::Normal,
@@ -447,7 +445,7 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
         };
         (n_tps, 0, inputs, output, unsafety)
     };
-    let sig = tcx.mk_fn_sig(inputs.into_iter(), output, false, unsafety, Abi::RustIntrinsic);
+    let sig = tcx.mk_fn_sig(inputs, output, false, unsafety, Abi::RustIntrinsic);
     let sig = ty::Binder::bind_with_vars(sig, bound_vars);
     equate_intrinsic_type(tcx, it, n_tps, n_lts, sig)
 }
@@ -545,13 +543,7 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
         }
     };
 
-    let sig = tcx.mk_fn_sig(
-        inputs.into_iter(),
-        output,
-        false,
-        hir::Unsafety::Unsafe,
-        Abi::PlatformIntrinsic,
-    );
+    let sig = tcx.mk_fn_sig(inputs, output, false, hir::Unsafety::Unsafe, Abi::PlatformIntrinsic);
     let sig = ty::Binder::dummy(sig);
     equate_intrinsic_type(tcx, it, n_tps, 0, sig)
 }
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index 6111046a519..11240cf22e4 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -113,7 +113,6 @@ use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
 
-use std::iter;
 use std::ops::Not;
 
 use astconv::AstConv;
@@ -348,7 +347,7 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
     }
 
     let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
-        tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
+        tcx.mk_fn_sig([], expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
     }));
 
     require_same_types(
@@ -434,7 +433,7 @@ fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
             }
 
             let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
-                [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
+                [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))],
                 tcx.types.isize,
                 false,
                 hir::Unsafety::Normal,
diff --git a/compiler/rustc_hir_typeck/src/check.rs b/compiler/rustc_hir_typeck/src/check.rs
index 2b3678d9875..bf8259ff70f 100644
--- a/compiler/rustc_hir_typeck/src/check.rs
+++ b/compiler/rustc_hir_typeck/src/check.rs
@@ -264,7 +264,7 @@ fn check_lang_start_fn<'tcx>(
         let fn_generic = generics.param_at(0, tcx);
         let generic_ty = tcx.mk_ty_param(fn_generic.index, fn_generic.name);
         let expected_fn_sig =
-            tcx.mk_fn_sig([].into_iter(), generic_ty, false, hir::Unsafety::Normal, Abi::Rust);
+            tcx.mk_fn_sig([], generic_ty, false, hir::Unsafety::Normal, Abi::Rust);
         let expected_ty = tcx.mk_fn_ptr(Binder::dummy(expected_fn_sig));
 
         // we emit the same error to suggest changing the arg no matter what's wrong with the arg
diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
index b1268c5f792..cf296a7bf65 100644
--- a/compiler/rustc_hir_typeck/src/closure.rs
+++ b/compiler/rustc_hir_typeck/src/closure.rs
@@ -126,7 +126,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // the `closures` table.
         let sig = bound_sig.map_bound(|sig| {
             self.tcx.mk_fn_sig(
-                iter::once(self.tcx.intern_tup(sig.inputs())),
+                [self.tcx.intern_tup(sig.inputs())],
                 sig.output(),
                 sig.c_variadic,
                 sig.unsafety,
@@ -326,7 +326,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         debug!(?ret_param_ty);
 
         let sig = projection.rebind(self.tcx.mk_fn_sig(
-            input_tys.iter(),
+            input_tys,
             ret_param_ty,
             false,
             hir::Unsafety::Normal,
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 7b4434a3843..e1a72c70145 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -1660,11 +1660,11 @@ impl<'tcx> TyCtxt<'tcx> {
         unsafety: hir::Unsafety,
     ) -> PolyFnSig<'tcx> {
         sig.map_bound(|s| {
-            let params_iter = match s.inputs()[0].kind() {
-                ty::Tuple(params) => params.into_iter(),
+            let params = match s.inputs()[0].kind() {
+                ty::Tuple(params) => *params,
                 _ => bug!(),
             };
-            self.mk_fn_sig(params_iter, s.output(), s.c_variadic, unsafety, abi::Abi::Rust)
+            self.mk_fn_sig(params, s.output(), s.c_variadic, unsafety, abi::Abi::Rust)
         })
     }
 
@@ -2215,6 +2215,11 @@ impl<'tcx> TyCtxt<'tcx> {
         if ts.is_empty() { List::empty() } else { self._intern_bound_variable_kinds(ts) }
     }
 
+    // Unlike various other `mk_*` functions, this one uses `I: IntoIterator`
+    // instead of `I: Iterator`. Unlike those other functions, this one doesn't
+    // have a `intern_fn_sig` variant that can be used for cases where `I` is
+    // something like a `Vec`. That's because of the need to combine `inputs`
+    // and `output`.
     pub fn mk_fn_sig<I, T>(
         self,
         inputs: I,
@@ -2224,10 +2229,10 @@ impl<'tcx> TyCtxt<'tcx> {
         abi: abi::Abi,
     ) -> T::Output
     where
-        I: Iterator<Item = T>,
+        I: IntoIterator<Item = T>,
         T: CollectAndApply<Ty<'tcx>, ty::FnSig<'tcx>>,
     {
-        T::collect_and_apply(inputs.chain(iter::once(output)), |xs| ty::FnSig {
+        T::collect_and_apply(inputs.into_iter().chain(iter::once(output)), |xs| ty::FnSig {
             inputs_and_output: self.intern_type_list(xs),
             c_variadic,
             unsafety,
diff --git a/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs b/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
index c2eccbcbc3c..59a2227cd36 100644
--- a/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
+++ b/compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
@@ -781,7 +781,7 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
                 let output = transform_ty(tcx, fn_sig.skip_binder().output(), options);
                 ty = tcx.mk_fn_ptr(ty::Binder::bind_with_vars(
                     tcx.mk_fn_sig(
-                        parameters.into_iter(),
+                        parameters,
                         output,
                         fn_sig.c_variadic(),
                         fn_sig.unsafety(),
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index a0c67f480d0..91b463800a8 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -2012,7 +2012,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             let sig = match inputs.kind() {
                 ty::Tuple(inputs) if infcx.tcx.is_fn_trait(trait_ref.def_id()) => {
                     infcx.tcx.mk_fn_sig(
-                        inputs.iter(),
+                        *inputs,
                         infcx.next_ty_var(TypeVariableOrigin {
                             span: DUMMY_SP,
                             kind: TypeVariableOriginKind::MiscVariable,
@@ -2023,7 +2023,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     )
                 }
                 _ => infcx.tcx.mk_fn_sig(
-                    std::iter::once(inputs),
+                    [inputs],
                     infcx.next_ty_var(TypeVariableOrigin {
                         span: DUMMY_SP,
                         kind: TypeVariableOriginKind::MiscVariable,
diff --git a/compiler/rustc_ty_utils/src/abi.rs b/compiler/rustc_ty_utils/src/abi.rs
index 76ecb86efb8..41924dc2a6d 100644
--- a/compiler/rustc_ty_utils/src/abi.rs
+++ b/compiler/rustc_ty_utils/src/abi.rs
@@ -141,7 +141,7 @@ fn fn_sig_for_fn_abi<'tcx>(
 
             ty::Binder::bind_with_vars(
                 tcx.mk_fn_sig(
-                    [env_ty, resume_ty].into_iter(),
+                    [env_ty, resume_ty],
                     ret_ty,
                     false,
                     hir::Unsafety::Normal,