[PATCH] libstdc++: Fix various bugs in ranges_algo.h [PR100187, ...]

[Patrick Palka]

This fixes some bugs with our ranges algorithms in uncommon situations,
such as when the return type of a predicate is a non-copyable class type
that's implicitly convertible to bool (PR100187), when a comparison
predicate isn't invocable as an rvalue (PR100237), and when the return
type of a projection function is non-copyable (PR100249).

This also fixes PR100287, which reports that we're moving __first twice
when constructing an empty subrange with it in ranges::partition.

Tested on x86_64-pc-linux-gnu, does this look OK for trunk and perhaps
the releases branches?  I wasn't sure if it's worthwhile to include
tests for these bugs given their relatively obscure nature.

libstdc++-v3/ChangeLog:

	PR libstdc++/100187
	PR libstdc++/100237
	PR libstdc++/100249
	PR libstdc++/100287
	* include/bits/ranges_algo.h (__search_n_fn::operator()): Give
	__value_comp lambda an explicit bool return type.
	(__is_permutation_fn::operator()): Give __proj_scan local
	variable auto&& return type.  Give __comp_scan lambda an
	explicit bool return type.
	(__remove_fn::operator()): Give __pred lambda an explicit
	bool return type.
	(__partition_fn::operator()): Don't std::move __first twice
	when returning an empty range.
	(__min_fn::operator()): Don't std::move __comp.
	(__max_fn::operator()): Likewise.
	(__minmax_fn::operator()): Likewise.
---
 libstdc++-v3/include/bits/ranges_algo.h | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index 23e6480b9a8..cda3042c11f 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -562,7 +562,7 @@ namespace ranges
 	if (__count <= 0)
 	  return {__first, __first};
 
-	auto __value_comp = [&] <typename _Rp> (_Rp&& __arg) {
+	auto __value_comp = [&] <typename _Rp> (_Rp&& __arg) -> bool {
 	    return std::__invoke(__pred, std::forward<_Rp>(__arg), __value);
 	};
 	if (__count == 1)
@@ -805,8 +805,8 @@ namespace ranges
 
 	for (auto __scan = __first1; __scan != __last1; ++__scan)
 	  {
-	    auto __proj_scan = std::__invoke(__proj1, *__scan);
-	    auto __comp_scan = [&] <typename _Tp> (_Tp&& __arg) {
+	    auto&& __proj_scan = std::__invoke(__proj1, *__scan);
+	    auto __comp_scan = [&] <typename _Tp> (_Tp&& __arg) -> bool {
 	      return std::__invoke(__pred, __proj_scan,
 				   std::forward<_Tp>(__arg));
 	    };
@@ -1256,7 +1256,7 @@ namespace ranges
       operator()(_Iter __first, _Sent __last,
 		 const _Tp& __value, _Proj __proj = {}) const
       {
-	auto __pred = [&] (auto&& __arg) {
+	auto __pred = [&] (auto&& __arg) -> bool {
 	  return std::forward<decltype(__arg)>(__arg) == __value;
 	};
 	return ranges::remove_if(__first, __last,
@@ -2537,11 +2537,11 @@ namespace ranges
 	else
 	  {
 	    if (__first == __last)
-	      return {std::move(__first), std::move(__first)};
+	      return {__first, __first};
 
 	    while (std::__invoke(__pred, std::__invoke(__proj, *__first)))
 	      if (++__first == __last)
-		return {std::move(__first), std::move(__first)};
+		return {__first, __first};
 
 	    auto __next = __first;
 	    while (++__next != __last)
@@ -3118,7 +3118,7 @@ namespace ranges
       operator()(const _Tp& __a, const _Tp& __b,
 		 _Comp __comp = {}, _Proj __proj = {}) const
       {
-	if (std::__invoke(std::move(__comp),
+	if (std::__invoke(__comp,
 			  std::__invoke(__proj, __b),
 			  std::__invoke(__proj, __a)))
 	  return __b;
@@ -3172,7 +3172,7 @@ namespace ranges
       operator()(const _Tp& __a, const _Tp& __b,
 		 _Comp __comp = {}, _Proj __proj = {}) const
       {
-	if (std::__invoke(std::move(__comp),
+	if (std::__invoke(__comp,
 			  std::__invoke(__proj, __a),
 			  std::__invoke(__proj, __b)))
 	  return __b;
@@ -3272,7 +3272,7 @@ namespace ranges
       operator()(const _Tp& __a, const _Tp& __b,
 		 _Comp __comp = {}, _Proj __proj = {}) const
       {
-	if (std::__invoke(std::move(__comp),
+	if (std::__invoke(__comp,
 			  std::__invoke(__proj, __b),
 			  std::__invoke(__proj, __a)))
 	  return {__b, __a};
-- 
2.31.1.362.g311531c9de