[clang] [clang] __is_trivially_equality_comparable for types containing lambdas (PR #68506)

[Amirreza Ashouri via cfe-commits]

https://github.com/AMP999 created https://github.com/llvm/llvm-project/pull/68506

Lambdas (closure types) are trivially equality-comparable iff they are
non-capturing, because non-capturing lambdas are convertible to function
pointers: if (lam1 == lam2) compiles, then lam1 and lam2 must have
the same type, and be always-equal, and be empty.

>From ae2cd56b1c68353aae6c74524e71973ce6ca6904 Mon Sep 17 00:00:00 2001
From: Amirreza Ashouri <ar.ashouri999 at gmail.com>
Date: Sat, 7 Oct 2023 19:02:34 +0330
Subject: [PATCH 1/2] [clang] Rename some misleading names (Non-functional)
 These names could be misleading; should we change them to
 `NonTriviallyComparable` instead?

---
 clang/test/SemaCXX/type-traits.cpp | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/clang/test/SemaCXX/type-traits.cpp b/clang/test/SemaCXX/type-traits.cpp
index a35689d52978fcc..a1315f1966a6dd4 100644
--- a/clang/test/SemaCXX/type-traits.cpp
+++ b/clang/test/SemaCXX/type-traits.cpp
@@ -3160,11 +3160,18 @@ static_assert(!__is_trivially_equality_comparable(float), "");
 static_assert(!__is_trivially_equality_comparable(double), "");
 static_assert(!__is_trivially_equality_comparable(long double), "");
 
-struct TriviallyEqualityComparableNoDefaultedComparator {
+struct NonTriviallyEqualityComparableNoComparator {
   int i;
   int j;
 };
-static_assert(!__is_trivially_equality_comparable(TriviallyEqualityComparableNoDefaultedComparator), "");
+static_assert(!__is_trivially_equality_comparable(NonTriviallyEqualityComparableNoComparator), "");
+
+struct NonTriviallyEqualityComparableNonDefaultedComparator {
+  int i;
+  int j;
+  bool operator==(const NonTriviallyEqualityComparableNonDefaultedComparator&);
+};
+static_assert(!__is_trivially_equality_comparable(NonTriviallyEqualityComparableNonDefaultedComparator), "");
 
 #if __cplusplus >= 202002L
 
@@ -3177,7 +3184,7 @@ struct TriviallyEqualityComparable {
 
   bool operator==(const TriviallyEqualityComparable&) const = default;
 };
-static_assert(__is_trivially_equality_comparable(TriviallyEqualityComparable), "");
+static_assert(__is_trivially_equality_comparable(TriviallyEqualityComparable));
 
 struct TriviallyEqualityComparableContainsArray {
   int a[4];

>From ef0ad97b1dee9f4d7547f551b4b8b96a51221c51 Mon Sep 17 00:00:00 2001
From: Amirreza Ashouri <ar.ashouri999 at gmail.com>
Date: Sat, 7 Oct 2023 19:07:32 +0330
Subject: [PATCH 2/2] [clang] __is_trivially_equality_comparable for types
 containing lambdas

Lambdas (closure types) are trivially equality-comparable iff they are
non-capturing, because non-capturing lambdas are convertible to function
pointers: if (lam1 == lam2) compiles, then lam1 and lam2 must have
the same type, and be always-equal, and be empty.
---
 clang/lib/AST/Type.cpp             |  2 ++
 clang/test/SemaCXX/type-traits.cpp | 11 +++++++++++
 2 files changed, 13 insertions(+)

diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
index 4c433f7fe9daca0..f0e419de3b1ee84 100644
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -2663,6 +2663,8 @@ static bool
 HasNonDeletedDefaultedEqualityComparison(const CXXRecordDecl *Decl) {
   if (Decl->isUnion())
     return false;
+  if (Decl->isLambda())
+    return Decl->captures().empty() && (Decl->getLambdaCaptureDefault() == LCD_None);
 
   auto IsDefaultedOperatorEqualEqual = [&](const FunctionDecl *Function) {
     return Function->getOverloadedOperator() ==
diff --git a/clang/test/SemaCXX/type-traits.cpp b/clang/test/SemaCXX/type-traits.cpp
index a1315f1966a6dd4..275ddcbae73930d 100644
--- a/clang/test/SemaCXX/type-traits.cpp
+++ b/clang/test/SemaCXX/type-traits.cpp
@@ -3200,6 +3200,17 @@ struct TriviallyEqualityComparableContainsMultiDimensionArray {
 };
 static_assert(__is_trivially_equality_comparable(TriviallyEqualityComparableContainsMultiDimensionArray));
 
+auto GetNonCapturingLambda() { return [](){ return 42; }; }
+
+struct TriviallyEqualityComparableContainsLambda {
+  [[no_unique_address]] decltype(GetNonCapturingLambda()) l;
+  int i;
+
+  bool operator==(const TriviallyEqualityComparableContainsLambda&) const = default;
+};
+static_assert(!__is_trivially_equality_comparable(decltype(GetNonCapturingLambda()))); // padding
+static_assert(__is_trivially_equality_comparable(TriviallyEqualityComparableContainsLambda));
+
 struct TriviallyEqualityComparableNonTriviallyCopyable {
   TriviallyEqualityComparableNonTriviallyCopyable(const TriviallyEqualityComparableNonTriviallyCopyable&);
   ~TriviallyEqualityComparableNonTriviallyCopyable();