[clang] [llvm] [Clang-Repl] Introduce Error Recovery for Clang-Repl. (PR #223305)

[Vassil Vassilev via cfe-commits]

================
@@ -54,6 +54,7 @@
 namespace clang {
 
 class ASTContext;
+class DeclStateReverter;
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vgvassilev wrote:

Well, the visiting declarations is exactly what this patch is doing in a hand-written way. Consider the existing changes such as:
```diff
+#define PTU_SHAPES                                                             \
+  PTU_SHAPE(Class, CXXRecordDecl)                                              \
+  PTU_SHAPE(Function, FunctionDecl)                                            \
+  PTU_SHAPE(Var, VarDecl)                                                      \
+  PTU_SHAPE(Enum, EnumDecl)                                                    \
+  PTU_SHAPE(Template, RedeclarableTemplateDecl)                                \
+  PTU_SHAPE(Typedef, TypedefNameDecl)
```
They are exactly the dispatching the visitors are ding. Later the checks depending on the declaration kinds are also the same split that you get from a visitor. Help me see the benefits of the current approach wrt the one in the DeclUnmerger?

https://github.com/llvm/llvm-project/pull/223305