JSAPI changes for ESR 153 Migration Guide

[arai-a]

Similar to #87 ,
this issue is for tracking the JSAPI changes we should mention in the migration guide for the next ESR release.

[arai-a]

Bug 1979652

JS::FinishCollectingDelazifications with a JS::TranscodeBuffer out parameter is going to be removed.
The exact same operation can be done with the following combination:

• JS::FinishCollectingDelazifications with a JS::Stencil out parameter, which just receives the JS::Stencil that reflects the collected delazifications
• JS::EncodeStencil which encodes the JS::Stencil into JS::TranscodeBuffer

// ==== ESR140 ====

RefPtr<JS::Stencil> stencil = ...;
JS::Rooted<JSScript*> script(cx, ...); // instantiate stencil

// Start.
if (!JS::StartCollectingDelazifications(cx, script, stencil, &alreadyStarted)) {
  return false;
}

// Finish and encode.
JS::TranscodeBuffer buffer;
if (!JS::FinishCollectingDelazifications(cx, script, buffer)) {
  return false;
}

// ==== ESR153 (also works on ESR140) ====

RefPtr<JS::Stencil> stencil = ...;
JS::Rooted<JSScript*> script(cx, ...); // instantiate stencil

// Start.
if (!JS::StartCollectingDelazifications(cx, script, stencil, &alreadyStarted)) {
  return false;
}

// Finish.
RefPtr<JS::Stencil> stencil2;
if (!JS::FinishCollectingDelazifications(cx, script, getter_AddRefs(stencil2))) {
  return false;
}

// NOTE: stencil == stencil2
// See https://bugzilla.mozilla.org/show_bug.cgi?id=1899090 for more details around the underlying structure change.

// Encode.
JS::TranscodeBuffer buffer;
JS::TranscodeResult result = JS::EncodeStencil(cx, stencil2, buffer);
if (result != JS::TranscodeResult::Ok) {
  return false;
}

[arai-a]

bug 1991370

JS::EncodeStencil will get JS::FrontendContext variant.
The existing JSContext variant is kept, so no change is necessary for the upgrade itself.

[arai-a]

bug 1768116

Now C++20-compatible compilers are necessary

[mgaudet]

Some job queue changes: https://spidermonkey.dev/blog/2026/01/15/job-responsibility.html

[ptomato]

That's an amazing blog post, you even did my work on GJS for me 🎉

[mgaudet]

cough it doesn't quite build, but I think the patch is at least the right shape :P