Add cohosting Hover test for component attribute (#11171)

Even though component attributes look like HTML they map to generated
C#. In this case, Hover prefers C# over HTML and requests hover data
from Roslyn. This adds a test for that scenario.

Author: DustinCampbell

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

@@ -40,7 +40,7 @@ await VerifyHoverAsync(code, async (hover, document) =>
                 Container(
                     Container(
                         Image,
-                        ClassifiedText(
+                        ClassifiedText( // Microsoft.AspNetCore.Components.Web.PageTitle
                             Text("Microsoft"),
                             Punctuation("."),
                             Text("AspNetCore"),
@@ -67,6 +67,7 @@ public async Task Html()
             }
             """;
 
+        // This simply verifies that Hover will call into HTML.
         var htmlResponse = new VSInternalHover();
 
         await VerifyHoverAsync(code, htmlResponse, h => Assert.Same(htmlResponse, h));
@@ -94,7 +95,7 @@ await VerifyHoverAsync(code, async (hover, document) =>
                 Container(
                     Container(
                         Image,
-                        ClassifiedText(
+                        ClassifiedText( // (local variable) string myVariable
                             Punctuation("("),
                             Text("local variable"),
                             Punctuation(")"),
@@ -105,6 +106,45 @@ await VerifyHoverAsync(code, async (hover, document) =>
         });
     }
 
+    [Fact]
+    public async Task ComponentAttribute()
+    {
+        // Component attributes are within HTML but actually map to C#.
+        // In this situation, Hover prefers treating the position as C# and calls
+        // Roslyn rather than HTML.
+
+        TestCode code = """
+            <EditForm [|Form$$Name|]="Hello" />
+            """;
+
+        await VerifyHoverAsync(code, async (hover, document) =>
+        {
+            await hover.VerifyRangeAsync(code.Span, document);
+
+            hover.VerifyRawContent(
+                Container(
+                    Container(
+                        Image,
+                        ClassifiedText( // string? EditForm.FormName { get; set; }
+                            Keyword("string"),
+                            Punctuation("?"),
+                            WhiteSpace(" "),
+                            ClassName("EditForm"),
+                            Punctuation("."),
+                            PropertyName("FormName"),
+                            WhiteSpace(" "),
+                            Punctuation("{"),
+                            WhiteSpace(" "),
+                            Keyword("get"),
+                            Punctuation(";"),
+                            WhiteSpace(" "),
+                            Keyword("set"),
+                            Punctuation(";"),
+                            WhiteSpace(" "),
+                            Punctuation("}")))));
+        });
+    }
+
     private async Task VerifyHoverAsync(TestCode input, Func<RoslynHover, TextDocument, Task> verifyHover)
     {
         var document = await CreateProjectAndRazorDocumentAsync(input.Text);

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

@@ -79,12 +79,18 @@ public static Action<ClassifiedTextRun> Run(string text, string? classificationT
             Assert.Equal(text, run.Text);
         };
 
+    public static Action<ClassifiedTextRun> ClassName (string text)
+        => Run(text, ClassificationTypeNames.ClassName);
+
     public static Action<ClassifiedTextRun> Keyword(string text)
         => Run(text, ClassificationTypeNames.Keyword);
 
     public static Action<ClassifiedTextRun> LocalName(string text)
         => Run(text, ClassificationTypeNames.LocalName);
 
+    public static Action<ClassifiedTextRun> PropertyName(string text)
+        => Run(text, ClassificationTypeNames.PropertyName);
+
     public static Action<ClassifiedTextRun> Punctuation(string text)
         => Run(text, ClassificationTypeNames.Punctuation);