fix windows export

Author: wgtmac

src/iceberg/iceberg_export.h

@@ -27,8 +27,31 @@
 #  else
 #    define ICEBERG_EXPORT __declspec(dllimport)
 #  endif
-#else  // Not Windows
+
+#  define ICEBERG_TEMPLATE_EXPORT ICEBERG_EXPORT
+
+// Visibility for template class declarations.
+// Keep empty on MSVC to avoid `extern` + `dllexport` C4910 interactions.
+#  if defined(_MSC_VER)
+#    define ICEBERG_TEMPLATE_TYPE_EXPORT
+#  else
+#    define ICEBERG_TEMPLATE_TYPE_EXPORT ICEBERG_EXPORT
+#  endif
+
+// MSVC doesn't allow explicit instantiation declarations as `extern` +
+// `__declspec(dllexport)` (C4910).
+#  if defined(_MSC_VER) && defined(ICEBERG_EXPORTING) && !defined(ICEBERG_STATIC)
+#    define ICEBERG_EXTERN_TEMPLATE_EXPORT
+#  else
+#    define ICEBERG_EXTERN_TEMPLATE_EXPORT ICEBERG_TEMPLATE_EXPORT
+#  endif
+
+#else  // Non-Windows
 #  ifndef ICEBERG_EXPORT
 #    define ICEBERG_EXPORT __attribute__((visibility("default")))
 #  endif
+
+#  define ICEBERG_TEMPLATE_EXPORT
+#  define ICEBERG_TEMPLATE_TYPE_EXPORT ICEBERG_EXPORT
+#  define ICEBERG_EXTERN_TEMPLATE_EXPORT ICEBERG_TEMPLATE_EXPORT
 #endif

src/iceberg/util/struct_like_set.cc

@@ -617,7 +617,7 @@ bool StructLikeSet<kValidate>::KeyEqual::operator()(
   return StructLikeEqualUnchecked(*lhs, rhs);
 }
 
-template class StructLikeSet<true>;
-template class StructLikeSet<false>;
+template class ICEBERG_TEMPLATE_EXPORT StructLikeSet<true>;
+template class ICEBERG_TEMPLATE_EXPORT StructLikeSet<false>;
 
 }  // namespace iceberg

src/iceberg/util/struct_like_set.h

@@ -45,7 +45,7 @@ namespace iceberg {
 /// only when the caller guarantees schema conformance and the validation
 /// overhead must be avoided.
 template <bool kValidate = true>
-class ICEBERG_EXPORT StructLikeSet {
+class ICEBERG_TEMPLATE_TYPE_EXPORT StructLikeSet {
  public:
   /// \brief Create a StructLikeSet for the given struct type.
   explicit StructLikeSet(const StructType& type);
@@ -102,7 +102,7 @@ class ICEBERG_EXPORT StructLikeSet {
 /// that guarantee schema conformance.
 using UncheckedStructLikeSet = StructLikeSet<false>;
 
-extern template class StructLikeSet<true>;
-extern template class StructLikeSet<false>;
+extern template class ICEBERG_EXTERN_TEMPLATE_EXPORT StructLikeSet<true>;
+extern template class ICEBERG_EXTERN_TEMPLATE_EXPORT StructLikeSet<false>;
 
 }  // namespace iceberg