common: unify diverged storage-class attributes in globals.h

The immediate reason for this commit is to fix a bug when using the
autools build system with Cygwin, described below, but it is also a
step towards
https://gitlab.com/graphviz/graphviz/-/issues/2058#note_678679545.

This file had one set of Windows-specific storage-class attribute
declarations intended for use with the autotools build system and one
set intended for use with Visual Studio, with slightly different
control mechanisms.

It's unclear what effect changes made to these control mechanisms over
the years has had on the many operating systems that are not tested in
CI. The current state is that they partly overlap and are very hard to
understand.

This commit cleans this up by applying such declarations only if the
GVDLL or the WIN32_DLL symbol is set. An export declaration is used if
either the GVC_EXPORT or the _BLD_GVC symbol is defined and an import
declaration otherwise.

Using both GVDLL and WIN32_DLL for the same purpose is a temporary
measure and will be replaced by only one symbol in an upcoming commit
series towards
https://gitlab.com/graphviz/graphviz/-/issues/2058#note_678679545.

Since https://gitlab.com/graphviz/graphviz/-/merge_requests/2182,
setting GVDLL is the preferred single mechanism to enable those
attributes, rather than using _WIN32 and __CYGWIN__ plus some other
symbol to distinguish between static and dynamic-link/shared
libraries.

Likewise is the use of both GVC_EXPORT and _BLD_gvc for the same
purpose a temporary measure, which will be replaced by only one symbol
in an upcoming commit series towards
https://gitlab.com/graphviz/graphviz/-/issues/2058#note_678679545.

This fixes a segmentation fault when running 'dot -c' during 'make install' on Cygwin.

Debugging with gdb showed that this happened on line 99 in dot.c:
    GvExitOnUsage = 1;

diff --git a/lib/common/globals.h b/lib/common/globals.h
index 30165dab69cd42d96bb5a8c9890008cd0c79b3f7..1c11a2d7ba8d5ff22b252257aa0d1c7693eff5a4 100644 (file)
--- a/lib/common/globals.h
+++ b/lib/common/globals.h
@@ -14,20 +14,13 @@
 extern "C" {
 #endif
 
-#ifndef __CYGWIN__
-#if defined(GVDLL)
-#if !defined(_BLD_gvc)
-#define DECLSPEC       __declspec(dllimport)
-#endif
-#endif
-#endif
-/*visual studio*/
-#ifdef _WIN32
-#ifndef GVC_EXPORTS
+#if defined(GVDLL) || defined(WIN32_DLL)
+#if defined(GVC_EXPORTS) || defined(_BLD_gvc)
+#define DECLSPEC __declspec(dllexport)
+#else
 #define DECLSPEC __declspec(dllimport)
 #endif
 #endif
-/*end visual studio*/
 
 #ifndef DECLSPEC
 #define DECLSPEC /* nothing */