[Syntax] Add a comment explaining the pointer keys in std::map<Token*, ...>. NFC

1 files changed, 2 insertions, 0 deletions

diff --git a/clang/lib/Tooling/Syntax/BuildTree.cpp b/clang/lib/Tooling/Syntax/BuildTree.cpp
index b36b8e0..22cdb89 100644
--- a/clang/lib/Tooling/Syntax/BuildTree.cpp
+++ b/clang/lib/Tooling/Syntax/BuildTree.cpp
@@ -209,6 +209,8 @@ private:
     };
 
     /// Maps from the start token to a subtree starting at that token.
+    /// Keys in the map are pointers into the array of expanded tokens, so
+    /// pointer order corresponds to the order of preprocessor tokens.
     /// FIXME: storing the end tokens is redundant.
     /// FIXME: the key of a map is redundant, it is also stored in NodeForRange.
     std::map<const syntax::Token *, NodeAndRole> Trees;