Build DLLs on Cygwin and MinGW.

CHANGES.txt

@@ -30,6 +30,8 @@
     UTF-8 bytes.
   * Compiled-in message types can now contain dynamic extensions, through use
     of CodedInputStream::SetExtensionRegistry().
+  * Now compiles shared libraries (DLLs) by default on Cygwin and MinGW, to
+    match other platforms.  Use --disable-shared to avoid this.
 
   Java
   * parseDelimitedFrom() and mergeDelimitedFrom() now detect EOF and return

src/Makefile.am

@@ -76,7 +76,7 @@ nobase_include_HEADERS =                                       \
 lib_LTLIBRARIES = libprotobuf-lite.la libprotobuf.la libprotoc.la
 
 libprotobuf_lite_la_LIBADD = $(PTHREAD_LIBS)
-libprotobuf_lite_la_LDFLAGS = -version-info 6:0:0
+libprotobuf_lite_la_LDFLAGS = -version-info 6:0:0 -export-dynamic -no-undefined
 libprotobuf_lite_la_SOURCES =                                  \
   google/protobuf/stubs/common.cc                              \
   google/protobuf/stubs/once.cc                                \
@@ -95,7 +95,7 @@ libprotobuf_lite_la_SOURCES =                                  \
   google/protobuf/io/zero_copy_stream_impl_lite.cc
 
 libprotobuf_la_LIBADD = $(PTHREAD_LIBS)
-libprotobuf_la_LDFLAGS = -version-info 6:0:0
+libprotobuf_la_LDFLAGS = -version-info 6:0:0 -export-dynamic -no-undefined
 libprotobuf_la_SOURCES =                                       \
   $(libprotobuf_lite_la_SOURCES)                               \
   google/protobuf/stubs/strutil.cc                             \
@@ -123,7 +123,7 @@ libprotobuf_la_SOURCES =                                       \
   google/protobuf/compiler/parser.cc
 
 libprotoc_la_LIBADD = $(PTHREAD_LIBS) libprotobuf.la
-libprotoc_la_LDFLAGS = -version-info 6:0:0
+libprotoc_la_LDFLAGS = -version-info 6:0:0 -export-dynamic -no-undefined
 libprotoc_la_SOURCES =                                         \
   google/protobuf/compiler/code_generator.cc                   \
   google/protobuf/compiler/command_line_interface.cc           \

src/google/protobuf/compiler/command_line_interface_unittest.cc

@@ -68,6 +68,9 @@ namespace compiler {
 #ifndef STDOUT_FILENO
 #define STDOUT_FILENO 1
 #endif
+#ifndef F_OK
+#define F_OK 00  // not defined by MSVC for whatever reason
+#endif
 #endif
 
 namespace {
@@ -248,11 +251,40 @@ void CommandLineInterfaceTest::Run(const string& command) {
 
   if (!disallow_plugins_) {
     cli_.AllowPlugins("prefix-");
-#ifdef _WIN32
-    args.push_back("--plugin=prefix-gen-plug=test_plugin.exe");
-#else
-    args.push_back("--plugin=prefix-gen-plug=test_plugin");
-#endif
+
+    const char* possible_paths[] = {
+      // When building with shared libraries, libtool hides the real executable
+      // in .libs and puts a fake wrapper in the current directory.
+      // Unfortunately, due to an apparent bug on Cygwin/MinGW, if one program
+      // wrapped in this way (e.g. protobuf-tests.exe) tries to execute another
+      // program wrapped in this way (e.g. test_plugin.exe), the latter fails
+      // with error code 127 and no explanation message.  Presumably the problem
+      // is that the wrapper for protobuf-tests.exe set some environment
+      // variables that confuse the wrapper for test_plugin.exe.  Luckily, it
+      // turns out that if we simply invoke the wrapped test_plugin.exe
+      // directly, it works -- I guess the environment variables set by the
+      // protobuf-tests.exe wrapper happen to be correct for it too.  So we do
+      // that.
+      ".libs/test_plugin.exe",  // Win32 w/autotool (Cygwin / MinGW)
+      "test_plugin.exe",        // Other Win32 (MSVC)
+      "test_plugin",            // Unix
+    };
+
+    string plugin_path;
+
+    for (int i = 0; i < GOOGLE_ARRAYSIZE(possible_paths); i++) {
+      if (access(possible_paths[i], F_OK) == 0) {
+        plugin_path = possible_paths[i];
+        break;
+      }
+    }
+
+    if (plugin_path.empty()) {
+      GOOGLE_LOG(ERROR)
+          << "Plugin executable not found.  Plugin tests are likely to fail.";
+    } else {
+      args.push_back("--plugin=prefix-gen-plug=" + plugin_path);
+    }
   }
 
   scoped_array<const char*> argv(new const char*[args.size()]);