Fix SyntaxNode.Ancestors() to work correctly with structured trivia

[Copilot]

Fix: DocumentationCommentTriviaSyntax.Ancestors() returns empty collection

Problem

• Ancestors(ascendOutOfTrivia: true) on DocumentationCommentTriviaSyntax returned no ancestors
• AncestorsAndSelf(ascendOutOfTrivia: true) correctly returned all ancestors including self

Root Cause

The Ancestors method in SyntaxNode.cs was using this.Parent directly, which is null for structured trivia nodes. It should use the GetParent helper method (like AncestorsAndSelf does) which knows how to ascend out of structured trivia when ascendOutOfTrivia is true.

Solution

Changed Ancestors to use GetParent(this, ascendOutOfTrivia) instead of just this.Parent.

Changes Made

• Analyze the issue and identify root cause
• Fix the Ancestors method in SyntaxNode.cs
• Add test case for DocumentationCommentTriviaSyntax.Ancestors()
• Add test case for DefineDirectiveTriviaSyntax (another structured trivia type)
• Build and run tests to verify fix (all 197 SyntaxNodeTests pass)
• Run code review and address comments
• Add clarifying comment about directive trivia test behavior
• Add WorkItem attributes and use raw string literals

Testing

• All existing 197 tests in SyntaxNodeTests pass
• Added 2 new tests specifically for structured trivia:
  • TestAncestorsOfDocumentationCommentTrivia - tests doc comment trivia
  • TestAncestorsOfDirectiveTrivia - tests preprocessor directive trivia

Fixes #46964

Original prompt

---

This section details on the original issue you should resolve

<issue_title>'DocumentationCommentTriviaSyntax.Ancestors(true)' does not return any ancestors but 'AncestorsAndSelf(true)' does</issue_title>
<issue_description>Version Used:
3.6

Steps to Reproduce:

1. Get the DocumentationCommentTriviaSyntax that represents the comment in following snippet:

public class TestMe
{
    /// <summary>
    /// Some summary.
    /// </summary>
    /// <value>
    /// Some value.
    /// </value>
    private int i;
}

2. Invoke SyntaxNode.Ancestors() and SyntaxNode.AncestorsAndSelf(true) on the DocumentationCommentTriviaSyntax.
3. Compare the results and find out that Ancestors() does neither return the FieldDeclarationSyntax, nor the ClassDeclarationSyntax, nor the CompilationUnitSyntax.
   In contrast, AncestorsAndSelf() returns them all.

Expected Behavior:
Invoking SyntaxNode.Ancestors(true) on a DocumentationCommentTriviaSyntax returns all ancestors, similar to SyntaxNode.AncestorsAndSelf(true), except the trivia (no self).

Actual Behavior:
SyntaxNode.Ancestors(true) invoked on a DocumentationCommentTriviaSyntax returns no ancestors.

SyntaxNode.AncestorsAndSelf(true) invoked on the same DocumentationCommentTriviaSyntax not only returns the trivia as expected, but also all the other ancestors that SyntaxNode.Ancestors(true) is missing to return.</issue_description>

<agent_instructions>See conversation for likely fix.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@CyrusNajmabadi ```c# public IEnumerable Ancestors(bool ascendOutOfTrivia = true) { return this.Parent? .AncestorsAndSelf(ascendOutOfTrivia) ?? SpecializedCollections.EmptyEnumerable(); } ```

should likely be updated to be:

        public IEnumerable<SyntaxNode> Ancestors(bool ascendOutOfTrivia = true)
        {
            return GetParent(this, ascendOutOfTrivia)?
                .AncestorsAndSelf(ascendOutOfTrivia) ??
                SpecializedCollections.EmptyEnumerable<SyntaxNode>();
        }
```</body></comment_new>
</comments>

Fixes #46964

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[CyrusNajmabadi]

@copilot add a WorkItem attribute. And use a raw string literal for the test. This applies to all tests you added.

[Copilot]

Done in commit e8d5c67. Added [WorkItem("https://github.com/dotnet/roslyn/issues/46964")] attribute to both tests and converted the verbatim strings to raw string literals.

[CyrusNajmabadi]

@dotnet/roslyn-compiler ptal.