this check feels real bit strange to me. so null or "+" is okay but "" not okay?

ping @jcouv

I would check for string.IsNullOrWhitespace(...) ? null : xxx

It feels like such a helper method is likely to already exist. Can you double-check?

fwiw @jcouv . i do find it odd that there is this restriction in the core API. i.e. you allow null. you allow whitespace. you allow normal text. but you basically don't allow the empty string. seems... string to me. But if you really want that, then this change seems ok :)

@chborl small nit. could you just make this:

else if (expr is IdentifierName name) { ...

Then you don't need the multiple casts.

@chborl since 'null' is allowed, this check should be:

elementNamesBuilder.Add(name.Identifier.ValueText == "" ? null : name.Identifier.ValueText)

@CyrusNajmabadi I agree the restriction is a bit strange, but arguably this PR demonstrates why it is useful: it helps guide users to pass null rather than empty, when they want to represent missing names ;-)

@jcouv so whitespace is also okay? just not empty string? is empty string used as some kind of special state marker? is that why empty string is explicitly blocked?

@jcouv asking since I saw Chery changed back from IsNullOrWhitespace to checking explicitly just "" string.

will null or whitespaces input will change any outcome of the API?

Correct, you can create a tuple symbol with illegal names, but we block empty strings.

This check was added in PR #14958
The most relevant comment I could find is that "fields can't have blank names".

This was tested explicitly:

        [Fact]
        public void CreateTupleTypeSymbol2_BadNames()
        {
            var comp = CSharpCompilation.Create("test", references: new[] { MscorlibRef });

            ITypeSymbol intType = comp.GetSpecialType(SpecialType.System_Int32);

            // illegal C# identifiers and blank
            var tuple2 = comp.CreateTupleTypeSymbol(ImmutableArray.Create(intType, intType), ImmutableArray.Create("123", " "));
            Assert.Equal(new[] { "123", " " }, GetTupleElementNames(tuple2));

            // reserved identifiers
            var tuple3 = comp.CreateTupleTypeSymbol(ImmutableArray.Create(intType, intType), ImmutableArray.Create("return", "class"));
            Assert.Equal(new[] { "return", "class" }, GetTupleElementNames(tuple3));
        }