[clang] [clang][NFC] Add documentation for `CastExpr::path()`. (PR #85623)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (martinboehme)

<details>
<summary>Changes</summary>

This didn't have any documentation, so I had to do some experimenting in
godbolt when I used this in https://github.com/llvm/llvm-project/pull/84138,
and my reviewer later also had some
[questions](https://github.com/llvm/llvm-project/pull/84138#discussion_r1524855434)
about this, so I figured it would be worth adding documentation.


---
Full diff: https://github.com/llvm/llvm-project/pull/85623.diff


1 Files Affected:

- (modified) clang/include/clang/AST/Expr.h (+9) 


``````````diff
diff --git a/clang/include/clang/AST/Expr.h b/clang/include/clang/AST/Expr.h
index 446bec4081e869..8c4db4828477d0 100644
--- a/clang/include/clang/AST/Expr.h
+++ b/clang/include/clang/AST/Expr.h
@@ -3552,6 +3552,15 @@ class CastExpr : public Expr {
   /// function that it invokes.
   NamedDecl *getConversionFunction() const;
 
+  /// Path through the class hierarchy taken by a `DerivedToBase` or
+  /// `UncheckedDerivedToBase` cast. For each derived-to-base edge in the path,
+  /// the path contains a `CXXBaseSpecifier` for the base class of that edge;
+  /// the entries are ordered from derived class to base class.
+  ///
+  /// For example, given classes `Base`, `Intermediate : public Base` and
+  /// `Derived : public Intermediate`, the path for a cast from `Derived *` to
+  /// `Base *` contains two entries: One for `Intermediate`, and one for `Base`,
+  /// in that order.
   typedef CXXBaseSpecifier **path_iterator;
   typedef const CXXBaseSpecifier *const *path_const_iterator;
   bool path_empty() const { return path_size() == 0; }

``````````

</details>


https://github.com/llvm/llvm-project/pull/85623