[clang] [clang-repl] adding documentation and information for %commands (PR #150348)

[David Spickett via cfe-commits]

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@@ -370,6 +379,10 @@ int main(int argc, const char **argv) {
       if (Input == R"(%undo)") {
         if (auto Err = Interp->Undo())
           llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
+      } else if (Input == R"(%help)") {
+        OS << help_output << '\n';
+      } else if (Input[0] == '%') { // make sure this is evaluated last
+        OS << "Invalid % command: \"" << Input << "\". " << help_prompt;
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DavidSpickett wrote:

For this I think you should handle it as if it were an error that came from an attempt to undo. Except in this case, you'd construct an error yourself and pass that into logAllUnhandledErrors.

https://github.com/llvm/llvm-project/pull/150348