Document warning waves.

.openpublishing.redirection.csharp.json

@@ -151,6 +151,10 @@
             "source_path_from_root": "/docs/csharp/lambda-expressions.md",
             "redirect_url": "/dotnet/csharp/language-reference/operators/lambda-expressions"
         },
+        {
+            "source_path_from_root": "/docs/csharp/language-reference/compiler-messages/cs8892.md",
+            "redirect_url": "/dotnet/csharp/language-reference/compiler-messages/warning-waves#cs8892"
+        },
         {
             "source_path_from_root": "/docs/csharp/language-reference/compiler-options/addmodule-compiler-option.md",
             "redirect_url": "/dotnet/csharp/language-reference/compiler-options/inputs"

docs/csharp/language-reference/compiler-messages/snippets/ImportedTypes/ImportedTypes.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

docs/csharp/language-reference/compiler-messages/snippets/ImportedTypes/Types.cs

@@ -0,0 +1,9 @@
+namespace ImportedTypes;
+
+// <DeclareImportedType>
+public struct Struct
+{
+    private string data = String.Empty;
+    public Struct() { }
+}
+// </DeclareImportedType>

docs/csharp/language-reference/compiler-messages/snippets/WarningWaves/Program.cs

@@ -0,0 +1,31 @@
+// See https://aka.ms/new-console-template for more information
+
+namespace WarningWaves;
+
+public static class Program
+{
+    // <MultipleEntryPoints>
+    public static void Main()
+    {
+        RunProgram();
+    }
+
+    // CS8892
+    public static async Task Main(string[] args)
+    {
+        await RunProgramAsync();
+    }
+    // </MultipleEntryPoints>
+
+    private static void RunProgram()
+    {
+        WaveFive.Examples();
+    }
+
+    private static async Task RunProgramAsync()
+    {
+        RunProgram();
+        await Task.Yield();
+    }
+}
+

docs/csharp/language-reference/compiler-messages/snippets/WarningWaves/WarningWaves.csproj

@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <WarningLevel>7</WarningLevel>
+    <AnalysisLevel>preview</AnalysisLevel>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\ImportedTypes\ImportedTypes.csproj" />
+  </ItemGroup>
+
+</Project>

docs/csharp/language-reference/compiler-messages/snippets/WarningWaves/WaveFive.cs

@@ -0,0 +1,200 @@
+using System;
+using ImportedTypes;
+
+namespace WarningWaves;
+
+public class WaveFive
+{
+    public class Src
+    {
+        public bool Select<T>(Func<int, T> selector) => true;
+    }
+
+    public class Src2
+    {
+        public int Select<T>(Func<int, T> selector) => 0;
+    }
+
+    public static void Examples()
+    {
+        var w = new WaveFive();
+
+        w.M(w);
+
+        QueryExpression();
+        QueryExpressionNoWarn();
+
+    }
+
+    private static void QueryExpression()
+    {
+        //<QueryPrecedence>
+        bool b = true;
+        var source = new Src();
+        b = true;
+        source = new Src();
+        var a = b && from c in source select c;
+        Console.WriteLine(a);
+
+        var indexes = new Src2();
+        int[] array = { 1, 2, 3, 4, 5, 6, 7 };
+        var range = array[0..from c in indexes select c];
+        //</QueryPrecedence>
+    }
+
+    private static void QueryExpressionNoWarn()
+    {
+        //<QueryPrecedenceNoWarn>
+        bool b = true;
+        var source = new Src();
+        b = true;
+        source = new Src();
+        var a = b && (from c in source select c);
+        Console.WriteLine(a);
+
+        var indexes = new Src2();
+        int[] array = { 1, 2, 3, 4, 5, 6, 7 };
+        var range = array[0..(from c in indexes select c)];
+        //</QueryPrecedenceNoWarn>
+    }
+    // <StaticTypeAsIs>
+    static class StaticClass
+    {
+        public static void Thing() { }
+    }
+
+    void M(object o)
+    {
+        // warning: cannot use a static type in 'is' or 'as'
+        if (o is StaticClass)
+        {
+            Console.WriteLine("Can't happen");
+        }
+        else
+        {
+            Console.WriteLine("o is not an instance of a static class");
+        }
+    }
+    // </StaticTypeAsIs>
+
+    // <StructsArentNull>
+    class Program
+    {
+        public static void M(S s)
+        {
+            if (s == null) { } // CS8073: The result of the expression is always 'false'
+            if (s != null) { } // CS8073: The result of the expression is always 'true'
+        }
+    }
+
+    struct S
+    {
+        public static bool operator ==(S s1, S s2) => s1.Equals(s2);
+        public static bool operator !=(S s1, S s2) => !s1.Equals(s2);
+        public override bool Equals(object? other)
+        {
+            // Implementation elided
+            return false;
+        }
+        public override int GetHashCode() => 0;
+
+        // Other details elided...
+    }
+    // </StructsArentNull>
+
+    // <StaticTypeInInterface>
+    public static class Utilities
+    {
+        // elided
+    }
+
+    public interface IUtility
+    {
+        // CS8897
+        public void SetUtility(Utilities u);
+
+        // CS8898
+        public Utilities GetUtility();
+    }
+    // </StaticTypeInInterface>
+
+
+    // <DefiniteAssignmentWarnings>
+    public struct DefiniteAssignmentWarnings
+    {
+        // CS8880
+        public Struct Property { get; }
+        // CS8881
+        private Struct field;
+
+        // CS8882
+        public void Method(out Struct s)
+        {
+
+        }
+
+        public DefiniteAssignmentWarnings(int dummy)
+        {
+            // CS8883
+            Struct v2 = Property;
+            // CS8884
+            Struct v3 = field;
+            // CS8885:
+            DefiniteAssignmentWarnings p2 = this;
+        }
+
+        public static void Method2(out Struct s1)
+        {
+            // CS8886
+            var s2 = s1;
+            s1 = default;
+        }
+
+        public static void UseLocalStruct()
+        {
+            Struct r1;
+            var r2 = r1;
+        }
+    }
+    // </DefiniteAssignmentWarnings>
+
+
+    // <DefiniteAssignment>
+    public struct DefiniteAssignmentNoWarnings
+    {
+        // CS8880
+        public Struct Property { get; } = default;
+        // CS8881
+        private Struct field = default;
+
+        // CS8882
+        public void Method(out Struct s)
+        {
+            s = default;
+        }
+
+        public DefiniteAssignmentNoWarnings(int dummy)
+        {
+            // CS8883
+            Struct v2 = Property;
+            // CS8884
+            Struct v3 = field;
+            // CS8885:
+            DefiniteAssignmentNoWarnings p2 = this;
+        }
+
+        public static void Method2(out Struct s1)
+        {
+            // CS8886
+            s1 = default;
+            var s2 = s1;
+        }
+
+        public static void UseLocalStruct()
+        {
+            Struct r1 = default;
+            var r2 = r1;
+        }
+    }
+    // </DefiniteAssignment>
+}

docs/csharp/language-reference/compiler-messages/snippets/WarningWaves/WaveSeven.cs

@@ -0,0 +1,7 @@
+namespace WarningWaves;
+
+// <NoLowercaseTypes>
+public class lowercasename
+{
+}
+// </NoLowercaseTypes>