feat: Set MACOSX_DEPLOYMENT_TARGET

configure

@@ -50,6 +50,53 @@ else
   echo "*** Detected DEBUG=true, do not override CARGO_HOME"
 fi
 
+# Detect macOS deployment target for Rust cc crate.
+# Although we export CC and CFLAGS to cargo, the cc crate does not derive the
+# deployment target from these flags. Instead, it has its own lookup:
+# MACOSX_DEPLOYMENT_TARGET env var first, then `xcrun --show-sdk-version` as
+# fallback. It passes the result as -mmacosx-version-min=<value> to the compiler.
+# Without MACOSX_DEPLOYMENT_TARGET, the fallback SDK version (e.g. 26.2) can
+# exceed the target R's compiler uses, causing an ld warning about version mismatch.
+#
+# Credits:
+#   - clarabel-r: https://github.com/oxfordcontrol/clarabel-r/commit/a3d5ec6a
+#   - tinyimg: https://github.com/yihui/tinyimg/pull/20
+if [ "$(uname)" = "Darwin" ]; then
+  if [ -z "$MACOSX_DEPLOYMENT_TARGET" ]; then
+    R_CC=$("${R_HOME}/bin/R" CMD config CC)
+    R_CFLAGS=$("${R_HOME}/bin/R" CMD config CFLAGS)
+
+    # First, check if R's CC or CFLAGS contain -mmacosx-version-min=.
+    # This is the most direct way to detect the deployment target R was
+    # configured with.
+    R_FLAGS="${R_CC} ${R_CFLAGS}"
+    MACOSX_DEPLOYMENT_TARGET=$(echo "${R_FLAGS}" | \
+      sed -n 's/.*-mmacosx-version-min=\([0-9][0-9.]*\).*/\1/p' | head -n 1)
+
+    if [ -z "${MACOSX_DEPLOYMENT_TARGET}" ]; then
+      # Fallback: __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ is a
+      # preprocessor macro that Apple clang defines to indicate the minimum
+      # macOS version the compiled code will target. It is an integer encoding
+      # of the version: major * 10000 + minor * 100 + patch (e.g. 150000 =
+      # macOS 15.0.0). We preprocess an empty file with R's CC to read this
+      # value, then convert it back to a "major.minor" version string.
+      MACOSX_VERSION_MIN=$(echo "" | ${R_CC} ${R_CFLAGS} -dM -E - 2>/dev/null | \
+        grep '__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__' | \
+        awk '{print $3}')
+      if [ -n "${MACOSX_VERSION_MIN}" ]; then
+        MAJOR=$(expr "${MACOSX_VERSION_MIN}" / 10000)
+        MINOR=$(expr "${MACOSX_VERSION_MIN}" / 100 % 100)
+        MACOSX_DEPLOYMENT_TARGET="${MAJOR}.${MINOR}"
+      fi
+    fi
+  fi
+
+  if [ -n "${MACOSX_DEPLOYMENT_TARGET}" ]; then
+    echo "using macOS deployment target: ${MACOSX_DEPLOYMENT_TARGET}"
+    BEFORE_CARGO_BUILD="${BEFORE_CARGO_BUILD}"' export MACOSX_DEPLOYMENT_TARGET="'"${MACOSX_DEPLOYMENT_TARGET}"'" \&\&'
+  fi
+fi
+
 sed \
   -e "s|@BEFORE_CARGO_BUILD@|${BEFORE_CARGO_BUILD}|" \
   -e "s|@VENDORING@|${VENDORING}|" \