[llvm] [ADT] Fix llvm::concat_iterator for `ValueT == common_base_class *` (PR #144744)

[Javier Lopez-Gomez via llvm-commits]

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@@ -532,6 +534,44 @@ TEST(STLExtrasTest, ConcatRangeADL) {
   EXPECT_THAT(concat<const int>(S0, S1), ElementsAre(1, 2, 3, 4));
 }
 
+TEST(STLExtrasTest, ConcatRangePtrToSameClass) {
+  some_namespace::some_struct S0{};
+  some_namespace::some_struct S1{};
+  SmallVector<some_namespace::some_struct *> V0{&S0};
+  SmallVector<some_namespace::some_struct *> V1{&S1, &S1};
+
+  // Dereferencing all iterators yields `some_namespace::some_struct *&`; no
+  // conversion takes place, `reference_type` is `some_namespace::some_struct
+  // *&`.
+  auto C = concat<some_namespace::some_struct *>(V0, V1);
+  static_assert(
+      std::is_same_v<decltype(*C.begin()), some_namespace::some_struct *&>);
+  EXPECT_THAT(C, ElementsAre(&S0, &S1, &S1));
+  // `reference_type` should still allow container modification.
+  llvm::for_each(C, [&S0](auto &i) {
+    if (i == &S0)
+      i = nullptr;
+  });
+  EXPECT_THAT(C, ElementsAre(nullptr, &S1, &S1));
+}
+
+TEST(STLExtrasTest, ConcatRangePtrToDerivedClass) {
+  some_namespace::some_struct S0{};
+  some_namespace::derives_from_some_struct S1{};
+  SmallVector<some_namespace::some_struct *> V0{&S0};
+  SmallVector<some_namespace::derives_from_some_struct *> V1{&S1, &S1};
+
+  // Dereferencing all iterators yields different (but convertible types);
+  // conversion takes place, `reference_type` is `some_namespace::some_struct
+  // *`.
----------------
jalopezg-git wrote:

`clang-format`'s decision :sweat_smile: -- fixed.

https://github.com/llvm/llvm-project/pull/144744