Pass sysroot explicitly to libclang on macOS

Author: saraedum

include/cppast/compile_config.hpp

@@ -168,6 +168,13 @@ class compile_config
         return do_use_c();
     }
 
+    /// \effects Appends a raw compiler flag (e.g. `-isysroot <path>`).
+    /// Use this to forward driver-level options that have no dedicated setter.
+    void add_flag(std::string flag)
+    {
+        flags_.push_back(std::move(flag));
+    }
+
 protected:
     compile_config(std::vector<std::string> def_flags) : flags_(std::move(def_flags)) {}
 
@@ -176,11 +183,6 @@ class compile_config
 
     ~compile_config() noexcept = default;
 
-    void add_flag(std::string flag)
-    {
-        flags_.push_back(std::move(flag));
-    }
-
     const std::vector<std::string>& get_flags() const noexcept
     {
         return flags_;

test/integration.cpp

@@ -5,8 +5,27 @@
 
 #include <cppast/cpp_preprocessor.hpp>
 
+#include <cstdlib>
+
 using namespace cppast;
 
+#ifdef __APPLE__
+namespace
+{
+// libclang's embedded driver doesn't auto-detect the Apple SDK from SDKROOT
+// for clang_parseTranslationUnit (only the driver binary does). Forward
+// -isysroot explicitly so libc++ headers can find <stdlib.h>, <wchar.h>, etc.
+void apply_macos_sysroot(libclang_compile_config& config)
+{
+    if (auto sdkroot = std::getenv("SDKROOT"))
+    {
+        config.add_flag("-isysroot");
+        config.add_flag(sdkroot);
+    }
+}
+} // namespace
+#endif
+
 TEST_CASE("stdlib", "[.][integration]")
 {
     auto code = R"(
@@ -105,6 +124,9 @@ TEST_CASE("stdlib", "[.][integration]")
 
     libclang_compile_config config;
     config.set_flags(cpp_standard::cpp_latest);
+#ifdef __APPLE__
+    apply_macos_sysroot(config);
+#endif
     auto file = parser.parse("stdlib.cpp", config);
     REQUIRE(!parser.error());
     REQUIRE(file);
@@ -126,6 +148,9 @@ TEST_CASE("cppast", "[integration]")
     libclang_compile_config       config(database, CPPAST_INTEGRATION_FILE);
     config.set_flags(cpp_standard::cpp_latest);
     config.fast_preprocessing(true);
+#ifdef __APPLE__
+    apply_macos_sysroot(config);
+#endif
     parse_files(parser, files, config);
 
     REQUIRE(!parser.error());