Add warning about usage of embind without C++17 (#25424)

See #24850

Author: sbc100

ChangeLog.md

@@ -20,6 +20,7 @@ See docs/process.md for more on how version tagging works.
 
 4.0.16 (in development)
 -----------------------
+- A warning was added about usage of embind without C++17 or above. (#25424)
 - The minimum supported versions of Node, Chrome and Firefox were bumped
   enabling the removal of the `globalThis` polyfill and universally enabling
   mutable globals: (#25375, #25385)

system/include/emscripten/bind.h

@@ -7,10 +7,6 @@
 
 #pragma once
 
-#if __cplusplus < 201103L
-#error Including <emscripten/bind.h> requires building with -std=c++11 or newer!
-#endif
-
 #include <cassert>
 #include <cstddef>
 #include <functional>

system/include/emscripten/val.h

@@ -7,10 +7,6 @@
 
 #pragma once
 
-#if __cplusplus < 201103L
-#error Including <emscripten/val.h> requires building with -std=c++11 or newer!
-#endif
-
 #include <cassert>
 #include <array>
 #include <climits>

system/include/emscripten/wire.h

@@ -8,7 +8,11 @@
 #pragma once
 
 #if __cplusplus < 201103L
-#error Including <emscripten/wire.h> requires building with -std=c++11 or newer!
+#error "embind requires -std=c++11 or newer"
+#endif
+
+#if __cplusplus < 201703L
+#warning "embind is likely moving to c++17 (https://github.com/emscripten-core/emscripten/issues/24850)"
 #endif
 
 // A value moving between JavaScript and C++ has three representations:

test/test_other.py

@@ -3328,7 +3328,7 @@ def test_embind_no_raw_pointers(self, filename):
     # With no arguments we are effectively testing c++17 since it is the default.
     '': [],
     # Ensure embind compiles under C++11 which is the miniumum supported version.
-    'cxx11': ['-std=c++11'],
+    'cxx11': ['-std=c++11', '-Wno-#warnings'],
     'o1': ['-O1'],
     'o2': ['-O2'],
     'o2_mem_growth': ['-O2', '-sALLOW_MEMORY_GROWTH', test_file('embind/isMemoryGrowthEnabled=true.cpp')],
@@ -3377,6 +3377,14 @@ def test_embind(self, *extra_args):
     output = self.run_js(js_file)
     self.assertNotContained('FAIL', output)
 
+  def test_embind_cxx11_warning(self):
+    err = self.run_process([EMXX, '-c', '-std=c++11', test_file('embind/test_unsigned.cpp')], stderr=PIPE).stderr
+    self.assertContained('#warning "embind is likely moving to c++17', err)
+
+  def test_embind_cxx03(self):
+    err = self.expect_fail([EMXX, '-c', '-std=c++03', test_file('embind/test_unsigned.cpp')])
+    self.assertContained('#error "embind requires -std=c++11 or newer"', err)
+
   @requires_node
   def test_embind_finalization(self):
     self.run_process(