[clang] [clang-transformer] Allow stencils to read from system headers. (PR #66480)

[Yitzhak Mandelbaum via cfe-commits]

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@@ -91,6 +91,10 @@ StringRef getExtendedText(const T &Node, tok::TokenKind Next,
 llvm::Error validateEditRange(const CharSourceRange &Range,
                               const SourceManager &SM);
 
+/// Determines whether \p Range is one that can be read from.
+llvm::Error validateRange(const CharSourceRange &Range, const SourceManager &SM,
+                          bool AllowSystemHeaders);
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ymand wrote:

Please explain `AllowSystemHeaders` in the comments. May not be totally obvious.

https://github.com/llvm/llvm-project/pull/66480