Merge branch 'master' into DRTVWR-530-maint

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diff --git a/indra/newview/tests/cppfeatures_test.cpp b/indra/newview/tests/cppfeatures_test.cpp
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+/**
+ * @file cppfeatures_test
+ * @author Vir
+ * @date 2021-03
+ * @brief cpp features
+ *
+ * $LicenseInfo:firstyear=2021&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2021, Linden Research, Inc.
+ * 
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ * 
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ * 
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ */
+
+// Tests related to newer C++ features, for verifying support across compilers and platforms
+
+#include "linden_common.h"
+#include "../test/lltut.h"
+
+namespace tut
+{
+
+struct cpp_features_test {};
+typedef test_group<cpp_features_test> cpp_features_test_t;
+typedef cpp_features_test_t::object cpp_features_test_object_t;
+tut::cpp_features_test_t tut_cpp_features_test("LLCPPFeatures");
+
+// bracket initializers
+// Can initialize containers or values using curly brackets
+template<> template<>
+void cpp_features_test_object_t::test<1>()
+{
+	S32 explicit_val{3};
+	ensure(explicit_val==3);
+
+	S32 default_val{};
+	ensure(default_val==0);
+	
+	std::vector<S32> fibs{1,1,2,3,5};
+	ensure(fibs[4]==5);
+}
+
+// auto
+//
+// https://en.cppreference.com/w/cpp/language/auto
+// 
+// Can use auto in place of a more complex type specification, if the compiler can infer the type
+template<> template<>
+void cpp_features_test_object_t::test<2>()
+{
+	std::vector<S32> numbers{3,6,9};
+
+	// auto element
+	auto& aval = numbers[1];
+	ensure("auto element", aval==6);
+
+	// auto iterator (non-const)
+	auto it = numbers.rbegin();
+	*it += 1;
+	S32 val = *it;
+	ensure("auto iterator", val==10);
+}
+
+// range for
+//
+// https://en.cppreference.com/w/cpp/language/range-for
+//
+// Can iterate over containers without explicit iterator
+template<> template<>
+void cpp_features_test_object_t::test<3>()
+{
+
+	// Traditional iterator for with container
+	//
+	// Problems:
+	// * Have to create a new variable for the iterator, which is unrelated to the problem you're trying to solve.
+	// * Redundant and somewhat fragile. Have to make sure begin() and end() are both from the right container.
+	std::vector<S32> numbers{3,6,9};
+	for (auto it = numbers.begin(); it != numbers.end(); ++it)
+	{
+		auto& n = *it;
+		n *= 2;
+	}
+	ensure("iterator for vector", numbers[2]==18);
+
+	// Range for with container
+	//
+	// Under the hood, this is doing the same thing as the traditional
+	// for loop above. Still uses begin() and end() but you don't have
+	// to access them directly.
+	std::vector<S32> numbersb{3,6,9};
+	for (auto& n: numbersb)
+	{
+		n *= 2;
+	}
+	ensure("range for vector", numbersb[2]==18);
+
+	// Range for over a C-style array.
+	//
+	// This is handy because the language determines the range automatically.
+	// Getting this right manually is a little trickier.
+	S32 pows[] = {1,2,4,8,16};
+	S32 sum{};
+	for (const auto& v: pows)
+	{
+		sum += v;
+	}
+	ensure("for C-array", sum==31);
+}
+
+// override specifier
+//
+// https://en.cppreference.com/w/cpp/language/override
+//
+// Specify that a particular class function is an override of a virtual function.
+// Benefits:
+// * Makes code somewhat easier to read by showing intent.
+// * Prevents mistakes where you think something is an override but it doesn't actually match the declaration in the parent class.
+// Drawbacks:
+// * Some compilers require that any class using override must use it consistently for all functions. 
+//   This makes switching a class to use override a lot more work. 
+
+class Foo
+{
+public:
+	virtual bool is_happy() const = 0;
+};
+
+class Bar: public Foo
+{
+public:
+	bool is_happy() const override { return true; } 
+	// Override would fail: non-const declaration doesn't match parent 
+	// bool is_happy() override { return true; } 
+	// Override would fail: wrong name
+	// bool is_happx() override { return true; } 
+};
+
+template<> template<>
+void cpp_features_test_object_t::test<4>()
+{
+	Bar b;
+	ensure("override", b.is_happy());
+}
+
+// final
+//
+// https://en.cppreference.com/w/cpp/language/final: "Specifies that a
+// virtual function cannot be overridden in a derived class or that a
+// class cannot be inherited from."
+
+class Vehicle
+{
+public:
+	virtual bool has_wheels() const = 0;
+};
+
+class WheeledVehicle: public Vehicle
+{
+public:
+	virtual bool has_wheels() const final override { return true; }
+};
+
+class Bicycle: public WheeledVehicle
+{
+public:
+	// Error: can't override final version in WheeledVehicle 
+	// virtual bool has_wheels() override const { return true; }
+};
+
+template<> template<>
+void cpp_features_test_object_t::test<5>()
+{
+	Bicycle bi;
+	ensure("final", bi.has_wheels());
+}
+
+// deleted function declaration
+//
+// https://en.cppreference.com/w/cpp/language/function#Deleted_functions
+//
+// Typical case: copy constructor doesn't make sense for a particular class, so you want to make
+// sure the no one tries to copy-construct an instance of the class, and that the
+// compiler won't generate a copy constructor for  you automatically.
