Work around metadata-only PDB emit failures

src/Basic.CompilerLog.UnitTests/CompilationDataTests.cs

@@ -2,6 +2,7 @@
 using Basic.CompilerLog.Util;
 using Basic.CompilerLog.Util.Impl;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Emit;
 using Microsoft.Testing.Platform.Extensions.Messages;
 using Xunit;
 
@@ -82,6 +83,28 @@ public void EmitToMemoryCombinations()
         });
     }
 
+    /// <summary>
+    /// Covers <see href="https://github.com/dotnet/roslyn/issues/78721"/> while the fix in
+    /// <see href="https://github.com/dotnet/roslyn/pull/85028"/> is not yet available in our Roslyn package.
+    /// </summary>
+    [Fact]
+    public void EmitToMemoryMetadataOnlyWithPdbPath()
+    {
+        RunInContext(Fixture.ClassLib.Value.CompilerLogPath, static (testOutputHelper, filePath, cancellationToken) =>
+        {
+            using var reader = CompilerLogReader.Create(filePath);
+            var data = reader.ReadCompilationData(0);
+            var emitOptions = data.EmitOptions
+                .WithEmitMetadataOnly(true)
+                .WithDebugInformationFormat(DebugInformationFormat.Embedded)
+                .WithPdbFilePath("test.pdb");
+
+            var exception = Assert.Throws<ArgumentException>(
+                () => data.EmitToMemory(EmitFlags.MetadataOnly, emitOptions, cancellationToken));
+            Assert.Equal("metadataPEStream", exception.ParamName);
+        });
+    }
+
     [Fact]
     public void EmitToMemoryRefOnly()
     {

src/Basic.CompilerLog.Util/CompilerLogReader.cs

@@ -374,6 +374,7 @@ public IReadOnlyCollection<string> ReadArguments(CompilerCall compilerCall)
         CompilationDataPack dataPack)
     {
         var emitOptions = MessagePackUtil.CreateEmitOptions(GetContentPack<EmitOptionsPack>(pack.EmitOptionsHash));
+        emitOptions = ApplyMetadataOnlyEmitWorkaround(emitOptions);
         ParseOptions parseOptions;
         CompilationOptions compilationOptions;
         if (pack.IsCSharp)
@@ -396,6 +397,25 @@ public IReadOnlyCollection<string> ReadArguments(CompilerCall compilerCall)
         compilationOptions = MaterializeCryptoKeyFile(dataPack, compilationOptions);
         return (emitOptions, parseOptions, compilationOptions);
 
+        EmitOptions ApplyMetadataOnlyEmitWorkaround(EmitOptions emitOptions)
+        {
+            // Metadata-only output cannot have an associated PDB. Current Roslyn can retain the PDB path,
+            // emit a CodeView entry, or reject embedded debug information. Work around dotnet/roslyn#85028
+            // until a Roslyn package containing the fix is available.
+            if (!emitOptions.EmitMetadataOnly)
+            {
+                return emitOptions;
+            }
+
+            emitOptions = emitOptions.WithPdbFilePath(null!);
+            if (emitOptions.DebugInformationFormat == DebugInformationFormat.Embedded)
+            {
+                emitOptions = emitOptions.WithDebugInformationFormat(DebugInformationFormat.PortablePdb);
+            }
+
+            return emitOptions;
+        }
+
         // This method will materialize the crypto key file to the location specified by the path mapping util. This
         // is the rare case where reading compilation information will cause a file to be written to disk. It's the
         // rare case where the compiler reads directly from disk at binding vs. pre-reading at Compilation creation