[Fix #1044] Prefer call-process to shell-command-to-string (#1045)

This change makes it so that a direct `call-process` invocation is used
when it is possible to determine what binary should be used for the
command. This avoids the cost of shell startup time that is incurred
when `shell-command-to-string` is invoked instead.

.gitignore

@@ -1,6 +1,7 @@
 /elpa
+/.elpa
 /.cask
 *.elc
 *~
 [#]*[#]
-/TAGS
+/TAGS

CHANGELOG.md

@@ -60,7 +60,9 @@
 * [#576](https://github.com/bbatsov/projectile/issues/576): `projectile-replace` stomps regular expressions.
 * [#957](https://github.com/bbatsov/projectile/pull/957): When opening a specified file from the terminal, do not error inside of `projectile-cache-current-file`.
 * [#984](https://github.com/bbatsov/projectile/pull/984): Error when a project is a symlink that changes target.
+
 * [#1013](https://github.com/bbatsov/projectile/issues/1013): `projectile-project-buffer-p` may return incorrect result on Windows.
+* [#1044](https://github.com/bbatsov/projectile/issues/1044): Replace `shell-command-to-string` invocations with `call-process` invocations where possible to avoid shell startup cost.
 
 ## 0.13.0 (2015-10-21)
 

Cask

@@ -6,4 +6,5 @@
 (development
  (depends-on "noflet")
  (depends-on "helm")
- (depends-on "ag"))
+ (depends-on "ag")
+ (depends-on "el-mock"))

projectile.el

@@ -37,11 +37,12 @@
 ;;; Code:
 
 (require 'cl-lib)
-(require 'thingatpt)
-(require 'ibuffer)
-(require 'ibuf-ext)
 (require 'compile)
+(require 'eshell)
 (require 'grep)
+(require 'ibuf-ext)
+(require 'ibuffer)
+(require 'thingatpt)
 
 (eval-when-compile
   (defvar ag-ignore-list)
@@ -1075,9 +1076,29 @@ they are excluded from the results of this function."
     (when cmd
       (projectile-files-via-ext-command cmd))))
 
+(defun projectile-call-process-to-string (program &rest args)
+  "Invoke the executable PROGRAM with ARGS and return the output as a string."
+  (with-temp-buffer
+     (apply 'call-process program nil (current-buffer) nil args)
+     (buffer-string)))
+
+(defun projectile-shell-command-to-string (command)
+  "Try to run COMMAND without actually using a shell and return the output.
+
+The function `eshell-search-path' will be used to search the PATH
+environment variable for an appropriate executable using the text
+occuring before the first space. If no executable is found,
+fallback to `shell-command-to-string'"
+  (cl-destructuring-bind
+      (the-command . args) (split-string command " ")
+    (let ((binary-path (eshell-search-path the-command)))
+      (if binary-path
+          (apply 'projectile-call-process-to-string binary-path args)
+        (shell-command-to-string command)))))
+
 (defun projectile-files-via-ext-command (command)
   "Get a list of relative file names in the project root by executing COMMAND."
-  (split-string (shell-command-to-string command) "\0" t))
+  (split-string (projectile-shell-command-to-string command) "\0" t))
 
 (defun projectile-index-directory (directory patterns progress-reporter)
   "Index DIRECTORY taking into account PATTERNS.

test/projectile-test.el

@@ -717,6 +717,27 @@
         (should (equal (list (expand-file-name "vendor/client-submodule/" project))
                        (projectile-get-all-sub-projects project)))))))
 
+(ert-deftest projectile-test-projectile-shell-command-to-string-fallback ()
+  (let ((command "command arg1 arg2")
+        (command-path "/path/to/command")
+        shell-command-args call-process-args)
+    (noflet ((shell-command-to-string (&rest args)
+                                      (setq shell-command-args args))
+             (call-process (&rest args)
+                           (setq call-process-args args)))
+      (noflet ((eshell-search-path (_command) nil))
+        (projectile-shell-command-to-string command)
+        (should (equal shell-command-args (list command)))
+        (should (equal call-process-args nil)))
+      (setq shell-command-args nil
+            call-process-args nil)
+      (noflet ((eshell-search-path (_command-name) command-path))
+        (projectile-shell-command-to-string command)
+        (should (equal shell-command-args nil))
+        (should (equal (car call-process-args) command-path))
+        (should (equal (-slice call-process-args 4)
+                       (cdr (split-string command " "))))))))
+
 ;; Local Variables:
 ;; indent-tabs-mode: nil
 ;; End: