Type.GetType: improve code analysis when throwOnError is provided

[weitzhandler]

Description

Please improve compiler the methods in System.Type where a throwOnError is applicable by specifying code-analysis.
We're not expecting null if throwOnError is true.

Proposal

namespace System

public abstract partial class Type : MemberInfo, IReflect
{
    [SupportedOSPlatform("windows")]
    public static Type? GetTypeFromCLSID(Guid clsid, bool throwOnError) =>
        GetTypeFromCLSID(clsid, null, throwOnError: throwOnError);

    [SupportedOSPlatform("windows")]
    public static Type? GetTypeFromCLSID(Guid clsid, string? server, bool throwOnError) => 
        Marshal.GetTypeFromCLSID(clsid, server, throwOnError);

    [SupportedOSPlatform("windows")]
    public static Type? GetTypeFromProgID(string progID, bool throwOnError) => 
        GetTypeFromProgID(progID, null, throwOnError: throwOnError);

    [SupportedOSPlatform("windows")]
    public static Type? GetTypeFromProgID(string progID, string? server, bool throwOnError) =>
        Marshal.GetTypeFromProgID(progID, server, throwOnError);
}

The above should be changed to:

public abstract partial class Type : MemberInfo, IReflect
{
    [SupportedOSPlatform("windows")]
    public static Type? GetTypeFromCLSID(Guid clsid, [NotNullWhen(true)] bool throwOnError) =>
        GetTypeFromCLSID(clsid, null, throwOnError: throwOnError);
    [SupportedOSPlatform("windows")]
    public static Type? GetTypeFromCLSID(Guid clsid, string? server, [NotNullWhen(true)] bool throwOnError) =>
        Marshal.GetTypeFromCLSID(clsid, server, throwOnError);

    [SupportedOSPlatform("windows")]
    public static Type? GetTypeFromProgID(string progID, [NotNullWhen(true)] bool throwOnError) =>
        GetTypeFromProgID(progID, null, throwOnError: throwOnError);
    [SupportedOSPlatform("windows")]
    public static Type? GetTypeFromProgID(string progID, string? server, [NotNullWhen(true)] bool throwOnError) =>
        Marshal.GetTypeFromProgID(progID, server, throwOnError);
}

Feel free to assign me if approved.

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[huoyaoyuan]

This is an API proposal, not performance topic.

[NotNullWhen(true)] on parameter means that the parameter is not null when return value is true. Currently there's no attribute to specify the desired behavior (return value is not null when parameter is true).

[weitzhandler]

@huoyaoyuan it was opened as a performance topic by accident. OTOH it's not exactly an API change but rather a small convenience improvement to existing implementation.

Anyway yes you're right [NotNullWhen] doesn't address this behavior.