Add support for LLVM18

Notes:
- Main breakage due to addition of clang::StringLiteralKind enum
  and addition of a new clang module: clangAPINotes.
- There doesn't seem to be a 18.0.0 release at this time
- scripts/build_transpiler.py doesn't build 18.1.1 cleanly
- scripts/test_transpiler.py encountered some failures.
- There is an unresolved linker error from libzstd on macOS.

Closes #1066.

c2rust-ast-exporter/build.rs

@@ -199,6 +199,11 @@ fn build_native(llvm_info: &LLVMInfo) {
             let sema_pos = clang_libs.iter().position(|&r| r == "clangSema").unwrap();
             clang_libs.insert(sema_pos + 1, "clangSupport");
         }
+        if llvm_info.llvm_major_version >= 18 {
+            // insert after clangSupport
+            let sema_pos = clang_libs.iter().position(|&r| r == "clangSupport").unwrap();
+            clang_libs.insert(sema_pos + 1, "clangAPINotes");
+        }
 
         for lib in &clang_libs {
             println!("cargo:rustc-link-lib={}", lib);

c2rust-ast-exporter/src/AstExporter.cpp

@@ -2298,27 +2298,49 @@ class TranslateASTVisitor final
             // C and C++ supports different string types, so
             // we need to identify the string literal type
             switch (SL->getKind()) {
-#if CLANG_VERSION_MAJOR >= 15
+#if CLANG_VERSION_MAJOR >= 18
+            case clang::StringLiteralKind::Ordinary:
+#elif CLANG_VERSION_MAJOR >= 15
             case clang::StringLiteral::StringKind::Ordinary:
 #else
             case clang::StringLiteral::StringKind::Ascii:
 #endif // CLANG_VERSION_MAJOR
                 cbor_encode_uint(array, StringTypeTag::TagAscii);
                 break;
+#if CLANG_VERSION_MAJOR >= 18
+            case clang::StringLiteralKind::Wide:
+#else
             case clang::StringLiteral::StringKind::Wide:
+#endif // CLANG_VERSION_MAJOR
                 cbor_encode_uint(array, StringTypeTag::TagWide);
                 break;
+#if CLANG_VERSION_MAJOR >= 18
+            case clang::StringLiteralKind::UTF8:
+#else
             case clang::StringLiteral::StringKind::UTF8:
+#endif // CLANG_VERSION_MAJOR
                 cbor_encode_uint(array, StringTypeTag::TagUTF8);
                 break;
+#if CLANG_VERSION_MAJOR >= 18
+            case clang::StringLiteralKind::UTF16:
+#else
             case clang::StringLiteral::StringKind::UTF16:
+#endif // CLANG_VERSION_MAJOR
                 cbor_encode_uint(array, StringTypeTag::TagUTF16);
                 break;
+#if CLANG_VERSION_MAJOR >= 18
+            case clang::StringLiteralKind::UTF32:
+#else
             case clang::StringLiteral::StringKind::UTF32:
+#endif // CLANG_VERSION_MAJOR
                 cbor_encode_uint(array, StringTypeTag::TagUTF32);
                 break;
 #if CLANG_VERSION_MAJOR >= 17
+#if CLANG_VERSION_MAJOR >= 18
+            case clang::StringLiteralKind::Unevaluated:
+#else // CLANG_VERSION_MAJOR >= 17
             case clang::StringLiteral::StringKind::Unevaluated:
+#endif
                 cbor_encode_uint(array, StringTypeTag::TagUnevaluated);
                 break;
 #endif // CLANG_VERSION_MAJOR