[clang] [Clang] [C++26] Iterating expansion statements using string injection (PR #208877)

[Ambrose Leeb via cfe-commits]

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@@ -855,6 +855,31 @@ enum AttrName { Target, TargetClones, TargetVersion };
 
 void inferNoReturnAttr(Sema &S, Decl *D);
 
+namespace sema {
+/// Proxy class to parse a list of tokens and/or code strings.
+///
+/// This is really intended to provide access to 'Parser' without making the
+/// Sema library depend on the Parser library. We sometimes may want to generate
+/// implicit AST nodes, but doing so by calling various ActOnXY() functions in
+/// hopefully the right order and with the right arguments is both verbose and
+/// fragile; instead, we'd much rather write regular C++ code and just parse it;
+/// the APIs defined in this class facilitate this.
+class TokenInjectionHandler {
+protected:
+  TokenInjectionHandler() = default;
+
+public:
+  virtual ~TokenInjectionHandler() = default;
+
+  /// Parse 'Code' as a single expression. Any identifier token whose name is
+  /// equal to a key in 'Replacements' will be replaced with the corresponding
+  /// token in the map before parsing.
+  virtual ExprResult
+  ParseAsExpression(StringRef Code, const llvm::StringMap<Token> &Replacements,
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Sirraide wrote:

Yes, the replacements change on each call because they contain annotation tokens that contain a pointer to a particular expression, which is different for every expansion statement

https://github.com/llvm/llvm-project/pull/208877