Analyzer

Diagnostic ID:
CA1831: Use AsSpan instead of Range-based indexers for string when appropriate
CA1846: Prefer AsSpan over Substring

Analyzer source

SDK: Built-in CA analyzers in .NET 5 SDK or later

Version: SDK 8.0.100-preview.7.23376.3

Describe the bug

The following code generates CA1831: Use AsSpan instead of Range-based indexers for string when appropriate:

void Foo(string str, int position)
{
    var foo = string.Concat(str[0..position], str.AsSpan(position + 1));
}

And the following code generates CA1846: Prefer AsSpan over Substring:

void Foo(string str, int position)
{
    var foo = string.Concat(str.Substring(0, position), str.Substring(position + 1));
}

All is good. In both cases, an analyzer warning is issued suggesting more efficient code. However, if I combine these two - use the range syntax in one argument and Substring in the other, like this:

void Foo(string str, int position)
{
    var foo = string.Concat(str[0..position], str.Substring(position + 1));
}

Suddenly, no diagnostic is issued. Both analyzers are silent. I think this code should produce a warning as well, be it either CA1831 or CA1846, or both.