From 016f71d08dbc2896f6de1721612cade25892b47b Mon Sep 17 00:00:00 2001
From: Elinor Fung <elfung@microsoft.com>
Date: Fri, 9 Oct 2020 14:10:19 -0700
Subject: [PATCH] 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.UnitTests/Compiles.cs  |  1 +
 .../GeneratorDiagnostics.cs                   |  6 +--
 DllImportGenerator/designs/Diagnostics.md     | 39 +++++++++++++++++++
 3 files changed, 43 insertions(+), 3 deletions(-)
 create mode 100644 DllImportGenerator/designs/Diagnostics.md

diff --git a/DllImportGenerator/DllImportGenerator.UnitTests/Compiles.cs b/DllImportGenerator/DllImportGenerator.UnitTests/Compiles.cs
index ab1b7aff1032..815db781816b 100644
--- a/DllImportGenerator/DllImportGenerator.UnitTests/Compiles.cs
+++ b/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);
diff --git a/DllImportGenerator/DllImportGenerator/GeneratorDiagnostics.cs b/DllImportGenerator/DllImportGenerator/GeneratorDiagnostics.cs
index e3f7a39a9543..17657fe4eaf5 100644
--- a/DllImportGenerator/DllImportGenerator/GeneratorDiagnostics.cs
+++ b/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));
 
diff --git a/DllImportGenerator/designs/Diagnostics.md b/DllImportGenerator/designs/Diagnostics.md
new file mode 100644
index 000000000000..d69d633022b0
--- /dev/null
+++ b/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);
+```
\ No newline at end of file