Display a useful error message when PL/pgSQL is not available

Change-Id: Ib9a72a9e36bb24da5907720242b23e991bb7bf9a
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>

htdocs/lang/en.utf8/error.php

@@ -70,6 +70,7 @@ The error received was:
 ';
 $string['dbnotutf8'] = 'You are not using a UTF-8 database. Mahara stores all data as UTF-8 internally. Please drop and re-create your database using UTF-8 encoding.';
 $string['dbversioncheckfailed'] = 'Your database server version is not new enough to successfully run Mahara. Your server is %s %s, but Mahara requires at least version %s.';
+$string['plpgsqlnotavailable'] = 'The PL/pgSQL language is not enabled in your Postgres installation, and Mahara cannot enable it.  Please install PL/pgSQL using the CREATE LANGUAGE command, or the createlang program.';
 
 // general exception error messages
 $string['blocktypenametaken'] = "Block type %s is already taken by another plugin (%s)";

htdocs/lib/dml.php

@@ -1688,3 +1688,23 @@ function db_interval($s) {
         return "INTERVAL $s SECOND";
     }
 }
+
+function postgres_language_exists($language) {
+    if (!is_postgres()) {
+        throw new SQLException('postgres_language_exists() expects a postgres database');
+    }
+    return get_field_sql('SELECT 1 FROM pg_catalog.pg_language WHERE lanname = ?', array($language)) == 1;
+}
+
+function postgres_create_language($language) {
+    if (!is_postgres()) {
+        throw new SQLException('postgres_create_language() expects a postgres database');
+    }
+
+    // CREATE LANGUAGE fails if the language already exists
+    if (postgres_language_exists($language)) {
+        return true;
+    }
+    execute_sql("CREATE LANGUAGE $language;");
+    return postgres_language_exists($language);
+}

htdocs/lib/mahara.php

@@ -180,6 +180,9 @@ function ensure_install_sanity() {
     if (!db_is_utf8()) {
         throw new ConfigSanityException(get_string('dbnotutf8', 'error'));
     }
+    if (is_postgres() && !postgres_create_language('plpgsql')) {
+        throw new ConfigSanityException(get_string('plpgsqlnotavailable', 'error'));
+    }
 }
 
 function ensure_upgrade_sanity() {
@@ -192,6 +195,9 @@ function ensure_upgrade_sanity() {
             }
         }
     }
+    if (is_postgres() && !postgres_create_language('plpgsql')) {
+        throw new ConfigSanityException(get_string('plpgsqlnotavailable', 'error'));
+    }
 }
 
 /**