Make flycheck-phpstan a generic checker, add Apple container support

[zonuexe]

Replaces the executable injection in flycheck-phpstan with a Flycheck generic checker, adds Apple container support, and fixes three bugs found on the way.

Why

flycheck-define-checker requires the car of :command to be a literal string, and the program can only be overridden through the single string variable flycheck-CHECKER-executable. PHPStan does not fit that shape: phpstan-executable may expand to a whole command line such as docker run --rm -v ...:/app IMAGE, chosen per project.

So the checker declared a dummy "php" executable, overwrote flycheck-phpstan-executable as a side effect of its :enabled predicate, and had phpstan-get-command-args omit the program so flycheck would prepend the injected one.

:start now builds the command from phpstan-executable with :include-executable t — the same call flymake-phpstan already makes — and reports errors through the status callback. No dummy executable, no variable injection, and no :around advice on flycheck-finish-checker-process.

Bugs fixed

All three were confirmed by execution, not by reading:

1. phpstan-get-command-args destructively modified its inputs. It built the result with nconc, but two of the lists it links are owned by the caller. With (phpstan-executable . ("docker" "run" ...)) the variable grew by seven elements per check (6 → 13 → 20 → 27), and each M-x phpstan-generate-baseline appended another "--" to the phpstan-generate-baseline-options defcustom.

2. The (STRING . (ARGUMENTS ...)) form dropped the command name. It returned (cdr phpstan-executable), so ("docker" "run" ...) ran run as the program. This broke flymake-phpstan and phpstan-analyze-project, and made flycheck-phpstan set its executable to "run".

3. Flycheck could get stuck. The advice that suppressed "No files found to analyse" in a modified buffer worked by not calling the wrapped function at all, so no status was ever reported. As flycheck-report-buffer-checker-status documents, a checker that never reports a finishing status leaves flycheck stuck on the current check — silently killing checking for that buffer. It now finishes with an empty result.

Dropping the dummy "php" also fixes a fourth: Flycheck wraps :enabled so that flycheck-find-checker-executable runs before the checker's own predicate, resolving "php" against exec-path while the injected variable was still nil. A Docker-only setup with no local php could never enable the checker.

Apple container

phpstan-executable accepts container. Apple container runs the same OCI images with the same run --rm -v HOST:/app IMAGE command line as Docker, so only the command name differs; the image still comes from phpstan-docker-image.

The existing docker handling conflated two questions, so this splits them:

• phpstan--container-runtime-command — should phpstan.el build a run command line? Only the symbol forms say yes; (STRING . (ARGUMENTS ...)) already supplies a complete command line and must not be rewritten.
• phpstan--container-executable-p — does PHPStan see the project through a mount point, so phpstan-normalize-path must rewrite paths to /app? Also true for ("docker" "run" ...).

Verification

Ran Flycheck for real against local PHPStan 1.12.33, for both an unmodified buffer (analyzes the original) and a modified one (editor mode via --tmp-file): errors reported correctly, no leftover temporaries, checker never stuck. container run was executed directly against the phpstan image and returns the same output as Docker. Each commit byte-compiles on its own.

Known issue, not fixed here

Docker and Apple container do not work through Flycheck, and did not before this PR either (verified against the original code). The analyzed source path is passed to the container unnormalized — the config file becomes -c /app/tests/phpstan-docker.neon correctly, but the target file stays a host path, so PHPStan reports Path /Users/... does not exist and returns zero errors. flymake-phpstan avoids this by calling phpstan-normalize-path itself.

Related: phpstan-editor-mode-available-p runs docker --version and parses d1c06ef out of Docker version 29.5.3, build d1c06ef as the PHPStan version, so editor mode is silently disabled for container users.

Both are independent of this refactor and need their own design decisions (forcing in-place temp files inside the mount; how to version-check PHPStan inside a container), so they are left for follow-ups.

Compatibility

phpstan-flycheck-auto-set-executable is obsolete and ignored (make-obsolete-variable, 0.10.0). flycheck-phpstan-executable is gone; it was an undocumented bare defvar that the package set itself, not a user-facing knob.