Add snippet support for component completion with EditorRequired attributes (#12325)

- [x] Understand the current completion system and how TagHelper element
completion works
- [x] Modify RazorCompletionItem.CreateTagHelperElement to support
snippet mode
- [x] Update GetElementCompletions in TagHelperCompletionProvider to
detect EditorRequired attributes
- [x] Build snippet text with placeholders for EditorRequired properties
- [x] Add comprehensive tests for the new snippet functionality
- [x] Validate the changes work correctly
- [x] Address PR feedback:
- Changed to add a separate completion item for snippets (with "..."
suffix) instead of modifying the existing item
- Always add quotes in snippets (removed autoInsertAttributeQuotes
parameter)
  - Use pooled StringBuilder instead of regular StringBuilder
  - Added test in CohostDocumentCompletionEndpointTest.cs
  - Simplified Cohost test to use VerifyCompletionListAsync helper
- Optimized component tag helper lookup to use first Component kind tag
helper only
- [x] Merged main into branch (test files moved to VS Code project)
- [x] Fixed test failure - snippet items don't need resolve, they
already have complete insertText
- [x] Updated snippet display text to "{displayText} (and req'd
attributes...)" for better clarity
- [x] Simplified test to use VerifyCompletionListAsync helper with
verifySnippetItem callback
- [x] Optimized to avoid .Any() and .ToImmutableArray() allocation by
changing method to accept IEnumerable
- [x] Added localized resource string for component completion label
- [x] Updated tests to use SR resource for consistent labeling
- [x] Extracted snippet completion logic to
AddCompletionItemWithRequiredAttributesSnippet method
- [x] Inverted if statement for early exit and pass descriptionInfo from
calling method
- [x] Merged latest main and resolved conflicts - both
ComponentWithEditorRequiredAttributes and new Blazor data attribute
tests now coexist
- [x] Added comment to SR.resx explaining "req'd" abbreviation for
localization

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<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>Component completion snippet</issue_title>
> <issue_description>Noticed today watching someone use the Razor
editor: For components that have one or more properties that are
`[EditorRequired]`, we could do completion as a snippet, that includes
the attributes for each required property (similar to how drag and drop
will create attributes for them) and either puts the caret in the first
one, or even puts placeholders in each and lets the user tab between
them.</issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>

Fixes #6980

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Author: davidwengier

.github/workflows/copilot-setup-steps.yml

@@ -40,6 +40,11 @@ jobs:
         # Use restore script, but don't fail on errors so Copilot can still attempt to work
         run: ./restore.sh
 
+      # Activate the private .NET install. Hopefully this resolves firewall issues when using dotnet build/test
+      - name: Activate
+        continue-on-error: true
+        run: source ./activate.sh
+
       # Diagnostics in the log
       - name: Show .NET info
         run: dotnet --info

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/RazorCompletionItem.cs

@@ -87,8 +87,9 @@ public static RazorCompletionItem CreateTagHelperElement(
         string displayText, string insertText,
         AggregateBoundElementDescription descriptionInfo,
         ImmutableArray<RazorCommitCharacter> commitCharacters,
+        bool isSnippet = false,
         TextEdit[]? additionalTextEdits = null)
-        => new(RazorCompletionItemKind.TagHelperElement, displayText, insertText, sortText: null, descriptionInfo, commitCharacters, isSnippet: false, additionalTextEdits);
+        => new(RazorCompletionItemKind.TagHelperElement, displayText, insertText, sortText: null, descriptionInfo, commitCharacters, isSnippet, additionalTextEdits);
 
     public static RazorCompletionItem CreateTagHelperAttribute(
         string displayText, string insertText, string? sortText,

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/TagHelperCompletionProvider.cs

@@ -231,13 +231,24 @@ private ImmutableArray<RazorCompletionItem> GetElementCompletions(
         {
             var descriptionInfo = new AggregateBoundElementDescription(tagHelpers.SelectAsArray(BoundElementDescriptionInfo.From));
 
