Allow linking with -lSDL2_mixer to work properly

ChangeLog.md

@@ -23,6 +23,9 @@ Current Trunk
 - dlopen, in conformace with the spec, now checks that one of either RTDL_LAZY
   or RTDL_NOW flags ar set.  Previously, it was possible set nether of these
   without generating an error.
+- Allow `-lSDL2_mixer` to just work. (Others like `-lSDL2` always worked, but
+  for `SDL2_mixer` things were broken because we build multiple variations of
+  that library.) That link flag is now the same as `-s USE_SDL2_MIXER=2`.
 - Stack state is no longer stored in JavaScript.  The following variables have
   been replaced with native functions in `<emscripten/stack.h>`:
   - STACK_BASE

emcc.py

@@ -3167,6 +3167,8 @@ def process_libraries(libs, lib_dirs, temp_files):
       if jslibs is not None:
         libraries += [(i, jslib) for jslib in jslibs]
         consumed.append(i)
+      elif building.map_and_apply_to_settings(lib):
+        consumed.append(i)
 
   shared.Settings.SYSTEM_JS_LIBRARIES += libraries
 

tests/sdl2_mixer_wav.c

@@ -1,3 +1,4 @@
+#include <assert.h>
 #include <emscripten.h>
 #include <SDL2/SDL.h>
 #include <SDL2/SDL_mixer.h>
@@ -21,8 +22,18 @@ void sound_loop_then_quit() {
 }
 
 int main(int argc, char* argv[]){
-    if (SDL_Init(SDL_INIT_AUDIO) < 0)
-        return -1;
+    SDL_version version;
+    SDL_GetVersion(&version);
+    printf("Linked against SDL %d.%d.%d.\n",
+           version.major, version.minor, version.patch);
+    assert(version.major == 2);
+
+    if (SDL_Init(SDL_INIT_AUDIO) < 0) {
+        puts("Failed to init audio");
+#ifdef REPORT_RESULT
+        REPORT_RESULT(100);
+#endif
+    }
     int const frequency = EM_ASM_INT_V({
         var context;
         try {
@@ -32,13 +43,25 @@ int main(int argc, char* argv[]){
         }
         return context.sampleRate;
     });
-    if(Mix_OpenAudio(frequency, MIX_DEFAULT_FORMAT, 2, 1024) == -1)
-        return -1;
+    if(Mix_OpenAudio(frequency, MIX_DEFAULT_FORMAT, 2, 1024) == -1) {
+        puts("Failed to open audio");
+#ifdef REPORT_RESULT
+        REPORT_RESULT(101);
+#endif
+    }
     wave = Mix_LoadWAV(WAV_PATH);
-    if (wave == NULL)
-        return -1;
-    if (Mix_PlayChannel(-1, wave, 0) == -1)
-        return -1;
+    if (wave == NULL) {
+        puts("Failed to load audio");
+#ifdef REPORT_RESULT
+        REPORT_RESULT(102);
+#endif
+    }
+    if (Mix_PlayChannel(-1, wave, 0) == -1) {
+        puts("Failed to play audio");
+#ifdef REPORT_RESULT
+        REPORT_RESULT(103);
+#endif
+    }
     printf("Starting sound play loop\n");
     emscripten_set_main_loop(sound_loop_then_quit, 0, 1);
     return 0;

tests/test_browser.py

@@ -3121,10 +3121,14 @@ def test_sdl2_misc(self):
     self.compile_btest(['test.o', '-s', 'USE_SDL=2', '-o', 'test.html'])
     self.run_browser('test.html', '...', '/report_result?1')
 
+  @parameterized({
+    'dash_s': (['-s', 'USE_SDL=2', '-s', 'USE_SDL_MIXER=2'],),
+    'dash_l': (['-lSDL2', '-lSDL2_mixer'],),
+  })
   @requires_sound_hardware
-  def test_sdl2_mixer_wav(self):
+  def test_sdl2_mixer_wav(self, flags):
     shutil.copyfile(path_from_root('tests', 'sounds', 'the_entertainer.wav'), 'sound.wav')
-    self.btest('sdl2_mixer_wav.c', expected='1', args=['--preload-file', 'sound.wav', '-s', 'USE_SDL=2', '-s', 'USE_SDL_MIXER=2', '-s', 'INITIAL_MEMORY=33554432'])
+    self.btest('sdl2_mixer_wav.c', expected='1', args=['--preload-file', 'sound.wav', '-s', 'INITIAL_MEMORY=33554432'] + flags)
 
   @parameterized({
     'wav': ([],         '0',            'the_entertainer.wav'),

tools/building.py

@@ -1465,6 +1465,26 @@ def map_to_js_libs(library_name):
   return None
 
 
+# map a linker flag to a Settings option, and apply it. this lets a user write
+# -lSDL2 and it will have the same effect as -s USE_SDL=2.
+def map_and_apply_to_settings(library_name):
+  # most libraries just work, because the -l name matches the name of the
+  # library we build. however, if a library has variations, which cause us to
+  # build multiple versions with multiple names, then we need this mechanism.
+  library_map = {
+    # SDL2_mixer's built library name contains the specific codecs built in.
+    'SDL2_mixer': [('USE_SDL_MIXER', 2)],
+  }
+
+  if library_name in library_map:
+    for key, value in library_map[library_name]:
+      logger.debug('Mapping library `%s` to settings changes: %s = %s' % (library_name, key, value))
+      setattr(shared.Settings, key, value)
+    return True
+
+  return False
+
+
 def emit_wasm_source_map(wasm_file, map_file):
   # source file paths must be relative to the location of the map (which is
   # emitted alongside the wasm)