Remove msvc preprocessor compat hacks from export_template.h

Bug: 1053958
Change-Id: I07aeae7ebbd5259e030dfad7f1792b44a49b8fc4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2063905Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742624}

base/export_template.h

@@ -40,61 +40,33 @@
 //
 // The implementation of this header uses some subtle macro semantics to
 // detect what the provided FOO_EXPORT value was defined as and then
-// to dispatch to appropriate macro definitions.  Unfortunately,
-// MSVC's C preprocessor is rather non-compliant and requires special
-// care to make it work.
-//
-// Issue 1.
-//
-//   #define F(x)
-//   F()
-//
-// MSVC emits warning C4003 ("not enough actual parameters for macro
-// 'F'), even though it's a valid macro invocation.  This affects the
-// macros below that take just an "export" parameter, because export
-// may be empty.
-//
-// As a workaround, we can add a dummy parameter and arguments:
-//
-//   #define F(x,_)
-//   F(,)
-//
-// Issue 2.
-//
-//   #define F(x) G##x
-//   #define Gj() ok
-//   F(j())
-//
-// The correct replacement for "F(j())" is "ok", but MSVC replaces it
-// with "Gj()".  As a workaround, we can pass the result to an
-// identity macro to force MSVC to look for replacements again.  (This
-// is why EXPORT_TEMPLATE_STYLE_3 exists.)
+// to dispatch to appropriate macro definitions.
 
 #define EXPORT_TEMPLATE_DECLARE(export) \
-  EXPORT_TEMPLATE_INVOKE(DECLARE, EXPORT_TEMPLATE_STYLE(export, ), export)
+  EXPORT_TEMPLATE_INVOKE(DECLARE, EXPORT_TEMPLATE_STYLE(export), export)
 #define EXPORT_TEMPLATE_DEFINE(export) \
-  EXPORT_TEMPLATE_INVOKE(DEFINE, EXPORT_TEMPLATE_STYLE(export, ), export)
+  EXPORT_TEMPLATE_INVOKE(DEFINE, EXPORT_TEMPLATE_STYLE(export), export)
 
 // INVOKE is an internal helper macro to perform parameter replacements
 // and token pasting to chain invoke another macro.  E.g.,
 //     EXPORT_TEMPLATE_INVOKE(DECLARE, DEFAULT, FOO_EXPORT)
 // will export to call
-//     EXPORT_TEMPLATE_DECLARE_DEFAULT(FOO_EXPORT, )
+//     EXPORT_TEMPLATE_DECLARE_DEFAULT(FOO_EXPORT)
 // (but with FOO_EXPORT expanded too).
 #define EXPORT_TEMPLATE_INVOKE(which, style, export) \
   EXPORT_TEMPLATE_INVOKE_2(which, style, export)
 #define EXPORT_TEMPLATE_INVOKE_2(which, style, export) \
-  EXPORT_TEMPLATE_##which##_##style(export, )
+  EXPORT_TEMPLATE_##which##_##style(export)
 
 // Default style is to apply the FOO_EXPORT macro at declaration sites.
-#define EXPORT_TEMPLATE_DECLARE_DEFAULT(export, _) export
-#define EXPORT_TEMPLATE_DEFINE_DEFAULT(export, _)
+#define EXPORT_TEMPLATE_DECLARE_DEFAULT(export) export
+#define EXPORT_TEMPLATE_DEFINE_DEFAULT(export)
 
 // The "MSVC hack" style is used when FOO_EXPORT is defined
 // as __declspec(dllexport), which MSVC requires to be used at
 // definition sites instead.
-#define EXPORT_TEMPLATE_DECLARE_MSVC_HACK(export, _)
-#define EXPORT_TEMPLATE_DEFINE_MSVC_HACK(export, _) export
+#define EXPORT_TEMPLATE_DECLARE_MSVC_HACK(export)
+#define EXPORT_TEMPLATE_DEFINE_MSVC_HACK(export) export
 
 // EXPORT_TEMPLATE_STYLE is an internal helper macro that identifies which
 // export style needs to be used for the provided FOO_EXPORT macro definition.
@@ -105,17 +77,14 @@
 // __declspec annotations into macro invocations.  E.g., if FOO_EXPORT is
 // defined as "__declspec(dllimport)", it undergoes the following sequence of
 // macro substitutions:
-//     EXPORT_TEMPLATE_STYLE(FOO_EXPORT, )
-//     EXPORT_TEMPLATE_STYLE_2(__declspec(dllimport), )
-//     EXPORT_TEMPLATE_STYLE_3(EXPORT_TEMPLATE_STYLE_MATCH__declspec(dllimport))
+//     EXPORT_TEMPLATE_STYLE(FOO_EXPORT)
+//     EXPORT_TEMPLATE_STYLE_2(__declspec(dllimport))
 //     EXPORT_TEMPLATE_STYLE_MATCH__declspec(dllimport)
 //     EXPORT_TEMPLATE_STYLE_MATCH_DECLSPEC_dllimport
 //     DEFAULT
-#define EXPORT_TEMPLATE_STYLE(export, _) EXPORT_TEMPLATE_STYLE_2(export, )
-#define EXPORT_TEMPLATE_STYLE_2(export, _) \
-  EXPORT_TEMPLATE_STYLE_3(                 \
-      EXPORT_TEMPLATE_STYLE_MATCH_foj3FJo5StF0OvIzl7oMxA##export)
-#define EXPORT_TEMPLATE_STYLE_3(style) style
+#define EXPORT_TEMPLATE_STYLE(export) EXPORT_TEMPLATE_STYLE_2(export)
+#define EXPORT_TEMPLATE_STYLE_2(export) \
+  EXPORT_TEMPLATE_STYLE_MATCH_foj3FJo5StF0OvIzl7oMxA##export
 
 // Internal helper macros for EXPORT_TEMPLATE_STYLE.
 //
@@ -144,7 +113,7 @@
 //     EXPORT_TEMPLATE_TEST(DEFAULT, __declspec(dllimport));
 //
 //     static_assert(EXPORT_TEMPLATE_INVOKE(TEST_DEFAULT,
-//         EXPORT_TEMPLATE_STYLE(__declspec(dllimport), ),
+//         EXPORT_TEMPLATE_STYLE(__declspec(dllimport)),
 //         __declspec(dllimport)), "__declspec(dllimport)");
 //
 //     static_assert(EXPORT_TEMPLATE_INVOKE(TEST_DEFAULT,
@@ -157,8 +126,8 @@
 //
 // When they're not working correctly, a syntax error should occur instead.
 #define EXPORT_TEMPLATE_TEST(want, export)                                     \
-  static_assert(EXPORT_TEMPLATE_INVOKE(                                    \
-                    TEST_##want, EXPORT_TEMPLATE_STYLE(export, ), export), \
+  static_assert(EXPORT_TEMPLATE_INVOKE(TEST_##want,                            \
+                                       EXPORT_TEMPLATE_STYLE(export), export), \
                 #export)
 #define EXPORT_TEMPLATE_TEST_DEFAULT_DEFAULT(...) true
 #define EXPORT_TEMPLATE_TEST_MSVC_HACK_MSVC_HACK(...) true