Filter our html diagnostics when a tag helper attribute spans multiple lines

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Diagnostics/RazorTranslateDiagnosticsService.cs

@@ -453,13 +453,19 @@ private static bool InAttributeContainingCSharp(
 
         if (markupAttributeValue is not null)
         {
-            if (!processedAttributes.TryGetValue(markupAttributeValue.Span, out var doesAttributeContainNonMarkup))
+            if (!processedAttributes.TryGetValue(markupAttributeValue.Span, out var shouldFilterDiagnostic))
             {
-                doesAttributeContainNonMarkup = CheckIfAttributeContainsNonMarkupNodes(markupAttributeValue);
-                processedAttributes.Add(markupAttributeValue.Span, doesAttributeContainNonMarkup);
+                // If a component attribute is spread across multiple lines, it's not valid Html so the Html server can't be expected to reason
+                // about the contents correctly
+                shouldFilterDiagnostic = markupAttributeValue is MarkupTagHelperAttributeValueSyntax &&
+                    markupAttributeValue.GetLinePositionSpan(syntaxTree.Source).SpansMultipleLines();
+
+                // Similarly, if the attribute value contains non-markup, the Html could report false positives
+                shouldFilterDiagnostic |= CheckIfAttributeContainsNonMarkupNodes(markupAttributeValue);
+                processedAttributes.Add(markupAttributeValue.Span, shouldFilterDiagnostic);
             }
 
-            return doesAttributeContainNonMarkup;
+            return shouldFilterDiagnostic;
         }
 
         return false;

src/Razor/test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Cohost/CohostDocumentPullDiagnosticsTest.cs

@@ -420,6 +420,58 @@ public Task FilterPropertyNameInCss()
             }]);
     }
 
+    [Fact]
+    public Task FilterFromMultilineComponentAttributes()
+    {
+        var firstLine = "Hello this is a";
+        TestCode input = $$"""
+            <File1 Title="{{firstLine}}
+                          multiline attribute" />
+
+            @code
+            {
+                [Parameter]
+                public string Title { get; set; }
+            }
+            """;
+
+        return VerifyDiagnosticsAsync(input,
+            htmlResponse: [new VSInternalDiagnosticReport
+            {
+                Diagnostics =
+                [
+                    new LspDiagnostic
+                    {
+                        Code = HtmlErrorCodes.MismatchedAttributeQuotesErrorCode,
+                        Range = SourceText.From(input.Text).GetRange(new TextSpan(input.Text.IndexOf(firstLine), firstLine.Length))
+                    },
+                ]
+            }]);
+    }
+
+    [Fact]
+    public Task DontFilterFromMultilineHtmlAttributes()
+    {
+        var firstLine = "Hello this is a";
+        TestCode input = $$"""
+            <div class="{|HTML0005:{{firstLine}}|}
+                        multiline attribute" />
+            """;
+
+        return VerifyDiagnosticsAsync(input,
+            htmlResponse: [new VSInternalDiagnosticReport
+            {
+                Diagnostics =
+                [
+                    new LspDiagnostic
+                    {
+                        Code = HtmlErrorCodes.MismatchedAttributeQuotesErrorCode,
+                        Range = SourceText.From(input.Text).GetRange(new TextSpan(input.Text.IndexOf(firstLine), firstLine.Length))
+                    },
+                ]
+            }]);
+    }
+
     [Theory]
     [InlineData("", "\"")]
     [InlineData("", "'")]