Turn libfmt-c into a shared library (#4812)

Linux distros don't like having static archives. Set fmt-c to shared
just like the main fmt library.

Author: jengelh

CMakeLists.txt

@@ -417,8 +417,19 @@ target_compile_definitions(fmt-header-only INTERFACE FMT_HEADER_ONLY=1)
 target_compile_features(fmt-header-only INTERFACE cxx_std_11)
 setup_target(fmt-header-only INTERFACE)
 
-add_library(fmt-c STATIC src/fmt-c.cc)
+add_library(fmt-c src/fmt-c.cc)
 target_compile_features(fmt-c INTERFACE c_std_11)
+if (BUILD_SHARED_LIBS)
+  target_compile_definitions(
+    fmt-c
+    PRIVATE FMT_LIB_EXPORT
+    INTERFACE FMT_SHARED)
+endif ()
+set_target_properties(
+  fmt-c
+  PROPERTIES VERSION ${FMT_VERSION}
+             SOVERSION ${CPACK_PACKAGE_VERSION_MAJOR}
+             DEBUG_POSTFIX "${FMT_DEBUG_POSTFIX}")
 if (MSVC)
   target_compile_options(fmt-c PUBLIC /Zc:preprocessor)
 endif ()

include/fmt/fmt-c.h

@@ -12,6 +12,25 @@
 #include <stddef.h>   // size_t
 #include <stdio.h>    // FILE
 
+#if defined(__GNUC__)
+#  define FMT_CVISIBILITY(value) __attribute__((visibility(value)))
+#else
+#  define FMT_CVISIBILITY(value)
+#endif
+
+#if !defined(FMT_HEADER_ONLY) && defined(_WIN32)
+#  if defined(FMT_LIB_EXPORT)
+#    define FMT_CAPI __declspec(dllexport)
+#  elif defined(FMT_SHARED)
+#    define FMT_CAPI __declspec(dllimport)
+#  endif
+#elif defined(FMT_LIB_EXPORT) || defined(FMT_SHARED)
+#  define FMT_CAPI FMT_CVISIBILITY("default")
+#endif
+#ifndef FMT_CAPI
+#  define FMT_CAPI
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -45,10 +64,10 @@ typedef struct {
 
 enum { fmt_error = -1, fmt_error_invalid_arg = -2 };
 
-int fmt_vformat(char* buffer, size_t size, const char* fmt, const fmt_arg* args,
-                size_t num_args);
-int fmt_vprint(FILE* stream, const char* fmt, const fmt_arg* args,
-               size_t num_args);
+int FMT_CAPI fmt_vformat(char* buffer, size_t size, const char* fmt,
+                         const fmt_arg* args, size_t num_args);
+int FMT_CAPI fmt_vprint(FILE* stream, const char* fmt, const fmt_arg* args,
+                        size_t num_args);
 
 #ifdef __cplusplus
 }
@@ -92,7 +111,7 @@ static inline fmt_arg fmt_from_ptr(const void* x) {
   return (fmt_arg){.type = fmt_pointer, .value.pointer = x};
 }
 
-void fmt_unsupported_type(void);
+void FMT_CAPI fmt_unsupported_type(void);
 
 #  if !defined(_MSC_VER) || defined(__clang__)
 typedef signed char fmt_signed_char;

test/CMakeLists.txt

@@ -243,5 +243,5 @@ endif ()
 
 enable_language(C)
 add_executable(c-test c-test.c)
-target_link_libraries(c-test PRIVATE fmt::fmt-c)
+target_link_libraries(c-test PUBLIC fmt::fmt-c)
 add_test(NAME c-test COMMAND c-test)