Issue 6378 - [emscripten] Make DependentString constexpr

test/compiled/String.cpp

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 #include <string>
 #include <gtest/gtest.h>
 #include "compiled/String.h"
 
 ABP_NS_USING
 
+void checkConstexprTemplateCtor()
+{
+  static constexpr DependentString s(u"Test string");
+}
+
+void checkConstexprInvalidCtor()
+{
+  static constexpr DependentString s;

[sergei, 2018/03/16 13:43:27]

What is the reason to have `static` variables?

[René Jeschke, 2018/03/16 17:00:47]

It's an old habit. As I am using 'const' a lot, I want to make a difference
between 'is-not-gonna-change' and 'does-never-ever-change'. E.g. 'const len =
strlen(chars);' and 'static const len = 10;'.

I can remove the static modifier it it bothers someone.

[hub, 2018/03/16 17:11:32]

Yes, please.

+  static_assert(s.is_invalid(), "String should be invalid");
+}
+
+void checkConstexprCtor()
+{
+  static const String::value_type chars[] = u"Test string";
+  static const String::size_type length = sizeof(chars) / sizeof(chars[0]) - 1;
+  static constexpr DependentString s(chars, length);
+}
+
+void checkConstexprFuncsAndOps()
+{
+  static constexpr DependentString s = u"Test string"_str;
+  static constexpr DependentString s2 = u"Test string"_str;
+
+  static_assert(s.length() == s2.length(), "Length should be equal");
+  static_assert(s.equals(s2), "Strings should be equal");
+  static_assert(s == s2, "Strings should be equal");
+
+  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] == 'T', "First character should be 'T'");
+  static_assert(s[1] == 'e', "Second character should be 'e'");
+}
+
 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>(ABP_TEXT("some-string"_str)));
   EXPECT_FALSE(lexical_cast<bool>(ABP_TEXT(""_str)));
   EXPECT_FALSE(lexical_cast<bool>(DependentString()));
 }
 
 TEST(TestStringLexicalCast, toOwnedString)
 {
   EXPECT_EQ(ABP_TEXT("some-string"_str), lexical_cast<OwnedString>(ABP_TEXT("some-string"_str)));
   EXPECT_EQ(ABP_TEXT(""_str), lexical_cast<OwnedString>(ABP_TEXT(""_str)));
 }