[clang] [Clang][Comments] Support for parsing headers in Doxygen \par commands (PR #91100)

[via cfe-commits]

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@@ -149,6 +149,63 @@ class TextTokenRetokenizer {
     addToken();
   }
 
+  /// Check if this line starts with @par or \par
+  bool startsWithParCommand() {
+    unsigned Offset = 1;
+
+    /// Skip all whitespace characters at the beginning.
+    /// This needs to backtrack because Pos has already advanced past the
+    /// actual \par or @par command by the time this function is called.
+    while (isWhitespace(*(Pos.BufferPtr - Offset)))
+      Offset++;
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hdoc wrote:

In this case we actually have to read the buffer backwards to find the `@par`, past `Pos.BufferStart` so it's a bit inconvenient to construct the `StringRef` which starts at some unknown position before `Pos.BufferStart`. In theory someone could have put 400 spaces between `@par` and the comment text, and we'd have to accommodate that when constructing the `StringRef`. 

I think the solution as it's written right now handles that well enough. I could make it count spaces or look up the previous token containing the `@par` and compute the correct StringRef for it, but I think this is good enough.

https://github.com/llvm/llvm-project/pull/91100