PHP: Support read() from a blocking pipe

[adamziel]

Shims read(2) functionallity by providing an alternative read()
function called wasm_read() that gracefully handles blocking
pipes. This is neecessary because Emscripten returns EWOULDBLOCK
when reading from a blocking pipe, whereas a clang-compiled
program would wait until data becomes available.

See:

• PHP: Make proc_open work without requiring an explicit sleep() #951
• pipe() doesn't create a blocking pipe emscripten-core/emscripten#13214

Other changes

This PR also ships:

• A regexp fix for @php-wasm/cli to preserve a trailing whitespace when rewrite PHP-related spawn shell commands.
• A fix to correctly propagate the child process exit code back to PHP. The WordPress bootstrap script for PHPUnit needs that to work correctly.

Motivation

wp-cli

Without this PR, running wp-cli.phar doesn't output anything. The output is piped through a pager like less using proc_open and then displayed by reading from a blocking pipe.

With this PR, running wp-cli.phar returns its regular help message as the pager pipe can be read:

NAME
  wp
DESCRIPTION
  Manage WordPress through the command-line.
SYNOPSIS
  wp <command>
SUBCOMMANDS
  cache                 Adds, removes, fetches, and flushes the WP Object Cache
                        object.
  cap                   Adds, removes, and lists capabilities of a user role.
  cli                   Reviews current WP-CLI info, checks for updates, or
                        views defined aliases.
...

PHPUnit

With this PR, Playground can run PHPunit on wordpress-develop!

TMPDIR=/tmp PHP=8.2 node --loader ../plugins/playground/packages/nx-extensions/src/executors/built-script/loader.mjs ../plugins/playground/dist/packages/php-wasm/cli/main.js ./vendor/bin/phpunit --no-coverage -v
(node:87723) ExperimentalWarning: Custom ESM Loaders is an experimental feature. This feature could change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
Installing...
aaabb
int(0)
Running as single site... To run multisite, use -c tests/phpunit/multisite.xml
Not running ajax tests. To execute these, use --group ajax.
Not running ms-files tests. To execute these, use --group ms-files.
Not running external-http tests. To execute these, use --group external-http.
PHPUnit 9.6.15 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.2.10-dev
Configuration: /Users/cloudnik/www/Automattic/core/wordpress-develop/phpunit.xml.dist
Warning:       Your XML configuration validates against a deprecated schema.
Suggestion:    Migrate your XML configuration using "--migrate-configuration"!

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Testing instructions

Confirm the proc_open() tests pass on CI. This PR adjusts a few
of them to make sure the output is read without the tricky sleep()
call.

Related:

• Support wp-cli #827
• proc_open method takes an array or a string as first parameter  #930

CC @mho22

[adamziel]

Relevant explorations: #951 (comment)

[dmsnell]

😄

what actually happens if we do timeout letting this run indefinitely? will the PHP process run its own timeout? if that's the case, is it safe to let this block forever?

[adamziel]

Aha, good spot. Yes, I think we're good to just let this block until PHP times out.

[adamziel]

Actually, this may block a PHPUnit test suite without any visible feedback so I think we have to give up eventually. It's a shame, I'd rather rely on PHP timeout.

[adamziel]

One remaining issue is reading from a blocking file pipe as opposed to just a process pipe.