[libc++][test] Fixes for hash<Emplaceable> and value discarding

[frederick-vs-ja]

Currently std::hash<Emplaceable>::operator() relies implicit conversion from int to size_t, which makes MSVC compelling. This PR switches to use static_cast.

In flat.map/flat.map.access/at_transparent.pass.cpp, there's one value-discarding use of at that wasn't marked TEST_IGNORE_NODISCARD. This PR adds the missing TEST_IGNORE_NODISCARD.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: A. Jiang (frederick-vs-ja)

Changes

Currently std::hash<Emplaceable>::operator() relies implicit conversion from int to size_t, which makes MSVC compelling. This PR switches to use static_cast.

In flat.map/flat.map.access/at_transparent.pass.cpp, there's one value-discarding use of at that wasn't marked TEST_IGNORE_NODISCARD. This PR adds the missing TEST_IGNORE_NODISCARD.

---

Full diff: https://github.com/llvm/llvm-project/pull/126566.diff

2 Files Affected:

• (modified) libcxx/test/std/containers/Emplaceable.h (+1-1)
• (modified) libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp (+1-1)

diff --git a/libcxx/test/std/containers/Emplaceable.h b/libcxx/test/std/containers/Emplaceable.h
index 1a4e14505fb21ed..001886eece7d75e 100644
--- a/libcxx/test/std/containers/Emplaceable.h
+++ b/libcxx/test/std/containers/Emplaceable.h
@@ -45,7 +45,7 @@ struct std::hash<Emplaceable> {
   typedef Emplaceable argument_type;
   typedef std::size_t result_type;
 
-  std::size_t operator()(const Emplaceable& x) const { return x.get(); }
+  std::size_t operator()(const Emplaceable& x) const { return static_cast<std::size_t>(x.get()); }
 };
 
 #endif // TEST_STD_VER >= 11
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
index 13edca915fd005c..456f12e0c0d29ff 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
@@ -103,7 +103,7 @@ int main(int, char**) {
     TransparentComparator c(transparent_used);
     std::flat_map<int, int, TransparentComparator> m(std::sorted_unique, {{1, 1}, {2, 2}, {3, 3}}, c);
     assert(!transparent_used);
-    m.at(Transparent<int>{3});
+    TEST_IGNORE_NODISCARD m.at(Transparent<int>{3});
     assert(transparent_used);
   }
 

[mordante]

Thanks, LGTM!