+// Traditional fix is to declare a
+// copy constructor but never implement it, giving you a link-time error if anyone tries to use it.
+// Now you can explicitly declare a function to be deleted, which has at least two advantages over
+// the old way:
+// * Makes the intention clear
+// * Creates an error sooner, at compile time
+
+class DoNotCopy
+{
+public:
+	DoNotCopy() {}
+	DoNotCopy(const DoNotCopy& ref) = delete;
+};
+
+template<> template<>
+void cpp_features_test_object_t::test<6>()
+{
+	DoNotCopy nc; // OK, default constructor
+	//DoNotCopy nc2(nc); // No, can't copy
+	//DoNotCopy nc3 = nc; // No, this also calls copy constructor (even though it looks like an assignment)
+}
+
+// defaulted function declaration
+//
+// https://en.cppreference.com/w/cpp/language/function#Function_definition
+//
+// What about the complementary case to the deleted function declaration, where you want a copy constructor
+// and are happy with the default implementation the compiler will make (memberwise copy).
+// Now you can explicitly declare that too.
+// Usage: I guess it makes the intent clearer, but otherwise not obviously useful.
+class DefaultCopyOK
+{
+public:
+	DefaultCopyOK(): mVal(123) {}
+	DefaultCopyOK(const DefaultCopyOK&) = default;
+	S32 val() const { return mVal; }
+private:
+	S32 mVal;
+};
+
+template<> template<>
+void cpp_features_test_object_t::test<7>()
+{
+	DefaultCopyOK d; // OK
+	DefaultCopyOK d2(d); // OK
+	DefaultCopyOK d3 = d; // OK
+	ensure("default copy d", d.val()==123);
+	ensure("default copy d2", d.val()==d2.val());
+	ensure("default copy d3", d.val()==d3.val());
+}
+
+// initialize class members inline
+//
+// https://en.cppreference.com/w/cpp/language/data_members#Member_initialization
+//
+// Default class member values can be set where they are declared, using either brackets or =
+
+// It is preferred to skip creating a constructor if all the work can be done by inline initialization:
+// http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines.html#c45-dont-define-a-default-constructor-that-only-initializes-data-members-use-in-class-member-initializers-instead
+//
+class InitInline
+{
+public:
+	S32 mFoo{10};
+};
+
+class InitInlineWithConstructor
+{
+public:
+	// Here mFoo is not specified, so you will get the default value of 10.
+	// mBar is specified, so 25 will override the default value.
+	InitInlineWithConstructor():
+		mBar(25)
+	{}
+
+	// Default values set using two different styles, same effect.
+	S32 mFoo{10};
+	S32 mBar = 20;
+};
+
+template<> template<>
+void cpp_features_test_object_t::test<8>()
+{
+	InitInline ii;
+	ensure("init member inline 1", ii.mFoo==10);
+
+	InitInlineWithConstructor iici;
+	ensure("init member inline 2", iici.mFoo=10);
+	ensure("init member inline 3", iici.mBar==25);
+}
+
+// constexpr
+//
+// https://en.cppreference.com/w/cpp/language/constexpr
+//
+// Various things can be computed at compile time, and flagged as constexpr.
+constexpr S32 compute2() { return 2; }
+
+constexpr S32 ce_factorial(S32 n)
+{
+	if (n<=0)
+	{
+		return 1;
+	}
+	else
+	{
+		return n*ce_factorial(n-1);
+	}
+}
+
+template<> template<>
+void cpp_features_test_object_t::test<9>()
+{
+	S32 val = compute2();
+	ensure("constexpr 1", val==2);
+
+	// Compile-time factorial. You used to need complex templates to do something this useless.
+	S32 fac5 = ce_factorial(5);
+	ensure("constexpr 2", fac5==120);
+}
+
+// static assert
+//
+// https://en.cppreference.com/w/cpp/language/static_assert
+//
+// You can add asserts to be checked at compile time. The thing to be checked must be a constexpr.
+// There are two forms:
+// * static_assert(expr);
+// * static_assert(expr, message);
+//
+// Currently only the 2-parameter form works on windows. The 1-parameter form needs a flag we don't set.
+
+template<> template<>
+void cpp_features_test_object_t::test<10>()
+{
+	// static_assert(ce_factorial(6)==720); No, needs a flag we don't currently set.
+	static_assert(ce_factorial(6)==720, "bad factorial"); // OK
+}
+
+// type aliases
+//
+// https://en.cppreference.com/w/cpp/language/type_alias
+// 
+// You can use the "using" statement to create simpler templates that
+// are aliases for more complex ones. "Template typedef"
+
+// This makes stringmap<T> an alias for std::map<std::string, T>
+template<typename T>
+using stringmap = std::map<std::string, T>;
+
+template<> template<>
+void cpp_features_test_object_t::test<11>()
+{
+	stringmap<S32> name_counts{ {"alice", 3}, {"bob", 2} };
+	ensure("type alias", name_counts["bob"]==2);
+}
+
+// Other possibilities:
+
+// nullptr
+
+// class enums
+
+// std::unique_ptr and make_unique
+
+// std::shared_ptr and make_shared
+
+// lambdas
+
+// perfect forwarding
+
+// variadic templates
+
+// std::thread
+
+// std::mutex
+
+// thread_local
+
+// rvalue reference &&
+
+// move semantics
+
+// std::move
+
+// string_view
+
+} // namespace tut