Add EXPORT_KEEPALIVE to export symbols even in MINIMAL_RUNTIME

Author: DavidPeicho

emcc.py

@@ -1959,6 +1959,8 @@ def phase_linker_setup(options, state, newargs):
     default_setting('SUPPORT_ERRNO', 0)
     # Require explicit -lfoo.js flags to link with JS libraries.
     default_setting('AUTO_JS_LIBRARIES', 0)
+    # When using MINIMAL_RUNTIME, symbols should only be exported if requested.
+    default_setting('EXPORT_KEEPALIVE', 0)
 
   if settings.STRICT_JS and (settings.MODULARIZE or settings.EXPORT_ES6):
     exit_with_error("STRICT_JS doesn't work with MODULARIZE or EXPORT_ES6")

emscripten.py

@@ -740,7 +740,7 @@ def install_wrapper(sym):
     wrapper = '/** @type {function(...*):?} */\nvar %s = ' % mangled
 
     # TODO(sbc): Can we avoid exporting the dynCall_ functions on the module.
-    if mangled in settings.EXPORTED_FUNCTIONS or name.startswith('dynCall_'):
+    if name.startswith('dynCall_') or (settings.EXPORT_KEEPALIVE and mangled in settings.EXPORTED_FUNCTIONS):
       exported = 'Module["%s"] = ' % mangled
     else:
       exported = ''
@@ -793,8 +793,9 @@ def create_receiving(exports):
         mangled = asmjs_mangle(s)
         dynCallAssignment = ('dynCalls["' + s.replace('dynCall_', '') + '"] = ') if generate_dyncall_assignment and mangled.startswith('dynCall_') else ''
         export_assignment = ''
-        if settings.MODULARIZE and settings.EXPORT_ALL:
-          export_assignment = f'Module["{mangled}"] = '
+        if settings.MODULARIZE:
+          if settings.EXPORT_ALL or (settings.EXPORT_KEEPALIVE and mangled in settings.EXPORTED_FUNCTIONS):
+            export_assignment = f'Module["{mangled}"] = '
         receiving += [f'{export_assignment}{dynCallAssignment}{mangled} = asm["{s}"]']
     else:
       receiving += make_export_wrappers(exports, delay_assignment)

src/settings.js

@@ -994,6 +994,14 @@ var EXPORTED_FUNCTIONS = [];
 // [link]
 var EXPORT_ALL = false;
 
+// If true, we export the symbols that are present in JS onto the Module
+// object.
+// It only does Module['X'] = X;
+//
+// This only applies to MINIMAL_RUNTIME, where symbols aren't exported by
+// default.
+var EXPORT_KEEPALIVE = true;
+
 // Remembers the values of these settings, and makes them accessible
 // through getCompilerSetting and emscripten_get_compiler_setting.
 // To see what is retained, look for compilerSettings in the generated code.