1464949 - Emacs "file variables" initial line dysfunctional in many files

Status: UNCONFIRMED

(Toolkit :: General, defect, P5)

Description

[plaice.adam+persona]

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0
Build ID: 20180517113820

Steps to reproduce:

Open toolkit/components/extensions/Schemas.jsm (https://dxr.mozilla.org/mozilla-central/source/toolkit/components/extensions/Schemas.jsm#1) in Emacs (e.g. version 24.5.1 or 26.1, without any customisations).

Any file with the initial line:

/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */

would also be affected.


Actual results:

The file was opened, but the specified file variables (indent-tabs-mode: nil, etc.) are not loaded and the following error messages are displayed:

Ignoring unknown mode ‘indent-tabs-mode: nil-mode’
Ignoring unknown mode ‘indent-tabs-mode:-mode’
Malformed mode-line: "nil; js-indent-level: 2"


Expected results:

The file is opened without any error messages and the specified file variables are loaded (indent-tabs-mode is set to nil, etc.)

This is obviously a very minor issue, only affecting developers/contributors using Emacs. OTOH the line:

/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */

is at the start of a couple of hundred files (≳ 200), while doing absolutely nothing (it does doesn't help Emacs users, nor users of other editors). It could be either removed (see also: https://bugzilla.mozilla.org/show_bug.cgi?id=1023839) or fixed, by changing it to:

/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */

or

/* -*- mode: js; indent-tabs-mode: nil; js-indent-level: 2 -*- */

(The latter, specifying the mode, is probably unnecessarily verbose, since Emacs is perfectly capable of determining the mode from the file extension.)