Bug 1918734 - Add preference for Math.sumPrecise proposal; r=dminor

Differential Revision: https://phabricator.services.mozilla.com/D224452

js/src/shell/js.cpp

@@ -12681,7 +12681,9 @@ bool InitOptionParser(OptionParser& op) {
                         "Enable WebAssembly tail-calls proposal.") ||
       !op.addBoolOption('\0', "wasm-js-string-builtins",
                         "Enable WebAssembly js-string-builtins proposal.") ||
-      !op.addBoolOption('\0', "enable-promise-try", "Enable Promise.try")) {
+      !op.addBoolOption('\0', "enable-promise-try", "Enable Promise.try") ||
+      !op.addBoolOption('\0', "enable-math-sumprecise",
+                        "Enable Math.sumPrecise")) {
     return false;
   }
 
@@ -12760,6 +12762,9 @@ bool SetGlobalOptionsPreJSInit(const OptionParser& op) {
   if (op.getBoolOption("enable-promise-try")) {
     JS::Prefs::setAtStartup_experimental_promise_try(true);
   }
+  if (op.getBoolOption("enable-math-sumprecise")) {
+    JS::Prefs::setAtStartup_experimental_math_sumprecise(true);
+  }
 #endif
   if (op.getBoolOption("enable-json-parse-with-source")) {
     JS::Prefs::set_experimental_json_parse_with_source(true);

modules/libpref/init/StaticPrefList.yaml

@@ -8102,6 +8102,13 @@
     mirror: always
     set_spidermonkey_pref: startup
 
+  # Experimental support for Math.sumPrecise in JavaScript.
+-   name: javascript.options.experimental.math_sumprecise
+    type: bool
+    value: false
+    mirror: always
+    set_spidermonkey_pref: startup
+
 #endif  // NIGHTLY_BUILD
 
 -   name: javascript.options.experimental.json_parse_with_source