* tools: make `v watch` build veb apps before restarting them
- Watch `templates/` and its subdirectories in veb projects. Templates are
compiled in, but the compiler does not report them, so a change to
`templates/layout/header.html` never triggered a rebuild.
- For veb apps, build the new executable while the old server keeps
serving, and swap them only when the build succeeds, so the app is down
only for the restart. A failed build leaves the old server running. A
change during a build cancels it and starts a new one, after a 150 ms
debounce. `--no-build-first` restores the previous behaviour.
- Write the build status (`building`, `failed` with the compiler output, or
`ok`) to a file named by VEB_LIVERELOAD_STATUS in the app's environment,
for veb's live reload. Print how long each build took.
- Stop the build and the program on SIGTERM and SIGHUP, as on Ctrl-C. They
run in their own process groups, so they kept running (and kept their
port) after `v watch` was terminated.
* veb: live reload over server-sent events, keeping page state
With `-d veb_livereload`:
- Replace the 250 ms polling with one Server-Sent Events stream per page,
held in a shared hub (no thread per tab), capped by
`-d veb_livereload_max_streams` (default 32). A keepalive ping every 15 s
drops closed tabs.
- After a restart, fetch the page again and morph the DOM in place, keeping
scroll position, focus, typed form values and page JS state. Pages from a
POST, failed fetches and non-HTML answers reload instead.
- Follow the files of a StaticHandler: a changed stylesheet is swapped in
place, other files update the page, with no rebuild.
- Relay the build status written by `v watch` (VEB_LIVERELOAD_STATUS): a
toast for rebuilding/updated, and a panel with the compiler output when a
build fails. `-d veb_livereload_no_toast` hides them.
- Reconnect every 250 ms; `-d veb_livereload_retry_max_ms` lets it back off.
- Keep the polling script behind `-d veb_livereload_polling`, for HTTPS apps
and for proxies that block long-lived connections, with its interval set
by `-d veb_livereload_poll_ms`. Deprecate the unused
`Context.livereload_poll_interval_ms`, which could never be set.
* examples, docs: update the veb live reload instructions
- examples/vwatch/web_server: put `-d veb_livereload` after `watch` (the
order before `watch` is currently dropped, see #30199), describe the new
live reload, and drop `--only-watch=*.v,*.html,*.css,*.js`, which is the
default for veb projects.
- v-veb skill: live reload is enabled by `-d veb_livereload` and applies to
any HTML response ending with `</html>`, not only to `$veb.html()` in
debug builds.
- veb blog tutorial: suggest `v watch -d veb_livereload run blog.v`, so the
open page updates too.
* veb: reload changed scripts and page resources
* veb: preserve typed values on their original form controls
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Co-authored-by: Alexander Medvednikov <alexander@medvednikov.com>
