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

[Corentin Jabot via cfe-commits]

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@@ -1202,6 +1202,55 @@ StmtResult Parser::ParseCompoundStatementBody(bool isStmtExpr) {
       continue;
     }
 
+    // Annotation token that tells the parser to build the 'begin' and 'end'
+    // declarations for an iterating expansion statement; this is used inside
+    // the lambda that computes the expansion size (see also
+    // Sema::ComputeExpansionSize()).
+    //
+    // The annotation token is followed by 2 identifier tokens, which indicate
+    // the variable names for the begin and end variable, respectively.
+    //
+    // We handle this here because this results in *two* statements, not one,
+    // and moreover, this annotation token shouldn't appear in any other context
+    // anyway.
+    //
+    // The reason this is a single annotation token is that the code that builds
+    // 'begin' and 'end' only supports building both at once.
+    if (Tok.is(tok::annot_expansion_stmt_declare_begin_end)) {
+      auto *RangeVarDecl = static_cast<VarDecl *>(Tok.getAnnotationValue());
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cor3ntin wrote:

why isn't that just reusing `annotation_value_decl` ?

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