Make Emscripten aware of minimum browser versions for WASM_BIGINT setting (#17163)

When WASM_BIGINT is set, we can assume the browser is recent enough
to support that feature, as things will not work otherwise anyhow.

Author: hoodmane

ChangeLog.md

@@ -20,6 +20,8 @@ See docs/process.md for more on how version tagging works.
 
 3.2.0
 -----
+- Emscripten now knows what minimum browser versions the `WASM_BIGINT` feature
+  requires and will automatically set the defaults accordingly. (#17163)
 - Weak undefined symbols fixed in dynamic linking. (#17164)
 - Internally, the name of `main` function now gets mangled (by clang) in the
   same way as with other wasm targets.  This means that within the wasm module

emcc.py

@@ -396,6 +396,21 @@ def apply_settings(user_settings):
       settings.LTO = 0 if value else 'full'
 
 
+# apply minimum browser version defaults based on user settings. if
+# a user requests a feature that we know is only supported in browsers
+# from a specific version and above, we can assume that browser version.
+def apply_min_browser_versions(user_settings):
+
+  def default_min_browser_version(browser, version):
+    default_setting(user_settings, f'MIN_{browser.upper()}_VERSION', version)
+
+  if settings.WASM_BIGINT:
+    default_min_browser_version('Safari', 150000)
+    default_min_browser_version('Edge', 79)
+    default_min_browser_version('Firefox', 68)
+    # Chrome has BigInt since v67 which is less than default min version.
+
+
 def is_ar_file_with_missing_index(archive_file):
   # We parse the archive header outselves because llvm-nm --print-armap is slower and less
   # reliable.
@@ -2597,6 +2612,8 @@ def get_full_import_name(name):
   if settings.WASM_EXCEPTIONS:
     settings.REQUIRED_EXPORTS += ['__trap']
 
+  apply_min_browser_versions(user_settings)
+
   return target, wasm_target
 
 

src/settings.js

@@ -1338,9 +1338,10 @@ var WASM_ASYNC_COMPILATION = true;
 // [link]
 var DYNCALLS = false;
 
-// WebAssembly integration with JavaScript BigInt. When enabled we don't need
-// to legalize i64s into pairs of i32s, as the wasm VM will use a BigInt where
-// an i64 is used.
+// WebAssembly integration with JavaScript BigInt. When enabled we don't need to
+// legalize i64s into pairs of i32s, as the wasm VM will use a BigInt where an
+// i64 is used. If WASM_BIGINT is present, the default minimum supported browser
+// versions will be increased to the min version that supports BigInt.
 // [link]
 var WASM_BIGINT = false;