Detect restrictive OS-level ulimit -v and warn in wp cli info - #6397

Summary

Fixes #6326.

Reports on that issue trace back to mmap() failed: [12] Cannot allocate memory errors happening on shared/cPanel hosting even though PHP's memory_limit is generous (e.g. 748M) and the site itself runs fine. As one commenter on the issue put it: "I think it is ulimit limiting it. No graceful fallback if ulimit memory limit kills the process?"

That diagnosis is correct. On these hosts, the shell/SSH jail enforces an OS-level ulimit -v (RLIMIT_AS, total virtual address space) that is independent of and often much lower than PHP's memory_limit. When PHP's Zend memory manager tries to mmap() a new memory chunk, the OS refuses well before memory_limit is ever reached, and the process aborts with the cryptic mmap() failed message. Raising memory_limit does nothing in this situation, which is exactly the dead end users hit in the issue thread.

This PR does not attempt to work around the OS constraint itself (that's not something a userland PHP process can safely do), but it makes the real cause visible instead of leaving users guessing:

• wp cli info (and its --format=json output) now also reports the shell's ulimit -v value, alongside the existing memory_limit line.
• The existing low-memory-limit check in wp cli info is extended to also warn when the detected ulimit -v is more restrictive than PHP's memory_limit, explicitly calling out that increasing memory_limit won't help and that the OS-level limit needs to be raised instead.
• Detection is a plain ulimit -v shell query (rlimits are inherited by child processes, so it reflects the limit already in effect for the running PHP process); it degrades to n/a/no-op on Windows or if shell_exec is unavailable, so there's no behavior change for environments without this constraint.

Reproducing the original issue

Using Docker to simulate the reporter's environment (memory_limit=748M, restrictive ulimit -v):

$ docker run --rm php:8.2-cli sh -c "ulimit -v 65536; php -d memory_limit=748M -r '\$a = str_repeat(\"x\", 200*1024*1024);'"
Fatal error: Out of memory (allocated 2097152 bytes) (tried to allocate 209715232 bytes) in Command line code on line 1
mmap() failed: [12] Cannot allocate memory
mmap() failed: [12] Cannot allocate memory

Running the patched wp cli info in the same shell now surfaces the actual cause up front:

PHP memory limit:	748M
OS virtual memory limit (ulimit -v):	64M
...
Warning: This shell's OS-level virtual memory limit (`ulimit -v`) is set to 64M, which is lower than PHP's memory limit (748M). This is a common cause of "mmap() failed: Cannot allocate memory" errors even though memory_limit itself looks sufficient. Increasing memory_limit will not help; ask your hosting provider to raise the OS-level limit instead.

Test plan

• Added unit tests in tests/CLICommandTest.php covering format_kilobytes() and the new/extended check_memory_limit() branches (low memory_limit only, sufficient memory_limit, unknown/unlimited ulimit, restrictive ulimit vs. finite memory_limit, restrictive ulimit vs. unlimited memory_limit, ulimit higher than memory_limit).
• Added a Behat scenario in features/cli-info.feature asserting the new OS virtual memory limit line/field appears in both text and JSON output of wp cli info.
• composer phpunit — full suite passes (532 tests).
• composer phpcs — clean.
• vendor/bin/phpstan analyse ... --memory-limit=1G — no new errors (pre-existing, unrelated method.deprecated baseline mismatches on this PHP version are present identically on main).
• Manually reproduced the original mmap() failed error via Docker with a restrictive ulimit -v and confirmed the new warning correctly identifies the root cause (see above).
• Ran wp cli info / wp cli info --format=json locally via bin/wp to confirm normal (unrestricted) output is unaffected.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • wp cli info now displays the operating system’s virtual memory limit in human-readable and JSON output.
  • Memory diagnostics now identify when operating system or PHP limits may restrict available memory.
• Bug Fixes
  • Improved memory-limit warnings for low, restrictive, unlimited, or unavailable limits.
  • Memory values are formatted more clearly for display.
  • Warnings now indicate when the operating system’s virtual memory limit is lower than PHP’s configured memory limit.