Disallow InlineArray attribute on a record struct type.

Closes dotnet#73504.

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -7983,4 +7983,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="IDS_FeatureAllowsRefStructConstraint" xml:space="preserve">
     <value>allows ref struct constraint</value>
   </data>
+  <data name="ERR_InlineArrayAttributeOnRecord" xml:space="preserve">
+    <value>Attribute 'System.Runtime.CompilerServices.InlineArray' cannot be applied to a record struct.</value>
+  </data>
 </root>

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -2338,6 +2338,8 @@ internal enum ErrorCode
 
         INF_IdentifierConflictWithContextualKeyword = 9258,
 
+        ERR_InlineArrayAttributeOnRecord = 9259,
+
         // Note: you will need to do the following after adding errors:
         //  1) Update ErrorFacts.IsBuildOnlyDiagnostic (src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs)
 

src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs

@@ -2456,6 +2456,7 @@ or ErrorCode.ERR_PartialPropertyTypeDifference
                 or ErrorCode.WRN_PartialPropertySignatureDifference
                 or ErrorCode.ERR_PartialPropertyRequiredDifference
                 or ErrorCode.INF_IdentifierConflictWithContextualKeyword
+                or ErrorCode.ERR_InlineArrayAttributeOnRecord
                     => false,
             };
 #pragma warning restore CS8524 // The switch expression does not handle some values of its input type (it is not exhaustive) involving an unnamed enum value.

src/Compilers/CSharp/Portable/Symbols/Source/SourceNamedTypeSymbol.cs

@@ -1212,6 +1212,10 @@ protected sealed override void DecodeWellKnownAttributeImpl(ref DecodeWellKnownA
                 {
                     diagnostics.Add(ErrorCode.ERR_AttributeOnBadSymbolType, arguments.AttributeSyntaxOpt.Name.Location, arguments.AttributeSyntaxOpt.GetErrorDisplayName(), "struct");
                 }
+                else if (IsRecordStruct)
+                {
+                    diagnostics.Add(ErrorCode.ERR_InlineArrayAttributeOnRecord, arguments.AttributeSyntaxOpt.Name.Location);
+                }
             }
             else
             {
@@ -1813,7 +1817,7 @@ protected override void AfterMembersCompletedChecks(BindingDiagnosticBag diagnos
                 }
             }
 
-            if (TypeKind == TypeKind.Struct && HasInlineArrayAttribute(out _))
+            if (TypeKind == TypeKind.Struct && !IsRecordStruct && HasInlineArrayAttribute(out _))
             {
                 if (Layout.Kind == LayoutKind.Explicit)
                 {

src/Compilers/CSharp/Test/Emit2/Semantics/InlineArrayTests.cs

@@ -1423,7 +1423,7 @@ struct Buffer
         }
 
         [Fact]
-        public void InlineArrayType_28()
+        public void InlineArrayType_28_Record()
         {
             var src = @"
 [System.Runtime.CompilerServices.InlineArray(10)]
@@ -1434,9 +1434,9 @@ record struct Buffer(int p)
 ";
             var comp = CreateCompilation(src, targetFramework: TargetFramework.Net80);
             comp.VerifyDiagnostics(
-                // (3,15): error CS9169: Inline array struct must declare one and only one instance field.
-                // record struct Buffer(int p)
-                Diagnostic(ErrorCode.ERR_InvalidInlineArrayFields, "Buffer").WithLocation(3, 15)
+                // (2,2): error CS9259: Attribute 'System.Runtime.CompilerServices.InlineArray' cannot be applied to a record struct.
+                // [System.Runtime.CompilerServices.InlineArray(10)]
+                Diagnostic(ErrorCode.ERR_InlineArrayAttributeOnRecord, "System.Runtime.CompilerServices.InlineArray").WithLocation(2, 2)
                 );
 
             var buffer = comp.GlobalNamespace.GetTypeMember("Buffer");
@@ -2188,6 +2188,79 @@ static void Main()
                 );
         }
 
+        [Fact]
+        public void InlineArrayType_52_Record()
+        {
+            var src = @"
+[System.Runtime.CompilerServices.InlineArray(10)]
+record struct Buffer(int p1, int p2)
+{
+}
+";
+            var comp = CreateCompilation(src, targetFramework: TargetFramework.Net80);
+            comp.VerifyDiagnostics(
+                // (2,2): error CS9259: Attribute 'System.Runtime.CompilerServices.InlineArray' cannot be applied to a record struct.
+                // [System.Runtime.CompilerServices.InlineArray(10)]
+                Diagnostic(ErrorCode.ERR_InlineArrayAttributeOnRecord, "System.Runtime.CompilerServices.InlineArray").WithLocation(2, 2)
+                );
+
+            var buffer = comp.GlobalNamespace.GetTypeMember("Buffer");
+
+            Assert.True(buffer.HasInlineArrayAttribute(out int length));
+            Assert.Equal(10, length);
+            Assert.Null(buffer.TryGetInlineArrayElementField());
+        }
+
+        [Theory]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        public void InlineArrayType_53_Record(int size)
+        {
+            var src = @"
+[System.Runtime.CompilerServices.InlineArray(" + size + @")]
+record struct Buffer()
+{
+    private int _element0;
+}
+";
+            var comp = CreateCompilation(src, targetFramework: TargetFramework.Net80);
+            comp.VerifyDiagnostics(
+                // (2,2): error CS9259: Attribute 'System.Runtime.CompilerServices.InlineArray' cannot be applied to a record struct.
+                // [System.Runtime.CompilerServices.InlineArray(1)]
+                Diagnostic(ErrorCode.ERR_InlineArrayAttributeOnRecord, "System.Runtime.CompilerServices.InlineArray").WithLocation(2, 2)
+                );
+
+            var buffer = comp.GlobalNamespace.GetTypeMember("Buffer");
+
+            Assert.True(buffer.HasInlineArrayAttribute(out int length));
+            Assert.Equal(size, length);
+            Assert.Equal(SpecialType.System_Int32, buffer.TryGetInlineArrayElementField().Type.SpecialType);
+        }
+
+        [Fact]
+        public void InlineArrayType_54_Record()
+        {
+            var src = @"
+[System.Runtime.CompilerServices.InlineArray(10)]
+record struct Buffer()
+{
+}
+";
+            var comp = CreateCompilation(src, targetFramework: TargetFramework.Net80);
+            comp.VerifyDiagnostics(
+                // (2,2): error CS9259: Attribute 'System.Runtime.CompilerServices.InlineArray' cannot be applied to a record struct.
+                // [System.Runtime.CompilerServices.InlineArray(10)]
+                Diagnostic(ErrorCode.ERR_InlineArrayAttributeOnRecord, "System.Runtime.CompilerServices.InlineArray").WithLocation(2, 2)
+                );
+
+            var buffer = comp.GlobalNamespace.GetTypeMember("Buffer");
+
+            Assert.True(buffer.HasInlineArrayAttribute(out int length));
+            Assert.Equal(10, length);
+            Assert.Null(buffer.TryGetInlineArrayElementField());
+        }
+
         [Fact]
         public void Access_ArgumentType_01()
         {