[llvm] RFC: [llvm] refactor common export macros to llvm/Config (PR #149175)

[Andrew Rogers via llvm-commits]

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@@ -0,0 +1,88 @@
+/*===------- llvm/Config/export-config.h - export configuration ----- C -*-===*/
+/*                                                                            */
+/* Part of the LLVM Project, under the Apache License v2.0 with LLVM          */
+/* Exceptions.                                                                */
+/* See https://llvm.org/LICENSE.txt for license information.                  */
+/* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception                    */
+/*                                                                            */
+/*===----------------------------------------------------------------------===*/
+
+
+/* This file contains configuration definitions controling which LLVM projects
+   and components require public ABI export for shared library builds. It also
+   contains generic LLVM_INTERFACE_ macro definitions that can be aliased by
+   libraries and components and used to decorate their public interface. */
+
+#ifndef LLVM_EXPORT_CONFIG_H
+#define LLVM_EXPORT_CONFIG_H
+
+/* Define if exporting LLVM public interface for shared library */
+#cmakedefine LLVM_ENABLE_LLVM_EXPORT_ANNOTATIONS
+
+/* Define if exporting LLVM-C public interface for shared library */
+#cmakedefine LLVM_ENABLE_LLVM_C_EXPORT_ANNOTATIONS
+
+/// LLVM_INTERFACE_ABI is the main export/visibility macro to mark something as explicitly
+/// exported when llvm is built as a shared library with everything else that is
+/// unannotated will have internal visibility.
+///
+/// LLVM_INTERFACE_ABI_EXPORT is for the special case for things like plugin symbol
+/// declarations or definitions where we don't want the macro to be switching
+/// between dllexport and dllimport on windows based on what codebase is being
+/// built, it will only be dllexport. For non windows platforms this macro
+/// behaves the same as LLVM_ABI.
+///
+/// LLVM_INTERFACE_EXPORT_TEMPLATE is used on explicit template instantiations in source
+/// files that were declared extern in a header. This macro is only set as a
+/// compiler export attribute on windows, on other platforms it does nothing.
+///
+/// LLVM_INTERFACE_TEMPLATE_ABI is for annotating extern template declarations in headers
+/// for both functions and classes. On windows its turned in to dllimport for
+/// library consumers, for other platforms its a default visibility attribute.
+///
+/// LLVM_INTERFACE_ABI_FOR_TEST is for annotating symbols that are only exported because
+/// they are imported from a test. These symbols are not technically part of the
+/// LLVM public interface and could be conditionally excluded when not building
+/// tests in the future.
+///
+// Marker to add to classes or functions in public headers that should not have
+// export macros added to them by the clang tool
+#define LLVM_INTERFACE_ABI_NOT_EXPORTED
+// TODO(https://github.com/llvm/llvm-project/issues/145406): eliminate need for
+// two preprocessor definitions to gate LLVM_ABI macro definitions.
+#if !defined(LLVM_BUILD_STATIC)
+#if defined(_WIN32) && !defined(__MINGW32__)
+#if defined(LLVM_EXPORTS)
----------------
andrurogerz wrote:

> The de-duplication is not worth additional complexity and introducing new patterns IMO.

I am completely on-board with the complexity argument for not doing it this way. I will put up the `abi-breaking` PR again with the duplicated logic.

https://github.com/llvm/llvm-project/pull/149175