Allow linking with -lSDL2_mixer to work properly (#12633)

This did not just work because we build libSDL2_mixer_ogg etc., with a suffix
for the codecs we build in. This PR adds an explicit mapping to handle such
cases.

Also improve the test to check this, and add a lot more checks there, like that
we don't use SDL1 somehow (which can happen with files like this where the
SDL1 and SDL2 APIs agree, and so SDL2 does not need to be linked in to
get a running executable).

Fixes #12589

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

@@ -3157,6 +3157,8 @@ 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)