Issue 6378 - [emscripten] Make DependentString constexpr

test/compiled/String.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
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  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include <string>
 #include <gtest/gtest.h>
 #include "compiled/String.h"
 
 ABP_NS_USING
 
+TEST(TestString, checkConstexprCorrectness)
+{
+  static constexpr DependentString s(u"Hello world!");
+  static constexpr DependentString s2;
+
+  static_assert(s.length() == 12, "Length should be 12");
+
+  static_assert(!s.empty(), "String should not be empty");
+  static_assert(!s.is_writable(), "String should not be writable");
+  static_assert(!s.is_deleted(), "String should not be deleted");
+
+  static_assert(s.data()[0] == 'H', "First character should be 'H'");
+  static_assert(s[1] == 'e', "Second character should be 'e'");
+
+  static_assert(s2.is_invalid(), "String should be invalid");
+}
+
 TEST(TestString, constructInvalidDependentString)
 {
   DependentString s;
   EXPECT_TRUE(s.is_invalid());
 
   DependentString s2(s);
   EXPECT_TRUE(s2.is_invalid());
 }
 
 TEST(TestString, constructInvalidOwnedString)
@@ skipping 134 matching lines @@
   EXPECT_FALSE(lexical_cast<bool>(u"some-string"_str));
   EXPECT_FALSE(lexical_cast<bool>(u""_str));
   EXPECT_FALSE(lexical_cast<bool>(DependentString()));
 }
 
 TEST(TestStringLexicalCast, toOwnedString)
 {
   EXPECT_EQ(u"some-string"_str, lexical_cast<OwnedString>(u"some-string"_str));
   EXPECT_EQ(u""_str, lexical_cast<OwnedString>(u""_str));
 }