<inheritdoc cref> has bad default for path attribute, leading to senseless inherited doc

[AArnott]

Version Used: 16.8 (30313.166.master)

Steps to Reproduce:

public class C
{
    /// <param name="a"><inheritdoc cref="M(int,int)" path="/param[@name='a']"/></param>
    public void M(int a)
    {
        if (a > 0)
        {
        }
    }

    /// <summary>summary</summary>
    /// <param name="a">A description</param>
    /// <param name="b">B description</param>
    public void M(int a, int b)
    {
        if (a > 0 || b > 0)
        {
        }
    }
}

Expected Behavior:

I expect the default path to provide the same meaning as the explicitly specified path, as shown here:

Actual Behavior:

Instead, I see a concatenation of all param docs together, with not so much as a delimiter:

[sharwell]

Currently, for the example scenario the path attribute is defaulting to /param/node()[not(self::overloads)]. The implementation for the default path attribute value is:

roslyn/src/Workspaces/Core/Portable/Shared/Extensions/ISymbolExtensions.cs

Lines 528 to 550 in 73864c7

	static string BuildXPathForElement(XElement element)
	{
	if (ElementNameIs(element, "member") || ElementNameIs(element, "doc"))
	{
	// Avoid string concatenation allocations for inheritdoc as a top-level element
	return "/*/node()[not(self::overloads)]";
	}
	var path = "/node()[not(self::overloads)]";
	for (var current = element; current != null; current = current.Parent)
	{
	var currentName = current.Name.ToString();
	if (ElementNameIs(current, "member") || ElementNameIs(current, "doc"))
	{
	// Allow <member> and <doc> to be used interchangeably
	currentName = "*";
	}
	path = "/" + currentName + path;
	}
	return path;
	}

The code needs to be updated to recognize that the containing param element has a name attribute, and add a predicate:

-/param/node()[not(self::overloads)]
+/param[@name="a"]/node()[not(self::overloads)]

[sharwell]

💡 The tests for inheritdoc behavior are mostly in: https://github.com/dotnet/roslyn/blob/master/src/EditorFeatures/Test2/IntelliSense/IntellisenseQuickInfoBuilderTests_Inheritdoc.vb