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diff --git a/libbuild2/cxx/export.hxx b/libbuild2/cxx/export.hxx
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+// file      : libbuild2/cxx/export.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#pragma once
+
+// Normally we don't export class templates (but do complete specializations),
+// inline functions, and classes with only inline member functions. Exporting
+// classes that inherit from non-exported/imported bases (e.g., std::string)
+// will end up badly. The only known workarounds are to not inherit or to not
+// export. Also, MinGW GCC doesn't like seeing non-exported functions being
+// used before their inline definition. The workaround is to reorder code. In
+// the end it's all trial and error.
+
+#if defined(LIBBUILD2_CXX_STATIC)         // Using static.
+#  define LIBBUILD2_CXX_SYMEXPORT
+#elif defined(LIBBUILD2_CXX_STATIC_BUILD) // Building static.
+#  define LIBBUILD2_CXX_SYMEXPORT
+#elif defined(LIBBUILD2_CXX_SHARED)       // Using shared.
+#  ifdef _WIN32
+#    define LIBBUILD2_CXX_SYMEXPORT __declspec(dllimport)
+#  else
+#    define LIBBUILD2_CXX_SYMEXPORT
+#  endif
+#elif defined(LIBBUILD2_CXX_SHARED_BUILD) // Building shared.
+#  ifdef _WIN32
+#    define LIBBUILD2_CXX_SYMEXPORT __declspec(dllexport)
+#  else
+#    define LIBBUILD2_CXX_SYMEXPORT
+#  endif
+#else
+// If none of the above macros are defined, then we assume we are being used
+// by some third-party build system that cannot/doesn't signal the library
+// type. Note that this fallback works for both static and shared but in case
+// of shared will be sub-optimal compared to having dllimport.
+//
+#  define LIBBUILD2_CXX_SYMEXPORT         // Using static or shared.
+#endif