Remove basic_string<unsigned char> from embind (emscripten-core#23070)

Only `char`, `wchar`, `char8`, `char16`, and `char32` are valid
specializations for `std::basic_string`:
https://en.cppreference.com/w/cpp/string/basic_string

But libc++ had a base template for `basic_string` that allowed any type
to be passed for a long time. It looks there have been several attempts
to remove this after which they restored it due to complaints, in
chronological order:

llvm/llvm-project@aeecef0
llvm/llvm-project@08a0faf
llvm/llvm-project@e30a148
llvm/llvm-project#66153
llvm/llvm-project#72694

The last one, llvm/llvm-project#72694,
eventually removed it. So `std::basic_string<unsigned char>` is not
allowed anymore. This removes all uses of `std::basic_string<unsigned
char>` from embind.

This needs to be done to update libc++ to LLVM 19 (emscripten-core#22994). I'm
uploading this as a separate PR because this removes a functionality
from embind.

ChangeLog.md

@@ -26,6 +26,10 @@ See docs/process.md for more on how version tagging works.
 - Emscripten-generated code will now use async/await internally when loading
   the Wasm module.  This will be lowered away by babel when targeting older
   browsers. (#23068)
+- Due to the discontinued support for invalid specializations of
+- `std::basic_string` (https://github.com/llvm/llvm-project/pull/72694), the
+  support for `std::basic_string<unsigned char>` was removed from embind.
+  (#23070)
 
 3.1.73 - 11/28/24
 -----------------

src/embind/embind.js

@@ -496,8 +496,7 @@ var LibraryEmbind = {
     name = readLatin1String(name);
     var stdStringIsUTF8
 #if EMBIND_STD_STRING_IS_UTF8
-    //process only std::string bindings with UTF8 support, in contrast to e.g. std::basic_string<unsigned char>
-    = (name === "std::string");
+    = true;
 #else
     = false;
 #endif

system/lib/embind/bind.cpp

@@ -149,8 +149,6 @@ EMSCRIPTEN_BINDINGS(builtin) {
   register_float<double>("double");
 
   _embind_register_std_string(TypeID<std::string>::get(), "std::string");
-  _embind_register_std_string(
-    TypeID<std::basic_string<unsigned char>>::get(), "std::basic_string<unsigned char>");
   _embind_register_std_wstring(TypeID<std::wstring>::get(), sizeof(wchar_t), "std::wstring");
   _embind_register_std_wstring(TypeID<std::u16string>::get(), sizeof(char16_t), "std::u16string");
   _embind_register_std_wstring(TypeID<std::u32string>::get(), sizeof(char32_t), "std::u32string");

test/code_size/embind_hello_wasm.json

@@ -1,10 +1,10 @@
 {
   "a.html": 552,
   "a.html.gz": 380,
-  "a.js": 9718,
-  "a.js.gz": 4291,
-  "a.wasm": 7728,
-  "a.wasm.gz": 3502,
-  "total": 17998,
-  "total_gz": 8173
+  "a.js": 9593,
+  "a.js.gz": 4230,
+  "a.wasm": 7615,
+  "a.wasm.gz": 3471,
+  "total": 17760,
+  "total_gz": 8081
 }

test/code_size/embind_val_wasm.json

@@ -1,10 +1,10 @@
 {
   "a.html": 552,
   "a.html.gz": 380,
-  "a.js": 6849,
-  "a.js.gz": 2947,
-  "a.wasm": 9568,
-  "a.wasm.gz": 4911,
-  "total": 16969,
-  "total_gz": 8238
+  "a.js": 6724,
+  "a.js.gz": 2900,
+  "a.wasm": 9528,
+  "a.wasm.gz": 4896,
+  "total": 16804,
+  "total_gz": 8176
 }

test/embind/embind.test.js

@@ -449,33 +449,6 @@ module({
             assert.equal('ABCD', e);
         });
 
-        test("can pass Uint8Array to std::basic_string<unsigned char>", function() {
-            var e = cm.emval_test_take_and_return_std_basic_string_unsigned_char(new Uint8Array([65, 66, 67, 68]));
-            assert.equal('ABCD', e);
-        });
-
-        test("can pass long string to std::basic_string<unsigned char>", function() {
-            var s = 'this string is long enough to exceed the short string optimization';
-            var e = cm.emval_test_take_and_return_std_basic_string_unsigned_char(s);
-            assert.equal(s, e);
-        });
-
-        test("can pass Uint8ClampedArray to std::basic_string<unsigned char>", function() {
-            var e = cm.emval_test_take_and_return_std_basic_string_unsigned_char(new Uint8ClampedArray([65, 66, 67, 68]));
-            assert.equal('ABCD', e);
-        });
-
-
-        test("can pass Int8Array to std::basic_string<unsigned char>", function() {
-            var e = cm.emval_test_take_and_return_std_basic_string_unsigned_char(new Int8Array([65, 66, 67, 68]));
-            assert.equal('ABCD', e);
-        });
-
-        test("can pass ArrayBuffer to std::basic_string<unsigned char>", function() {
-            var e = cm.emval_test_take_and_return_std_basic_string_unsigned_char((new Int8Array([65, 66, 67, 68])).buffer);
-            assert.equal('ABCD', e);
-        });
-
         test("can pass string to std::string", function() {
             var string = stdStringIsUTF8?"aeiáéíαειЖЛФ從獅子€":"ABCD";
 

test/embind/embind_test.cpp

@@ -246,10 +246,6 @@ std::string emval_test_take_and_return_std_string_const_ref(const std::string& s
   return str;
 }
 
-std::basic_string<unsigned char> emval_test_take_and_return_std_basic_string_unsigned_char(std::basic_string<unsigned char> str) {
-  return str;
-}
-
 std::wstring take_and_return_std_wstring(std::wstring str) {
   return str;
 }
@@ -1914,7 +1910,6 @@ EMSCRIPTEN_BINDINGS(tests) {
   //function("emval_test_take_and_return_const_char_star", &emval_test_take_and_return_const_char_star);
   function("emval_test_take_and_return_std_string", &emval_test_take_and_return_std_string);
   function("emval_test_take_and_return_std_string_const_ref", &emval_test_take_and_return_std_string_const_ref);
-  function("emval_test_take_and_return_std_basic_string_unsigned_char", &emval_test_take_and_return_std_basic_string_unsigned_char);
   function("take_and_return_std_wstring", &take_and_return_std_wstring);
   function("take_and_return_std_u16string", &take_and_return_std_u16string);
   function("take_and_return_std_u32string", &take_and_return_std_u32string);