Math: propagate Debug flags in Vector debug printer.

Such as being able to print the contents as hexadecimal. Doing this just
for Vector and not any other math types, as those are all floating point
where it doesn't make sense. And for Nanoseconds, which are integers,
hexadecimal printing makes no sense either.

src/Magnum/Math/Test/VectorTest.cpp

@@ -119,6 +119,7 @@ struct VectorTest: TestSuite::Tester {
 
     void debug();
     void debugPacked();
+    void debugPropagateFlags();
 };
 
 /* What's a typedef and not a using differs from the typedefs in root Magnum
@@ -197,7 +198,8 @@ VectorTest::VectorTest() {
               &VectorTest::strictWeakOrdering,
 
               &VectorTest::debug,
-              &VectorTest::debugPacked});
+              &VectorTest::debugPacked,
+              &VectorTest::debugPropagateFlags});
 }
 
 void VectorTest::construct() {
@@ -1332,6 +1334,14 @@ void VectorTest::debugPacked() {
     CORRADE_COMPARE(out.str(), "{0.5, 15, 1, 1} Vector(0, 0, 0, 0)\n");
 }
 
+void VectorTest::debugPropagateFlags() {
+    std::ostringstream out;
+    /* The modifier shouldn't become persistent for values after. The nospace
+       modifier shouldn't get propagated. */
+    Debug{&out} << ">" << Debug::nospace  << Debug::hex << Vector2i(0xab, 0xcd) << Vector2i(12, 13);
+    CORRADE_COMPARE(out.str(), ">Vector(0xab, 0xcd) Vector(12, 13)\n");
+}
+
 }}}}
 
 CORRADE_TEST_MAIN(Magnum::Math::Test::VectorTest)

src/Magnum/Math/Vector.h

@@ -1316,15 +1316,24 @@ template<std::size_t size, class T> inline BitVector<size> notEqual(const Vector
 #ifndef CORRADE_SINGLES_NO_DEBUG
 /** @debugoperator{Vector} */
 template<std::size_t size, class T> Debug& operator<<(Debug& debug, const Vector<size, T>& value) {
-    /** @todo might make sense to propagate the flags also, for hex value
-        printing etc */
+    /* Nested values should get printed with the same flags, so make all
+       immediate flags temporarily global -- except NoSpace, unless it's also
+       set globally */
+    const Utility::Debug::Flags prevFlags = debug.flags();
+    debug.setFlags(prevFlags | (debug.immediateFlags() & ~Utility::Debug::Flag::NoSpace));
+
     const bool packed = debug.immediateFlags() >= Debug::Flag::Packed;
     debug << (packed ? "{" : "Vector(") << Debug::nospace;
     for(std::size_t i = 0; i != size; ++i) {
         if(i != 0) debug << Debug::nospace << ",";
         debug << value[i];
     }
-    return debug << Debug::nospace << (packed ? "}" : ")");
+    debug << Debug::nospace << (packed ? "}" : ")");
+
+    /* Reset the original flags back */
+    debug.setFlags(prevFlags);
+
+    return debug;
 }
 
 /* Explicit instantiation for commonly used types */