Start on API analyzers

Discord.Net.sln

@@ -1,6 +1,6 @@
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
-VisualStudioVersion = 15.0.26730.12
+VisualStudioVersion = 15.0.27130.0
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Discord.Net.Core", "src\Discord.Net.Core\Discord.Net.Core.csproj", "{91E9E7BD-75C9-4E98-84AA-2C271922E5C2}"
 EndProject
@@ -24,6 +24,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Discord.Net.Tests", "test\D
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Discord.Net.Webhook", "src\Discord.Net.Webhook\Discord.Net.Webhook.csproj", "{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Discord.Net.Analyzers", "src\Discord.Net.Analyzers\Discord.Net.Analyzers.csproj", "{BBA8E7FB-C834-40DC-822F-B112CB7F0140}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -130,6 +132,18 @@ Global
 		{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30}.Release|x64.Build.0 = Release|Any CPU
 		{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30}.Release|x86.ActiveCfg = Release|Any CPU
 		{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30}.Release|x86.Build.0 = Release|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Debug|x64.Build.0 = Debug|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Debug|x86.Build.0 = Debug|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Release|Any CPU.Build.0 = Release|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Release|x64.ActiveCfg = Release|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Release|x64.Build.0 = Release|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Release|x86.ActiveCfg = Release|Any CPU
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -141,6 +155,7 @@ Global
 		{688FD1D8-7F01-4539-B2E9-F473C5D699C7} = {288C363D-A636-4EAE-9AC1-4698B641B26E}
 		{6BDEEC08-417B-459F-9CA3-FF8BAB18CAC7} = {B0657AAE-DCC5-4FBF-8E5D-1FB578CF3012}
 		{9AFAB80E-D2D3-4EDB-B58C-BACA78D1EA30} = {CC3D4B1C-9DE0-448B-8AE7-F3F1F3EC5C3A}
+		{BBA8E7FB-C834-40DC-822F-B112CB7F0140} = {CC3D4B1C-9DE0-448B-8AE7-F3F1F3EC5C3A}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {D2404771-EEC8-45F2-9D71-F3373F6C1495}

src/Discord.Net.Analyzers/Discord.Net.Analyzers.csproj

@@ -0,0 +1,30 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <VersionPrefix>1.0.2</VersionPrefix>
+    <Authors>RogueException</Authors>
+    <PackageTags>discord;discordapp</PackageTags>
+    <PackageProjectUrl>https://github.com/RogueException/Discord.Net</PackageProjectUrl>
+    <PackageLicenseUrl>http://opensource.org/licenses/MIT</PackageLicenseUrl>
+    <RepositoryType>git</RepositoryType>
+    <RepositoryUrl>git://github.com/RogueException/Discord.Net</RepositoryUrl>
+    <AssemblyName>Discord.Net.Analyzers</AssemblyName>
+    <RootNamespace>Discord.Analyzers</RootNamespace>
+    <Description>A Discord.Net extension adding support for design-time analysis of the API usage.</Description>
+    <TargetFramework>netstandard1.3</TargetFramework>
+  </PropertyGroup>
+    <PropertyGroup Condition=" '$(TargetFramework)' == 'netstandard1.3' Or '$(TargetFramework)' == 'net45' ">
+      <DefineConstants>$(DefineConstants);FILESYSTEM;DEFAULTUDPCLIENT;DEFAULTWEBSOCKET</DefineConstants>
+    </PropertyGroup>
+    <PropertyGroup Condition=" '$(TargetFramework)' == 'netstandard1.3' ">
+      <DefineConstants>$(DefineConstants);FORMATSTR;UNIXTIME;MSTRYBUFFER;UDPDISPOSE</DefineConstants>
+    </PropertyGroup>
+    <PropertyGroup Condition=" '$(Configuration)' == 'Release' ">
+      <NoWarn>$(NoWarn);CS1573;CS1591</NoWarn>
+      <WarningsAsErrors>true</WarningsAsErrors>
+      <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis" Version="2.6.0" />
+    <PackageReference Include="Discord.Net.Commands" Version="1.0.2" />
+  </ItemGroup>
+</Project>

