[clang] [C2y] Add octal prefixes, deprecate unprefixed octals (PR #131626)

[via cfe-commits]

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@@ -256,6 +256,14 @@ def warn_cxx17_hex_literal : Warning<
   "hexadecimal floating literals are incompatible with "
   "C++ standards before C++17">,
   InGroup<CXXPre17CompatPedantic>, DefaultIgnore;
+def ext_octal_literal : Extension<
+  "octal integer literals are a C2y extension">, InGroup<C2y>;
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cor3ntin wrote:

I would rather we say it's a clang extension in C++ mode

https://github.com/llvm/llvm-project/pull/131626