Allow std::initializer_list constructors in constexpr expressions
diff --git a/test/constexpr.cpp b/test/constexpr.cpp
new file mode 100644
index 0000000..a327c14
--- /dev/null
+++ b/test/constexpr.cpp
@@ -0,0 +1,52 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2022 Alex Richardson <alexrichardson@google.com>
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include "main.h"
+
+EIGEN_DECLARE_TEST(constexpr) {
+ // Clang accepts (some of) this code when using C++14/C++17, but GCC does not like
+ // the fact that `T array[Size]` inside Eigen::internal::plain_array is not initialized
+ // until after the constructor returns:
+ // error: member ‘Eigen::internal::plain_array<int, 9, 0, 0>::array’ must be initialized by mem-initializer in
+ // ‘constexpr’ constructor
+#if EIGEN_COMP_CXXVER >= 20 || defined(__clang__)
+ constexpr Matrix3i mat({{1, 2, 3}, {4, 5, 6}, {7, 8, 9}});
+ VERIFY_IS_EQUAL(mat.size(), 9);
+ VERIFY_IS_EQUAL(mat(0, 0), 1);
+ static_assert(mat.coeff(0,1) == 2);
+ constexpr Array33i arr({{1, 2, 3}, {4, 5, 6}, {7, 8, 9}});
+ VERIFY_IS_EQUAL(arr(0, 0), 1);
+ VERIFY_IS_EQUAL(arr.size(), 9);
+ static_assert(arr.coeff(0,1) == 2);
+ // Also check dynamic size arrays/matrices with fixed-size storage (currently
+ // only works if all elements are initialized, since otherwise the compiler
+ // complains about uninitialized trailing elements.
+ constexpr Matrix<int, Eigen::Dynamic, Eigen::Dynamic, 0, 3, 3> dyn_mat({{1, 2, 3}, {4, 5, 6}, {7, 8, 9}});
+ VERIFY_IS_EQUAL(dyn_mat.size(), 9);
+ VERIFY_IS_EQUAL(dyn_mat(0, 0), 1);
+ static_assert(dyn_mat.coeff(0,1) == 2);
+ constexpr Array<int, Eigen::Dynamic, Eigen::Dynamic, 0, 3, 3> dyn_arr({{1, 2, 3}, {4, 5, 6}, {7, 8, 9}});
+ VERIFY_IS_EQUAL(dyn_arr(0, 0), 1);
+ VERIFY_IS_EQUAL(dyn_arr.size(), 9);
+ static_assert(dyn_arr.coeff(0,1) == 2);
+#endif // EIGEN_COMP_CXXVER >= 20 || defined(__clang__)
+}
+
+// Check that we can use the std::initializer_list constructor for constexpr variables.
+#if EIGEN_COMP_CXXVER >= 20
+// EIGEN_MAKE_UNALIGNED_ARRAY_ASSERT() will fail constexpr evaluation unless
+// we have std::is_constant_evaluated().
+constexpr Matrix<int, 2, 2> global_mat({{1, 2}, {3, 4}});
+
+EIGEN_DECLARE_TEST(constexpr_global) {
+ VERIFY_IS_EQUAL(global_mat.size(), 4);
+ VERIFY_IS_EQUAL(global_mat(0, 0), 1);
+ static_assert(global_mat.coeff(0,0) == 1);
+}
+#endif // EIGEN_COMP_CXXVER >= 20