feat: improve robustness of linking with clang path checks (#280)

Author: NathanWalker

project-template-ios/internal/nsld.sh

@@ -58,5 +58,57 @@ GEN_MODULEMAP $TARGET_ARCH
 printf "Generating metadata..."
 GEN_METADATA $TARGET_ARCH
 DELETE_SWIFT_MODULES_DIR
-NS_LD="${NS_LD:-"$TOOLCHAIN_DIR/usr/bin/clang"}"
-$NS_LD "$@"
+
+function resolve_clang() {
+    # 1) If NS_LD is set and executable, honor it.
+    if [[ -n "$NS_LD" && -x "$NS_LD" ]]; then
+        echo "$NS_LD"
+        return 0
+    fi
+
+    # 2) TOOLCHAIN_DIR (if provided)
+    if [[ -n "$TOOLCHAIN_DIR" && -x "$TOOLCHAIN_DIR/usr/bin/clang" ]]; then
+        echo "$TOOLCHAIN_DIR/usr/bin/clang"
+        return 0
+    fi
+
+    # 3) Xcode's DT_TOOLCHAIN_DIR (provided by xcodebuild)
+    if [[ -n "$DT_TOOLCHAIN_DIR" && -x "$DT_TOOLCHAIN_DIR/usr/bin/clang" ]]; then
+        echo "$DT_TOOLCHAIN_DIR/usr/bin/clang"
+        return 0
+    fi
+
+    # 4) xcrun lookup (most reliable within Xcode build env)
+    local xcrun_clang
+    xcrun_clang=$(xcrun --find clang 2>/dev/null) || true
+    if [[ -n "$xcrun_clang" && -x "$xcrun_clang" ]]; then
+        echo "$xcrun_clang"
+        return 0
+    fi
+
+    # 5) Xcode default toolchain from xcode-select
+    local xcode_path
+    xcode_path=$(xcode-select -p 2>/dev/null) || true
+    if [[ -n "$xcode_path" && -x "$xcode_path/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" ]]; then
+        echo "$xcode_path/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang"
+        return 0
+    fi
+
+    # 6) System fallback
+    if [[ -x "/usr/bin/clang" ]]; then
+        echo "/usr/bin/clang"
+        return 0
+    fi
+
+    return 1
+}
+
+CLANG_PATH=$(resolve_clang)
+if [[ -z "$CLANG_PATH" ]]; then
+    echo "NSLD: ERROR: Could not locate a usable clang. TOOLCHAIN_DIR='${TOOLCHAIN_DIR}' DT_TOOLCHAIN_DIR='${DT_TOOLCHAIN_DIR}'."
+    exit 1
+fi
+
+# For visibility downstream, set NS_LD to the resolved path and invoke.
+NS_LD="$CLANG_PATH"
+"$NS_LD" "$@"