Print helpful errors/warnings on generation failures

src/Microsoft.Windows.CsWin32/AnalyzerReleases.Unshipped.md

@@ -4,7 +4,9 @@
 ### New Rules
 Rule ID | Category | Severity | Notes
 --------|----------|----------|-------
+PInvoke000 | Functionality | Error | SourceGenerator
 PInvoke001 | Functionality | Warning | SourceGenerator
 PInvoke002 | Functionality | Warning | SourceGenerator
 PInvoke003 | Functionality | Warning | SourceGenerator
-PInvoke004 | Functionality | Warning | SourceGenerator
+PInvoke004 | Functionality | Warning | SourceGenerator
+PInvoke005 | Functionality | Warning | SourceGenerator

src/Microsoft.Windows.CsWin32/Generator.cs

@@ -1118,6 +1118,21 @@ internal static bool TryStripCommonNamespace(string fullNamespace, [NotNullWhen(
             return false;
         }
 
+        /// <summary>
+        /// Checks whether an exception was originally thrown because of a target platform incompatibility.
+        /// </summary>
+        /// <param name="ex">An exception that may be or contain a <see cref="PlatformIncompatibleException"/>.</param>
+        /// <returns><see langword="true"/> if <paramref name="ex"/> or an inner exception is a <see cref="PlatformIncompatibleException"/>; otherwise <see langword="false" />.</returns>
+        internal static bool IsPlatformCompatibleException(Exception? ex)
+        {
+            if (ex is null)
+            {
+                return false;
+            }
+
+            return ex is PlatformIncompatibleException || IsPlatformCompatibleException(ex?.InnerException);
+        }
+
         internal bool IsAttribute(CustomAttribute attribute, string ns, string name) => IsAttribute(this.mr, attribute, ns, name);
 
         internal bool TryGetHandleReleaseMethod(EntityHandle handleStructDefHandle, [NotNullWhen(true)] out string? releaseMethod)
@@ -1779,19 +1794,6 @@ protected virtual void Dispose(bool disposing)
             }
         }
 
-        /// <summary>
-        /// Checks whether an exception was originally thrown because of a target platform incompatibility.
-        /// </summary>
-        private static bool IsPlatformCompatibleException(Exception? ex)
-        {
-            if (ex is null)
-            {
-                return false;
-            }
-
-            return ex is PlatformIncompatibleException || IsPlatformCompatibleException(ex?.InnerException);
-        }
-
         private static T AddApiDocumentation<T>(string api, T memberDeclaration)
             where T : MemberDeclarationSyntax
         {

src/Microsoft.Windows.CsWin32/SourceGenerator.cs

@@ -23,6 +23,15 @@ public class SourceGenerator : ISourceGenerator
     {
         private const string NativeMethodsTxtAdditionalFileName = "NativeMethods.txt";
         private const string NativeMethodsJsonAdditionalFileName = "NativeMethods.json";
+
+        private static readonly DiagnosticDescriptor InternalError = new DiagnosticDescriptor(
+            "PInvoke000",
+            "CsWin32InternalError",
+            "An internal error occurred: {0}",
+            "Functionality",
+            DiagnosticSeverity.Error,
+            isEnabledByDefault: true);
+
         private static readonly DiagnosticDescriptor NoMatchingMethodOrType = new DiagnosticDescriptor(
             "PInvoke001",
             "No matching method or type found",
@@ -73,6 +82,14 @@ public class SourceGenerator : ISourceGenerator
             isEnabledByDefault: true,
             description: "Constants that are defined within enums should be generated by requesting the name of their declaring enum instead.");
 
+        private static readonly DiagnosticDescriptor CpuArchitectureIncompatibility = new DiagnosticDescriptor(
+            "PInvoke005",
+            "TargetSpecificCpuArchitecture",
+            "This API is only available when targeting a specific CPU architecture. AnyCPU cannot generate this API.",
+            "Functionality",
+            DiagnosticSeverity.Warning,
+            isEnabledByDefault: true);
+
         /// <inheritdoc/>
         public void Initialize(GeneratorInitializationContext context)
         {
@@ -141,31 +158,46 @@ public void Execute(GeneratorExecutionContext context)
 
                 name = name.Trim();
                 var location = Location.Create(nativeMethodsTxtFile.Path, line.Span, nativeMethodsTxt.Lines.GetLinePositionSpan(line.Span));
-                if (generator.BannedAPIs.TryGetValue(name, out string? reason))
+                try
                 {
-                    context.ReportDiagnostic(Diagnostic.Create(BannedApi, location, reason));
-                }
-                else if (name.EndsWith(".*", StringComparison.Ordinal))
-                {
-                    var moduleName = name.Substring(0, name.Length - 2);
-                    if (!generator.TryGenerateAllExternMethods(moduleName, context.CancellationToken))
+                    if (generator.BannedAPIs.TryGetValue(name, out string? reason))
                     {
-                        context.ReportDiagnostic(Diagnostic.Create(NoMethodsForModule, location, moduleName));
+                        context.ReportDiagnostic(Diagnostic.Create(BannedApi, location, reason));
                     }
-                }
-                else if (!generator.TryGenerate(name, context.CancellationToken))
-                {
-                    if (generator.TryGetEnumName(name, out string? declaringEnum))
+                    else if (name.EndsWith(".*", StringComparison.Ordinal))
+                    {
+                        var moduleName = name.Substring(0, name.Length - 2);
+                        if (!generator.TryGenerateAllExternMethods(moduleName, context.CancellationToken))
+                        {
+                            context.ReportDiagnostic(Diagnostic.Create(NoMethodsForModule, location, moduleName));
+                        }
+                    }
+                    else if (!generator.TryGenerate(name, context.CancellationToken))
                     {
-                        context.ReportDiagnostic(Diagnostic.Create(UseEnumValueDeclaringType, location, declaringEnum));
-                        if (!generator.TryGenerate(declaringEnum, context.CancellationToken))
+                        if (generator.TryGetEnumName(name, out string? declaringEnum))
                         {
-                            ReportNoMatch(location, declaringEnum);
+                            context.ReportDiagnostic(Diagnostic.Create(UseEnumValueDeclaringType, location, declaringEnum));
+                            if (!generator.TryGenerate(declaringEnum, context.CancellationToken))
+                            {
+                                ReportNoMatch(location, declaringEnum);
+                            }
                         }
+                        else
+                        {
+                            ReportNoMatch(location, name);
+                        }
+                    }
+                }
+                catch (GenerationFailedException ex)
+                {
+                    if (Generator.IsPlatformCompatibleException(ex))
+                    {
+                        context.ReportDiagnostic(Diagnostic.Create(CpuArchitectureIncompatibility, location));
                     }
                     else
                     {
-                        ReportNoMatch(location, name);
+                        // Build up a complete error message.
+                        context.ReportDiagnostic(Diagnostic.Create(InternalError, location, AssembleFullExceptionMessage(ex)));
                     }
                 }
             }
@@ -202,5 +234,25 @@ void ReportNoMatch(Location? location, string failedAttempt)
                 }
             }
         }
+
+        private static string AssembleFullExceptionMessage(Exception ex)
+        {
+            var sb = new StringBuilder();
+
+            Exception? inner = ex;
+            while (inner is object)
+            {
+                sb.Append(inner.Message);
+                if (sb.Length > 0 && sb[sb.Length - 1] != '.')
+                {
+                    sb.Append('.');
+                }
+
+                sb.Append(' ');
+                inner = inner.InnerException;
+            }
+
+            return sb.ToString();
+        }
     }
 }