1 // Copyright 2018 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_COMPONENT_EXPORT_H_ 6 #define BASE_COMPONENT_EXPORT_H_ 7 8 #include "build/build_config.h" 9 10 // Used to annotate symbols which are exported by the component named 11 // |component|. Note that this only does the right thing if the corresponding 12 // component target's sources are compiled with |IS_$component_IMPL| defined 13 // as 1. For example: 14 // 15 // class COMPONENT_EXPORT(FOO) Bar {}; 16 // 17 // If IS_FOO_IMPL=1 at compile time, then Bar will be annotated using the 18 // COMPONENT_EXPORT_ANNOTATION macro defined below. Otherwise it will be 19 // annotated using the COMPONENT_IMPORT_ANNOTATION macro. 20 #define COMPONENT_EXPORT(component) \ 21 COMPONENT_MACRO_CONDITIONAL_(IS_##component##_IMPL, \ 22 COMPONENT_EXPORT_ANNOTATION, \ 23 COMPONENT_IMPORT_ANNOTATION) 24 25 // Indicates whether the current compilation unit is being compiled as part of 26 // the implementation of the component named |component|. Expands to |1| if 27 // |IS_$component_IMPL| is defined as |1|; expands to |0| otherwise. 28 // 29 // Note in particular that if |IS_$component_IMPL| is not defined at all, it is 30 // still fine to test INSIDE_COMPONENT_IMPL(component), which expands to |0| as 31 // expected. 32 #define INSIDE_COMPONENT_IMPL(component) \ 33 COMPONENT_MACRO_CONDITIONAL_(IS_##component##_IMPL, 1, 0) 34 35 // Compiler-specific macros to annotate for export or import of a symbol. No-op 36 // in non-component builds. These should not see much if any direct use. 37 // Instead use the COMPONENT_EXPORT macro defined above. 38 #if defined(COMPONENT_BUILD) 39 #if defined(WIN32) 40 #define COMPONENT_EXPORT_ANNOTATION __declspec(dllexport) 41 #define COMPONENT_IMPORT_ANNOTATION __declspec(dllimport) 42 #else // defined(WIN32) 43 #define COMPONENT_EXPORT_ANNOTATION __attribute__((visibility("default"))) 44 #define COMPONENT_IMPORT_ANNOTATION 45 #endif // defined(WIN32) 46 #else // defined(COMPONENT_BUILD) 47 #define COMPONENT_EXPORT_ANNOTATION 48 #define COMPONENT_IMPORT_ANNOTATION 49 #endif // defined(COMPONENT_BUILD) 50 51 // Below this point are several internal utility macros used for the 52 // implementation of the above macros. Not intended for external use. 53 54 // Helper for conditional expansion to one of two token strings. If |condition| 55 // expands to |1| then this macro expands to |consequent|; otherwise it expands 56 // to |alternate|. 57 #define COMPONENT_MACRO_CONDITIONAL_(condition, consequent, alternate) \ 58 COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_( \ 59 COMPONENT_MACRO_CONDITIONAL_COMMA_(condition), consequent, alternate) 60 61 // Expands to a comma (,) iff its first argument expands to |1|. Used in 62 // conjunction with |COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_()|, as the presence 63 // or absense of an extra comma can be used to conditionally shift subsequent 64 // argument positions and thus influence which argument is selected. 65 #define COMPONENT_MACRO_CONDITIONAL_COMMA_(...) \ 66 COMPONENT_MACRO_CONDITIONAL_COMMA_IMPL_(__VA_ARGS__,) 67 #define COMPONENT_MACRO_CONDITIONAL_COMMA_IMPL_(x, ...) \ 68 COMPONENT_MACRO_CONDITIONAL_COMMA_##x##_ 69 #define COMPONENT_MACRO_CONDITIONAL_COMMA_1_ , 70 71 // Helper which simply selects its third argument. Used in conjunction with 72 // |COMPONENT_MACRO_CONDITIONAL_COMMA_()| above to implement conditional macro 73 // expansion. 74 #define COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_(...) \ 75 COMPONENT_MACRO_EXPAND_( \ 76 COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_IMPL_(__VA_ARGS__)) 77 #define COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_IMPL_(a, b, c, ...) c 78 79 // Helper to work around MSVC quirkiness wherein a macro expansion like |,| 80 // within a parameter list will be treated as a single macro argument. This is 81 // needed to ensure that |COMPONENT_MACRO_CONDITIONAL_COMMA_()| above can expand 82 // to multiple separate positional arguments in the affirmative case, thus 83 // elliciting the desired conditional behavior with 84 // |COMPONENT_MACRO_SELECT_THIRD_ARGUMENT_()|. 85 #define COMPONENT_MACRO_EXPAND_(x) x 86 87 #endif // BASE_COMPONENT_EXPORT_H_ 88