Complete the name of PostgreSQL databases

* lisp/progmodes/sql.el (sql-postgres-login-params): Complete database
name.
(sql-postgres-list-databases): New function returning a list of
available PostgreSQL databases.

* test/lisp/progmodes/sql-tests.el: New file with tests for sql.el.

lisp/progmodes/sql.el

@@ -1072,14 +1072,26 @@ add your name with a \"-U\" prefix (such as \"-Umark\") to the list."
   :version "20.8"
   :group 'SQL)
 
-(defcustom sql-postgres-login-params `((user :default ,(user-login-name))
-                                       (database :default ,(user-login-name))
-                                       server)
+(defcustom sql-postgres-login-params
+  `((user :default ,(user-login-name))
+    (database :default ,(user-login-name)
+              :completion ,(completion-table-dynamic
+                            (lambda (_) (sql-postgres-list-databases))))
+    server)
   "List of login parameters needed to connect to Postgres."
   :type 'sql-login-params
   :version "24.1"
   :group 'SQL)
 
+(defun sql-postgres-list-databases ()
+  "Return a list of available PostgreSQL databases."
+  (when (executable-find sql-postgres-program)
+    (let ((res '()))
+      (dolist (row (process-lines sql-postgres-program "-ltX"))
+        (when (string-match "^ \\([[:alnum:]-_]+\\) +|.*" row)
+          (push (match-string 1 row) res)))
+      (nreverse res))))
+
 ;; Customization for Interbase
 
 (defcustom sql-interbase-program "isql"

test/lisp/progmodes/sql-tests.el

@@ -0,0 +1,47 @@
+;;; sql-tests.el --- Tests for sql.el  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2016 Free Software Foundation, Inc.
+
+;; Author: Simen Heggestøyl <simenheg@gmail.com>
+;; Keywords:
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;
+
+;;; Code:
+
+(require 'cl-lib)
+(require 'ert)
+(require 'sql)
+
+(ert-deftest sql-tests-postgres-list-databases ()
+  "Test that output from `psql -ltX' is parsed correctly."
+  (cl-letf
+      (((symbol-function 'executable-find)
+        (lambda (_command) t))
+       ((symbol-function 'process-lines)
+        (lambda (_program &rest _args)
+          '(" db-name-1 | foo-user | UTF8     | en_US.UTF-8 | en_US.UTF-8 | "
+            " db_name_2 | foo-user | UTF8     | en_US.UTF-8 | en_US.UTF-8 | "
+            ""))))
+    (should (equal (sql-postgres-list-databases)
+                   '("db-name-1" "db_name_2")))))
+
+(provide 'sql-tests)
+;;; sql-tests.el ends here