src/Discord.Net.Analyzers/GuildAccessAnalyzer.cs

@@ -0,0 +1,78 @@
+using System;
+using System.Collections.Immutable;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Discord.Commands;
+
+namespace Discord.Analyzers
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    public sealed class GuildAccessAnalyzer : DiagnosticAnalyzer
+    {
+        private const string DiagnosticId = "DNET0001";
+        private const string Title = "Limit command to Guild contexts.";
+        private const string MessageFormat = "Command method '{0}' is accessing 'Context.Guild' but is not restricted to Guild contexts.";
+        private const string Description = "Accessing 'Context.Guild' in a command without limiting the command to run only in guilds.";
+        private const string Category = "Design";
+
+        private static DiagnosticDescriptor Rule = new DiagnosticDescriptor(DiagnosticId, Title, MessageFormat, Category, DiagnosticSeverity.Warning, isEnabledByDefault: true, description: Description);
+
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Rule);
+
+        public override void Initialize(AnalysisContext context)
+        {
+            context.RegisterSyntaxNodeAction(AnalyzeMemberAccess, SyntaxKind.SimpleMemberAccessExpression);
+        }
+
+        private static void AnalyzeMemberAccess(SyntaxNodeAnalysisContext context)
+        {
+            // Bail out if the containing class doesn't derive from 'ModuleBase<T>'
+            var classNode = context.Node.FirstAncestorOrSelf<TypeDeclarationSyntax>();
+            var classSymbol = context.SemanticModel.GetSymbolInfo(classNode).Symbol as INamedTypeSymbol;
+            if (!DerivesFromModuleBase(classSymbol))
+                return;
+
+            // Bail out if the containing method isn't marked with '[Command]'
+            var methodNode = context.Node.FirstAncestorOrSelf<MethodDeclarationSyntax>();
+            var methodSymbol = context.SemanticModel.GetSymbolInfo(methodNode).Symbol;
+            var methodAttributes = methodSymbol.GetAttributes();
+            if (!methodAttributes.Any(a => a.AttributeClass.Name == nameof(CommandAttribute)))
+                return;
+
+            // Are you geting a property named 'Guild'?
+            var memberAccessSymbol = context.SemanticModel.GetSymbolInfo(context.Node).Symbol as IMethodSymbol;
+            if (memberAccessSymbol.AssociatedSymbol.Name == "Guild") //I guess?
+            {
+                // Is the '[RequireContext]' attribute not applied to either the method or the class, or doesn't contain 'ContextType.Guild'?
+                var ctxAttribute = methodAttributes.SingleOrDefault(_attributeDataPredicate)
+                    ?? classSymbol.GetAttributes().SingleOrDefault(_attributeDataPredicate);
+                if (ctxAttribute == null || ctxAttribute.ConstructorArguments.Any(arg => !arg.Value.Equals(ContextType.Guild)))
+                {
+                    // Report the diagnostic
+                    var diagnostic = Diagnostic.Create(Rule, context.Node.GetLocation(), methodSymbol.Name);
+                    context.ReportDiagnostic(diagnostic);
+                }
+            }
+        }
+
+        private static readonly Func<AttributeData, bool> _attributeDataPredicate = a => a.AttributeClass.Name == nameof(RequireContextAttribute);
+
+        private static readonly string _moduleBaseName = typeof(ModuleBase<>).Name;
+
+        private static bool DerivesFromModuleBase(INamedTypeSymbol symbol)
+        {
+            var bType = symbol.BaseType;
+            while (bType != null)
+            {
+                if (bType.MetadataName == _moduleBaseName)
+                    return true;
+
+                bType = bType.BaseType;
+            }
+            return false;
+        }
+    }
+}