Ignore embedded debug format for metadata-only emit

src/Compilers/CSharp/Test/CommandLine/CommandLineTests.cs

@@ -12044,6 +12044,30 @@ private struct S
             CleanupAllGeneratedFiles(dir.Path);
         }
 
+        [Fact]
+        public void RefOnly_EmbeddedDebugInformation()
+        {
+            var dir = Temp.CreateDirectory();
+            var src = dir.CreateFile("a.cs");
+            src.WriteAllText("public class C { }");
+
+            var outWriter = new StringWriter(CultureInfo.InvariantCulture);
+            var csc = CreateCSharpCompiler(null, dir.Path,
+                new[] { "/nologo", "/target:library", "/out:a.dll", "/refonly", "/debug:embedded", "/deterministic", "a.cs" });
+
+            Assert.Equal(0, csc.Run(outWriter));
+            Assert.Equal("", outWriter.ToString());
+
+            using (var peReader = new PEReader(File.OpenRead(Path.Combine(dir.Path, "a.dll"))))
+            {
+                AssertEx.Equal(
+                    new[] { DebugDirectoryEntryType.Reproducible },
+                    peReader.ReadDebugDirectory().Select(entry => entry.Type));
+            }
+
+            CleanupAllGeneratedFiles(dir.Path);
+        }
+
         [Fact]
         public void CompilingCodeWithInvalidPreProcessorSymbolsShouldProvideDiagnostics()
         {

src/Compilers/CSharp/Test/Emit/Emit/CompilationEmitTests.cs

@@ -2709,16 +2709,22 @@ void verifyEmbeddedDebugInfo(MemoryStream stream, DebugDirectoryEntryType[] expe
         }
 
         [Fact]
-        public void EmitMetadataOnly_DisallowEmbeddingPdb()
+        public void EmitMetadataOnly_IgnoreEmbeddedPdb()
         {
             CSharpCompilation comp = CreateEmptyCompilation("", references: new[] { MscorlibRef },
-                options: TestOptions.DebugDll);
+                options: TestOptions.DebugDll.WithDeterministic(true));
 
             using (var output = new MemoryStream())
             {
-                Assert.Throws<ArgumentException>(() => comp.Emit(output,
+                var result = comp.Emit(output,
                     options: EmitOptions.Default.WithEmitMetadataOnly(true)
-                        .WithDebugInformationFormat(DebugInformationFormat.Embedded)));
+                        .WithDebugInformationFormat(DebugInformationFormat.Embedded));
+
+                Assert.True(result.Success);
+                using var peReader = new PEReader(output.ToImmutable());
+                AssertEx.Equal(
+                    new[] { DebugDirectoryEntryType.Reproducible },
+                    peReader.ReadDebugDirectory().Select(entry => entry.Type));
             }
         }
 

src/Compilers/Core/Portable/CodeAnalysisResources.resx

@@ -312,9 +312,6 @@
   <data name="IncludingPrivateMembersUnexpectedWhenEmittingToMetadataPeStream" xml:space="preserve">
     <value>Including private members should not be used when emitting to the secondary assembly output.</value>
   </data>
-  <data name="EmbeddingPdbUnexpectedWhenEmittingMetadata" xml:space="preserve">
-    <value>Embedding PDB is not allowed when emitting metadata.</value>
-  </data>
   <data name="CannotTargetNetModuleWhenEmittingRefAssembly" xml:space="preserve">
     <value>Cannot target net module when emitting ref assembly.</value>
   </data>

src/Compilers/Core/Portable/Compilation/Compilation.cs

@@ -2887,12 +2887,6 @@ internal EmitResult Emit(
                 options = options.WithIncludePrivateMembers(true);
             }
 
-            if (options?.DebugInformationFormat == DebugInformationFormat.Embedded &&
-                options?.EmitMetadataOnly == true)
-            {
-                throw new ArgumentException(CodeAnalysisResources.EmbeddingPdbUnexpectedWhenEmittingMetadata, nameof(metadataPEStream));
-            }
-
             if (this.Options.OutputKind == OutputKind.NetModule)
             {
                 if (metadataPEStream != null)
@@ -3274,7 +3268,12 @@ internal bool SerializeToPeStream(
 
             string? pePdbFilePath = emitOptions.PdbFilePath;
 
-            if (moduleBeingBuilt.DebugInformationFormat == DebugInformationFormat.Embedded || pdbStreamProvider != null)
+            if (emitOptions.EmitMetadataOnly)
+            {
+                // Metadata-only output has no associated PDB. Clear the path so the PE writer doesn't emit a CodeView entry.
+                pePdbFilePath = null;
+            }
+            else if (moduleBeingBuilt.DebugInformationFormat == DebugInformationFormat.Embedded || pdbStreamProvider != null)
             {
                 pePdbFilePath = pePdbFilePath ?? FileNameUtilities.ChangeExtension(SourceModule.Name, "pdb");
             }