gh-136251: Improvements to WASM demo REPL - #136252

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ambv merged 23 commits into

python:mainfrom

Jul 21, 2025

adqm commented Jul 3, 2025•
edited by bedevere-app Bot
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I'm including a couple of fixes for the WASM demo, which for me made the demo "just work" out of the box for me with a build from following the instructions on this page:

Exported HEAPU32 at build time since python.worker.mjs expects it to be there (for determining the version number)
Updated the HTML to properly load xterm.js

I also made a few changes to try to improve the usability of the web REPL, also included here:

Reset things when starting a new process (without this change, running the same program multiple times would not work, requiring a refresh)
Added support for arrow key navigation (and home/end) in the REPL (including history scrollback)
Added support for TAB and CTRL+C, trying to mimic the behavior of the regular of those inputs from the Python REPL
Replaced the textarea with Ace code editor.
Moved the demo to index.html instead of python.html so that the URL shown in the terminal when running server.py takes you to the demo (without needing to append /python.html)

I also put up a demo here that shows the result of a fresh Emscripten build with these changes.

There's definitely still room for improvement here (for example, #124621 suggests updating the demo to use PyREPL), but I'm sharing these changes in case they're useful in the meantime.

Related Issue: #136251

Issue: Fixes and Improvements for Emscripten WASM REPL #136251

adqm requested review from corona10, erlend-aasland and freakboy3742 as code owners

July 3, 2025 17:43

python-cla-botBot commented Jul 3, 2025•
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Fixes and Improvements for Emscripten WASM REPL #136251

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bedevere-appBot commented Jul 3, 2025

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WASM REPL: update README.md to account for demo location moving

6d5f698

adqm requested a review from brettcannon as a code owner

July 3, 2025 17:52

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WASM REPL: add HEAPU32 to exports in configure.ac

16cfea2

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WASM REPL: fix for ACE setup in Chromium

faf2ba4

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sobolevn reviewed

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not a full review, just saw some style problems :)

Tools/wasm/emscripten/web_example/index.html Outdated

Tools/wasm/emscripten/web_example/index.html Outdated

Tools/wasm/emscripten/web_example/index.html Outdated

Tools/wasm/emscripten/web_example/index.html Outdated

brettcannon removed their request for review

July 3, 2025 21:01

WASM REPL: run prettier on index.html

70d4a17

bedevere-appBot commented Jul 3, 2025

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

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adqm commented Jul 3, 2025

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thanks, @sobolevn! i just ran prettier on that file; it looks like it caught those style issues and quite a few more.

WASM REPL: lower-case 'code' on 'Run code' button

ce5ebca

bedevere-appBot commented Jul 3, 2025

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

merwok reviewed

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Tools/wasm/emscripten/web_example/index.html Outdated

WASM REPL: make the magic ctrl+c string vary with each run

e06a7b2

hoodmane commented Jul 21, 2025

Contributor

I broke this on the main branch again (in one place I check for process incorrectly and cause a crash). In order to avoid breaking it we'll need to add an in-browser smoke test to the emscripten buildbot.

hoodmane added 2 commits

July 21, 2025 10:27

Merge branch 'main' into wasm_repl

3e76313

Fix emscripten in browser

26ddd07

hoodmane commented Jul 21, 2025

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Merged main and pushed a commit fixing the problem. I'll run the Emscripten buildbot on this and if it passes it is good to merge.

hoodmane commented Jul 21, 2025

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!buildbot emscripten

bedevere-bot commented Jul 21, 2025

🤖 New build scheduled with the buildbot fleet by @hoodmane for commit 26ddd07 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F136252%2Fmerge

The command will test the builders whose names match following regular expression: emscripten

The builders matched are:

WASM Emscripten PR

hoodmane commented Jul 21, 2025

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Okay it needs the fix from #136909 to unbreak the buildbot...

Merge branch 'main' into wasm_repl

7d33525

hoodmane commented Jul 21, 2025

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!buildbot emscripten

bedevere-bot commented Jul 21, 2025

🤖 New build scheduled with the buildbot fleet by @hoodmane for commit 7d33525 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F136252%2Fmerge

The command will test the builders whose names match following regular expression: emscripten

The builders matched are:

WASM Emscripten PR

ambv merged commit d1d526a into python:main

41 checks passed

bedevere-appBot removed the awaiting core review label

hoodmane added OS-emscripten topic-repl needs backport to 3.14 labels

miss-islington-appBot commented Jul 21, 2025

Thanks @adqm for the PR, and @ambv for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

miss-islington-appBot commented Jul 21, 2025

Sorry, @adqm and @ambv, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker d1d526afe7ce62c787b150652a2ba136cb949d74 3.14

miss-islington-appBot assigned ambv

hoodmane commented Jul 21, 2025

Contributor

Looks like first we have to backport #136822.

ambv added needs backport to 3.14 and removed needs backport to 3.14 labels

miss-islington-appBot commented Jul 22, 2025

Thanks @adqm for the PR, and @ambv for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request

pythongh-136251: Improvements to WASM demo REPL (pythonGH-136252)

cf7b7fe

(cherry picked from commit d1d526a)
Co-authored-by: adam j hartz <adam@smatz.net>
Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>

bedevere-appBot commented Jul 22, 2025

GH-136977 is a backport of this pull request to the 3.14 branch.

bedevere-appBot removed the needs backport to 3.14 label

ambv pushed a commit that referenced this pull request

[3.14]gh-136251: Improvements to WASM demo REPL (GH-136252) (GH-136977)

4f1f648

(cherry picked from commit d1d526a)
Co-authored-by: adam j hartz <adam@smatz.net>
Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>

taegyunkim pushed a commit to taegyunkim/cpython that referenced this pull request

pythongh-136251: Improvements to WASM demo REPL (pythonGH-136252)

265158f

Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>

Agent-Hellboy pushed a commit to Agent-Hellboy/cpython that referenced this pull request

pythongh-136251: Improvements to WASM demo REPL (pythonGH-136252)

d38c4bb

Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>

kumaraditya303 pushed a commit to miss-islington/cpython that referenced this pull request

[3.14]pythongh-136251: Improvements to WASM demo REPL (pythonGH-136252…

038755d

…) (pythonGH-136977)
(cherry picked from commit d1d526a)
Co-authored-by: adam j hartz <adam@smatz.net>
Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>

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