+            // Always add the regular completion item
             var razorCompletionItem = RazorCompletionItem.CreateTagHelperElement(
                 displayText: displayText,
                 insertText: displayText,
                 descriptionInfo,
-                commitCharacters: commitChars);
+                commitCharacters: commitChars,
+                isSnippet: false);
 
             completionItems.Add(razorCompletionItem);
+
+            AddCompletionItemWithRequiredAttributesSnippet(
+                ref completionItems.AsRef(),
+                context,
+                tagHelpers,
+                displayText,
+                descriptionInfo,
+                commitChars);
+
             AddCompletionItemWithUsingDirective(ref completionItems.AsRef(), context, commitChars, displayText, descriptionInfo);
         }
 
@@ -307,6 +318,79 @@ private static ImmutableArray<RazorCommitCharacter> ResolveAttributeCommitCharac
         };
     }
 
+    private static void AddCompletionItemWithRequiredAttributesSnippet(
+        ref PooledArrayBuilder<RazorCompletionItem> completionItems,
+        RazorCompletionContext context,
+        IEnumerable<TagHelperDescriptor> tagHelpers,
+        string displayText,
+        AggregateBoundElementDescription descriptionInfo,
+        ImmutableArray<RazorCommitCharacter> commitChars)
+    {
+        // If snippets are not supported, exit early
+        if (!context.Options.SnippetsSupported)
+        {
+            return;
+        }
+
+        if (TryGetEditorRequiredAttributesSnippet(tagHelpers, displayText, out var snippetText))
+        {
+            var snippetCompletionItem = RazorCompletionItem.CreateTagHelperElement(
+                displayText: SR.FormatComponentCompletionWithRequiredAttributesLabel(displayText),
+                insertText: snippetText,
+                descriptionInfo: descriptionInfo,
+                commitCharacters: commitChars,
+                isSnippet: true);
+
+            completionItems.Add(snippetCompletionItem);
+        }
+    }
+
+    private static bool TryGetEditorRequiredAttributesSnippet(
+        IEnumerable<TagHelperDescriptor> tagHelpers,
+        string tagName,
+        [NotNullWhen(true)] out string? snippetText)
+    {
+        // For components, there should only be one tag helper descriptor per component name
+        // Get EditorRequired attributes from the first component tag helper
+        var componentTagHelper = tagHelpers.FirstOrDefault(th => th.Kind == TagHelperKind.Component);
+        if (componentTagHelper is null)
+        {
+            snippetText = null;
+            return false;
+        }
+
+        var requiredAttributes = componentTagHelper.EditorRequiredAttributes;
+        if (requiredAttributes.Length == 0)
+        {
+            snippetText = null;
+            return false;
+        }
+
+        // Build snippet with placeholders for each required attribute
+        using var _ = StringBuilderPool.GetPooledObject(out var builder);
+        builder.Append(tagName);
+
+        var tabStopIndex = 1;
+        foreach (var attribute in requiredAttributes)
+        {
+            builder.Append(' ');
+            builder.Append(attribute.Name);
+            builder.Append("=\"$");
+            builder.Append(tabStopIndex);
+            builder.Append('"');
+
+            tabStopIndex++;
+        }
+
+        // Add final tab stop for the element content
+        builder.Append(">$0</");
+        builder.Append(tagName);
+        builder.Append('>');
+
+        snippetText = builder.ToString();
+        return true;
+    }
+
     private enum AttributeContext
     {
         Indexer,

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Resources/SR.resx

@@ -223,4 +223,8 @@
   <data name="ExtractTo_Css_Title" xml:space="preserve">
     <value>Extract to {0}.css</value>
   </data>
+  <data name="ComponentCompletionWithRequiredAttributesLabel" xml:space="preserve">
+    <value>{0} (and req'd attributes...)</value>
+    <comment>The term "req'd" is an abbreviation for "required"</comment>
+  </data>
 </root>