Switch all diagnostics to errors

Make Compiles test check that all reported diagnostics are DLLIMPORTGEN

Add doc listing diagnostics reported by the P/Invoke source generator

DllImportGenerator/DllImportGenerator.UnitTests/Compiles.cs

@@ -161,6 +161,7 @@ public async Task ValidateSnippets_WithDiagnostics(string source)
 
             var newComp = TestUtils.RunGenerators(comp, out var generatorDiags, new Microsoft.Interop.DllImportGenerator());
             Assert.NotEmpty(generatorDiags);
+            Assert.All(generatorDiags, d => Assert.StartsWith(Microsoft.Interop.GeneratorDiagnostics.Ids.Prefix, d.Id));
 
             var newCompDiags = newComp.GetDiagnostics();
             Assert.Empty(newCompDiags);

DllImportGenerator/DllImportGenerator/GeneratorDiagnostics.cs

@@ -48,7 +48,7 @@ public static Diagnostic CreateDiagnostic(
     /// </summary>
     public class GeneratorDiagnostics
     {
-        private class Ids
+        public class Ids
         {
             public const string Prefix = "DLLIMPORTGEN";
             public const string TypeNotSupported = Prefix + "001";
@@ -63,7 +63,7 @@ private class Ids
                 GetResourceString(nameof(Resources.TypeNotSupportedTitle)),
                 GetResourceString(nameof(Resources.TypeNotSupportedMessageParameter)),
                 Category,
-                DiagnosticSeverity.Warning,
+                DiagnosticSeverity.Error,
                 isEnabledByDefault: true,
                 description: GetResourceString(Resources.TypeNotSupportedDescription));
 
@@ -73,7 +73,7 @@ private class Ids
                 GetResourceString(nameof(Resources.TypeNotSupportedTitle)),
                 GetResourceString(nameof(Resources.TypeNotSupportedMessageReturn)),
                 Category,
-                DiagnosticSeverity.Warning,
+                DiagnosticSeverity.Error,
                 isEnabledByDefault: true,
                 description: GetResourceString(Resources.TypeNotSupportedDescription));
 

DllImportGenerator/designs/Diagnostics.md

@@ -0,0 +1,39 @@
+# Generator Diagnostics
+
+For all [Roslyn diagnostics](https://docs.microsoft.com/dotnet/api/microsoft.codeanalysis.diagnostic) reported by the P/Invoke source generator:
+
+| Setting  | Value              |
+| -------- | ------------------ |
+| Category | DllImportGenerator |
+| Severity | Error              |
+| Enabled  | True               |
+
+The P/Invoke source generator emits the following diagnostics.
+
+## `DLLIMPORTGEN001`: Specified type is not supported by source-generated P/Invokes
+
+A method marked `GeneratedDllImport` has a parameter or return type that is not supported by source-generated P/Invokes.
+
+```C#
+// 'object' without any specific marshalling configuration
+[GeneratedDllImport("NativeLib")]
+public static partial void Method(object o);
+```
+
+## `DLLIMPORTGEN002`: Specified configuration is not supported by source-generated P/Invokes
+
+A method marked `GeneratedDllImport` has configuration that is not supported by source-generated P/Invokes. This may be configuration of the method itself or its parameter or return types.
+
+```C#
+// MarshalAs value that does not map to an UnmanagedType
+[GeneratedDllImport("NativeLib")]
+public static partial void Method([MarshalAs(1)] int i);
+
+// Unsupported field on MarshalAs (SafeArraySubType, SafeArrayUserDefinedSubType, IidParameterIndex)
+[GeneratedDllImport("NativeLib")]
+public static partial void Method([MarshalAs(UnmanagedType.SafeArray, SafeArraySubType = VarEnum.VT_BOOL)] bool[] bArr);
+
+// Unsupported combination of MarshalAs and type being marshalled
+[GeneratedDllImport("NativeLib")]
+public static partial void Method([MarshalAs(UnmanagedType.LPStr)] bool b);
+```