Fix ranges::is_permutation's helper lambdas (microsoft#3113)

Co-authored-by: Casey Carter <cartec69@gmail.com>
CaseyCarter · Oct 6, 2022 · 787eb80 · 787eb80
1 parent d2c242d
commit 787eb80
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Showing 2 changed files with 13 additions and 2 deletions.
diff --git a/stl/inc/algorithm b/stl/inc/algorithm
@@ -957,7 +957,7 @@ namespace ranges {
                 // We've trimmed matching prefixes and matching suffixes.
                 // Now we need to compare each range's prefix to the other range's suffix.
 
-                const auto _ProjectedPred = [&]<class _Ty1, class _Ty2>(_Ty1&& _Left, _Ty2&& _Right) {
+                const auto _ProjectedPred = [&]<class _Ty1, class _Ty2>(_Ty1&& _Left, _Ty2&& _Right) -> bool {
                     return _STD invoke(_Pred, _STD invoke(_Proj1, _STD forward<_Ty1>(_Left)),
                         _STD invoke(_Proj2, _STD forward<_Ty2>(_Right)));
                 };
@@ -1046,7 +1046,7 @@ namespace ranges {
                 // We've trimmed matching prefixes and matching suffixes.
                 // Now we need to compare each range's prefix to the other range's suffix.
 
-                const auto _ProjectedPred = [&]<class _Ty1, class _Ty2>(_Ty1&& _Left, _Ty2&& _Right) {
+                const auto _ProjectedPred = [&]<class _Ty1, class _Ty2>(_Ty1&& _Left, _Ty2&& _Right) -> bool {
                     return _STD invoke(_Pred, _STD invoke(_Proj1, _STD forward<_Ty1>(_Left)),
                         _STD invoke(_Proj2, _STD forward<_Ty2>(_Right)));
                 };

diff --git a/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp b/tests/std/tests/P0896R4_ranges_alg_is_permutation/test.cpp
@@ -134,6 +134,17 @@ struct instantiator {
             assert(ranges::is_permutation(
                 r1, r2, {}, [](int n) { return n + 1; }, [](int n) { return n - 1; }));
         }
+        { // Test GH-2888: `<algorithm>`: `ranges::is_permutation`'s helper lambda does not specify return type
+            struct NonCopyableBool {
+                constexpr operator bool() {
+                    return true;
+                }
+
+                NonCopyableBool()                       = default;
+                NonCopyableBool(const NonCopyableBool&) = delete;
+            } b;
+            assert(ranges::is_permutation(range2, range2, [&](auto, auto) -> NonCopyableBool& { return b; }));
+        }
     }
 };