Introduction of read-only struct TargetFramework

It represents the and its domain concerns. Can be extended later.

src/Buildalyzer/TargetFramework.cs

@@ -0,0 +1,68 @@
+#nullable enable
+
+using System;
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Contracts;
+
+namespace Buildalyzer;
+
+/// <summary>Represents the target framework.</summary>
+public readonly struct TargetFramework : IEquatable<TargetFramework>
+{
+    /// <summary>No target framework.</summary>
+    public static TargetFramework None { get; }
+
+    private TargetFramework(string name) => _name = name;
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private readonly string? _name;
+
+    /// <summary>Indicates that the target framework is .NET (classic) framework version.</summary>
+    /// <remarks>
+    /// Because the .NET Core/.NET 5 TFMs are better defined, we just check if this is one of them and then negate.
+    /// </remarks>
+    public bool IsNetFramework
+        => _name is { Length: >= 2 }
+        && !IsNetCoreApp
+        && !IsNetStandard
+        && !IsNet;
+
+    public bool IsNetCoreApp
+        => _name is { Length: 14 }
+        && _name.StartsWith("netcoreapp");
+
+    public bool IsNetStandard
+        => _name is { Length: 14 }
+        && _name.StartsWith("netstandard");
+
+    public bool IsNet
+        => _name is { Length: 14 }
+        && _name.StartsWith("net")
+        && int.TryParse(_name[3..3], out int version)
+        && version >= 5;
+
+    /// <inheritdoc />
+    [Pure]
+    public override bool Equals([NotNullWhen(true)] object? obj)
+        => obj is TargetFramework other
+        && Equals(other);
+
+    /// <inheritdoc />
+    [Pure]
+    public bool Equals(TargetFramework other) => _name == other._name;
+
+    /// <inheritdoc />
+    [Pure]
+    public override int GetHashCode() => HashCode.Combine(_name);
+
+    /// <inheritdoc />
+    [Pure]
+    public override string ToString() => _name ?? string.Empty;
+
+    [Pure]
+    public static TargetFramework Parse(string? s)
+        => s is { Length: > 0 }
+        ? new TargetFramework(s.ToLowerInvariant())
+        : None;
+}

tests/Buildalyzer.Tests/TargetFrameworkFixture.cs

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+using NUnit.Framework;
+using Shouldly;
+
+namespace Buildalyzer.Tests;
+
+/// <remarks>
+/// From https://docs.microsoft.com/en-us/dotnet/standard/frameworks.
+/// </remarks>
+[TestFixture]
+public class TargetFrameworkFixture
+{
+    [TestCase("netstandard1.0")]
+    [TestCase("netstandard1.1")]
+    [TestCase("netstandard1.2")]
+    [TestCase("netstandard1.3")]
+    [TestCase("netstandard1.4")]
+    [TestCase("netstandard1.5")]
+    [TestCase("netstandard1.6")]
+    [TestCase("netstandard2.0")]
+    [TestCase("netstandard2.1")]
+    public void NetStandard(string s)
+    {
+        var tfm = TargetFramework.Parse(s);
+        tfm.IsNetFramework.ShouldBeFalse();
+        tfm.IsNetStandard.ShouldBeTrue();
+    }
+
+    [TestCase("netcoreapp1.0")]
+    [TestCase("netcoreapp1.1")]
+    [TestCase("netcoreapp2.0")]
+    [TestCase("netcoreapp2.1")]
+    [TestCase("netcoreapp2.2")]
+    [TestCase("netcoreapp3.0")]
+    [TestCase("netcoreapp3.1")]
+    public void NetCoreApp(string s)
+    {
+        var tfm = TargetFramework.Parse(s);
+        tfm.IsNetFramework.ShouldBeFalse();
+        tfm.IsNetCoreApp.ShouldBeTrue();
+    }
+
+    [TestCase("net5")] // This isn't an official TFM but we'll check it anyway
+    [TestCase("net5.0")]
+    [TestCase("net5.0-android")]
+    [TestCase("net5.0-ios")]
+    [TestCase("net5.0-macos")]
+    [TestCase("net5.0-tvos")]
+    [TestCase("net5.0-watchos")]
+    [TestCase("net5.0-windows")]
+    [TestCase("net6")] // This isn't an official TFM but we'll check it anyway
+    [TestCase("net6.0")]
+    [TestCase("net6.0-android")]
+    [TestCase("net6.0-ios")]
+    [TestCase("net6.0-macos")]
+    [TestCase("net6.0-tvos")]
+    [TestCase("net6.0-watchos")]
+    [TestCase("net6.0-windows")]
+    public void Net(string s)
+    {
+        var tfm = TargetFramework.Parse(s);
+        tfm.IsNetFramework.ShouldBeFalse();
+        tfm.IsNet.ShouldBeTrue();
+    }
+
+    [TestCase("net11")]
+    [TestCase("net20")]
+    [TestCase("net35")]
+    [TestCase("net40")]
+    [TestCase("net403")]
+    [TestCase("net45")]
+    [TestCase("net451")]
+    [TestCase("net452")]
+    [TestCase("net46")]
+    [TestCase("net461")]
+    [TestCase("net462")]
+    [TestCase("net47")]
+    [TestCase("net471")]
+    [TestCase("net472")]
+    [TestCase("net48")]
+    public void DotNetFramework(string s)
+    {
+        var tfm = TargetFramework.Parse(s);
+        tfm.IsNetFramework.ShouldBeTrue();
+    }
+
+    [TestCase("netcore")]
+    [TestCase("netcore45")]
+    [TestCase("netcore451")]
+    [TestCase("netmf")]
+    [TestCase("sl4")]
+    [TestCase("sl5")]
+    [TestCase("wp")]
+    [TestCase("wp7")]
+    [TestCase("wp75")]
+    [TestCase("wp8")]
+    [TestCase("wp81")]
+    [TestCase("wpa81")]
+    [TestCase("uap")]
+    [TestCase("uap10.0")]
+    public void Exotic(string s)
+    {
+        var tfm = TargetFramework.Parse(s);
+        tfm.IsNetFramework.ShouldBeTrue();
+    }
+}