refactor(external-open): consolidate OS-open dispatch in external-open.el

Phase 4 of utility-consolidation. Three previously-overlapping helpers (system-utils' `cj/identify-external-open-command' and `cj/--open-with-is-launcher-p', plus the dirvish-only `cj/--file-manager-program-for' shipped earlier today) all answered "which OS-open program should I run?".  Pull the answer into one place: external-open.el.

Move and rename:

- `cj/--open-with-is-launcher-p' (system-utils) -> `cj/external-open-launcher-p' (external-open). Public name now matches its module.
- `cj/identify-external-open-command' (system-utils) -> `cj/external-open-command' (external-open). Returns nil for unsupported hosts instead of signaling -- callers that need a command must handle nil explicitly. The wrapper `cj/xdg-open' (also moved into external-open) converts nil to a `user-error' with a clear message, preserving the user-facing failure shape.
- Delete dirvish's `cj/--file-manager-program-for' helper. `cj/dirvish-open-file-manager-here' now calls `cj/external-open-command' directly. The shell-command fallback for nil-program preserves the previous escape hatch.

Break the system-utils <-> external-open recursive require by moving `cj/xdg-open' (the only system-utils function that external-open used) into external-open along with the dispatch.

Tests reorganized to match the move. Two new test files (`test-external-open-command.el', `test-external-open-launcher-p.el') replace the two system-utils-named test files. The dirvish file-manager-program test goes away with the helper. 11 tests covering Normal/Boundary/Error for the dispatch (plus the new "unsupported host returns nil" contract).

Add `(require \='external-open)' to system-utils.el and `(require \='system-lib)' to external-open.el (for `cj/file-from-context' which xdg-open uses).

1 files changed, 0 insertions, 59 deletions

diff --git a/tests/test-system-utils-identify-external-open-command.el b/tests/test-system-utils-identify-external-open-command.el
deleted file mode 100644
index dc272570..00000000
--- a/tests/test-system-utils-identify-external-open-command.el
+++ /dev/null
@@ -1,59 +0,0 @@
-;;; test-system-utils-identify-external-open-command.el --- Tests for cj/identify-external-open-command -*- lexical-binding: t; -*-
-
-;;; Commentary:
-;; Unit tests for `cj/identify-external-open-command' in system-utils.el.
-;; The function dispatches on host-environment predicates to return the
-;; appropriate "open" command: xdg-open on Linux, open on macOS,
-;; start on Windows.  Anything else is a fatal error.
-
-;;; Code:
-
-(require 'ert)
-(require 'cl-lib)
-
-(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
-(require 'system-utils)
-
-(defmacro test-siuec--with-host (linux macos windows &rest body)
-  "Run BODY with env-*-p predicates stubbed to LINUX, MACOS, WINDOWS."
-  (declare (indent 3))
-  `(cl-letf (((symbol-function 'env-linux-p)   (lambda () ,linux))
-			 ((symbol-function 'env-macos-p)   (lambda () ,macos))
-			 ((symbol-function 'env-windows-p) (lambda () ,windows)))
-	 ,@body))
-
-;;; Normal cases
-
-(ert-deftest test-siuec-linux-returns-xdg-open ()
-  "Normal: Linux host returns \"xdg-open\"."
-  (test-siuec--with-host t nil nil
-	(should (string= "xdg-open" (cj/identify-external-open-command)))))
-
-(ert-deftest test-siuec-macos-returns-open ()
-  "Normal: macOS host returns \"open\"."
-  (test-siuec--with-host nil t nil
-	(should (string= "open" (cj/identify-external-open-command)))))
-
-(ert-deftest test-siuec-windows-returns-start ()
-  "Normal: Windows host returns \"start\"."
-  (test-siuec--with-host nil nil t
-	(should (string= "start" (cj/identify-external-open-command)))))
-
-;;; Boundary cases
-
-(ert-deftest test-siuec-dispatch-order-linux-wins ()
-  "Boundary: Linux check runs first; wins when predicates disagree.
-Documents the dispatch order.  A real host only returns t from one
-of these anyway — but if something goes wrong, Linux takes priority."
-  (test-siuec--with-host t t t
-	(should (string= "xdg-open" (cj/identify-external-open-command)))))
-
-;;; Error cases
-
-(ert-deftest test-siuec-unsupported-host-signals-error ()
-  "Error: when no platform predicate returns non-nil, signals an error."
-  (test-siuec--with-host nil nil nil
-	(should-error (cj/identify-external-open-command))))
-
-(provide 'test-system-utils-identify-external-open-command)
-;;; test-system-utils-identify-external-open-command.el ends here