Warn of usage of legacy library symbols

emcc.py

@@ -664,6 +664,9 @@ def phase_parse_arguments(state):
   # warnings are properly printed during arg parse.
   newargs = diagnostics.capture_warnings(newargs)
 
+  if not diagnostics.is_enabled('deprecated'):
+    settings.WARN_DEPRECATED = 0
+
   for i in range(len(newargs)):
     if newargs[i] in ('-l', '-L', '-I', '-z'):
       # Scan for flags that can be written as either one or two arguments

src/library_legacy.js

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: MIT
  */
 
-addToLibrary({
+legacyFuncs = {
   $ALLOC_NORMAL: 0,  // Tries to use _malloc()
   $ALLOC_STACK: 1,  // Lives for the duration of the current function call
 
@@ -120,4 +120,18 @@ addToLibrary({
     });
   },
 #endif
-});
+};
+
+if (WARN_DEPRECATED && !INCLUDE_FULL_LIBRARY) {
+  for (const name of Object.keys(legacyFuncs)) {
+    if (!isDecorator(name)) {
+      depsKey = `${name}__deps`;
+      legacyFuncs[depsKey] = legacyFuncs[depsKey] || [];
+      legacyFuncs[depsKey].push(() => {
+        warn(`JS library symbol '${name}' is deprecated. Please open a bug if you have a continuing need for this symbol [-Wdeprecated]`);
+      });
+    }
+  }
+}
+
+addToLibrary(legacyFuncs);

src/settings_internal.js

@@ -273,3 +273,5 @@ var BULK_MEMORY = false;
 var MINIFY_WHITESPACE = true;
 
 var ASYNCIFY_IMPORTS_EXCEPT_JS_LIBS = [];
+
+var WARN_DEPRECATED = true;

test/test_core.py

@@ -7113,6 +7113,7 @@ def test(expected, args=None, assert_returncode=0):
 
     # Adding the symbol to DEFAULT_LIBRARY_FUNCS_TO_INCLUDE should allow direct usage, but
     # Module usage should continue to fail.
+    self.emcc_args += ['-Wno-deprecated']
     self.set_setting('DEFAULT_LIBRARY_FUNCS_TO_INCLUDE', ['$ALLOC_STACK'])
     test(not_exported, assert_returncode=NON_ZERO)
     test('1', args=['-DDIRECT'])

test/test_other.py

@@ -3670,11 +3670,11 @@ def test_exported_runtime_methods(self):
   def test_exported_runtime_methods_from_js_library(self):
     create_file('pre.js', '''
       Module.onRuntimeInitialized = () => {
-        Module.setErrNo(88);
+        out(Module.ptrToString(88));
         out('done');
       };
     ''')
-    self.do_runf('hello_world.c', 'done', emcc_args=['--pre-js=pre.js', '-sEXPORTED_RUNTIME_METHODS=setErrNo'])
+    self.do_runf('hello_world.c', 'done', emcc_args=['--pre-js=pre.js', '-sEXPORTED_RUNTIME_METHODS=ptrToString'])
 
   @crossplatform
   def test_fs_stream_proto(self):
@@ -13376,6 +13376,7 @@ def test_legacy_runtime(self):
 
     # By default `LEGACY_RUNTIME` is disabled and `allocate` is not available.
     self.set_setting('EXPORTED_RUNTIME_METHODS', ['ALLOC_NORMAL'])
+    self.emcc_args += ['-Wno-deprecated']
     self.do_runf('other/test_legacy_runtime.c',
                  '`allocate` is a library symbol and not included by default; add it to your library.js __deps or to DEFAULT_LIBRARY_FUNCS_TO_INCLUDE on the command line',
                  assert_returncode=NON_ZERO)