[clang] [Clang] Allow raw string literals in C as an extension (PR #88265)

[Aaron Ballman via cfe-commits]

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@@ -130,6 +130,12 @@ struct LangStandard {
   /// hasDigraphs - Language supports digraphs.
   bool hasDigraphs() const { return Flags & Digraphs; }
 
+  /// hasRawStringLiterals - Language supports R"()" raw string literals.
+  bool hasRawStringLiterals() const {
+    // GCC supports raw string literals in C, but not in C++ before C++11.
+    return isCPlusPlus11() || (!isCPlusPlus() && isGNUMode());
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AaronBallman wrote:

GCC doesn't allow them in gnu89 mode: https://godbolt.org/z/hahja6Y87

If I had to hazard a guess as to why, my guess is that there are concerns about `R` conflicting with a user-defined macro. The same concern exists in all versions of C, but code explicitly compiling in C89 mode can be a signal the code isn't being actively maintained in some regard. But still, this is a bit of a surprise, so it might be nice to understand better why the discrepancy exists.

https://github.com/llvm/llvm-project/pull/88265