Require at least Emacs 24.3 or properly support Emacs 24.1 and Emacs 24.2

[gracjan]

Currently haskell-mode claims compatibility with Emacs 24.1, this is not true.

Note that our test suite runs properly on both Emacs 24.1 and Emacs 24.2.

Support for Emacs 24.1/2 faces compilation warnings/errors:

• eval-after-load signals "Error: Attempt to modify read-only object"
• there are issues with cl package: function 'cl-find-if' from cl package called at runtime
• setq-local is absent

Fixable, but requires work.

So we have to decide and commit to one of the following:

1. Officially support Emacs 24.3 and greater.
2. Officially support Emacs 24.1/2 and add Travis tests for those.

Release dates for Emacs versions:

• Emacs 24.1: June 10, 2012
• Emacs 24.2: August 27, 2012
• Emacs 24.3: March 11, 2013
• Emacs 24.4: October 20, 2014
• Emacs 24.5: April 10, 2015

Ubuntu LTS 14.04 has Emacs 24.3 installed.

[gracjan]

Note: since c2hs we are using setq-local and nobody reported issues about it. This means people aren't using Emacs 23.2 or less.

[fice-t]

I happened to try the latest version out on 24.1 and it turns out Haskell Interactive mode doesn't work:

Debugger entered--Lisp error: (wrong-type-argument stringp #[257 "\300\301\302�!\"\207" [cl-find-if #[257 "\304�\305���\306�\307
    �#,\207" [start string regexp inhibit-changing-match-data ".\\.cabal\\'" nil t string-match] 5 "

I'd imagine being backwards compatible for a 3 year old version is good enough.

[gracjan]

@fice-t: This particular error might be there because your Emacs 24.1 used compiled versions of elc from Emacs 24.3.

[fice-t]

I don't believe so; I sandboxed the 24.1 version off. I found the .elc file responsible haskell-customize.elc and indeed it says ;;; in Emacs version 24.1.1.
Does haskell-interactive-mode work on your copy of 24.1?

[gracjan]

Okay, @fice-t, can you alter those places where we say we are Emacs 24 or 24.1 compatible and put 24.3 in there? Thanks.

[fice-t]

I could do that later. Should there be a new corresponding stable release with this?

[fice-t]

@gracjan Couple more questions:

1. Should haskell-mode error when on 24.1 and 24.2? Or perhaps just give a warning for those two versions as some parts work?
2. Should the cl-lib in the tests/compat directory be removed?

[fice-t]

@gracjan The work is basically done -- just need confirmation on the above.

[gracjan]

1. Error.
2. Remove cl-lib.

Rationale about 1: we either support things or we don't. If somebody wants to use haskell-mode with old versions they can always use one of old versions of haskell-mode.