Adding comments in middle of a line

[travisdowns]

I'm not sure if this is a nasm-mode issue, or just a quirk of emacs comment handling, but when using the nasm mode, I can no longer add a ; character in the middle of a line.

For example, I often have something like:

xor eax, dword [ebx + ecx + 123]

and I want to comment out everything after and including dword, like:

xor eax, ebx ; dword [ebx + ecx + 123]

When I enter the ; in that location there, the cursor instead jumps to the end of the line and adds the ; there. In some cases this is helpful, but in this case not. I have to delete everything I want to comment out, and then write the comment.

nasm-mode issue or emacs quirk?

[skeeto]

This is by design. The ";" key is bound to nasm-comment. The function's
documentation explains all the behavior. You could rebind ";" to
self-insert-command to get simple behavior back. Or on a case-by-case
basis, you could do a literal insertion with "C-q ;".

I did this because assembly tends of have lots of gutter comments, and
this behavior felt natural to me.

[travisdowns]

OK, thanks! I guess C-q ; is what I was looking for, since the nasm-comment behavior is often useful as you point out (but sometimes I need the literal insertion). I didn't even think to read the function doc, but I'm a returning emacs user and it's coming back slowly.

BTW, what's a gutter comment? Google failed me here...

Feel free to close this issue, of course.

[skeeto]

Considering that this doesn't show up in a Google search (I just tried
it myself), perhaps I'm using the wrong term. What I mean is the
right-hand column of comments often found in assembly listings. That's
where it jumps when you hit ";" in certain circumstances.

[travisdowns]

Makes sense. BTW is there any place the mode is documented that I should be reading (outside of the blog post that introduced it), or should I rely mostly on in-emacs docs?

[lassik]

The main reference for this stuff is the Comment Commands section in the Emacs manual.

The Emacs term for gutter comments seems to be right-margin comments. I got that from the docstring of the comment-column variable which sets the position of the right margin. nasm-mode implicitly uses that setting by calling comment-indent.

The standard behavior is for ; to be a normal self-inserting character and for M-; to have "magic" behavior. M-; is globally bound to the command comment-dwim (it already works in nasm-mode as well, mostly as intended). It does something very similar to the special-purpose nasm-comment command that is bound to ;.

Here's a comparison of M-; to the current nasm-comment command:

• If no comment gutter exists yet, mark the current position and jump to it.

M-; does this (except it doesn't mark the current position).

• If already within the gutter, pop the top mark and return to the code.

This is the one thing that M-; doesn't do - if you press it while inside a comment, it jumps to the beginning of the comment, not back to the code. I couldn't find a standard command to jump back to the code.

• If on a line with no code, just insert a comment character.

M-; does this. (On blank lines the comment is not indented to the right margin by default, but is fixed by the code below.)

• If within the indentation, just insert a comment character. This is intended prevent interference when the intention is to comment out the line.

This is usually done by just typing ;.

With a prefix arg, kill the comment on the current line with `comment-kill'."

M-; does this.

I tried to fix the behavior of M-; for NASM and here's the code:

(defun nasm-comment-indent ()
  comment-column)

(defun nasm-insert-comment ()
  (let ((comment-insert-comment-function nil))
    (comment-indent)))

And this to set buffer-local variables after entering nasm-mode:

(setq comment-indent-function 'nasm-comment-indent
      comment-insert-comment-function 'nasm-insert-comment)

What do you think about adopting this convention?

I also faintly recall there being a standard setting for an "electric" semicolon that auto-indents comments instead of self-inserting, but I can't find it now. I think at least Emacs Lisp mode had it on by default in some version of Emacs and that surprised me.

While trying this out, I realized that nasm-indent-line re-indents a comment on an otherwise-blank line to statement level, not to the right margin. I'm not sure whether you consider this a bug.

Sorry about the long-winded post. I thought to just leave a quick remark but ended up spending way too much time on it...

[lassik]

I packaged up the above code in PR #11 in any case since it improves M-; without breaking anything.

[skeeto]

While trying this out, I realized that nasm-indent-line re-indents a comment on an otherwise-blank line to statement level, not to the right margin. I'm not sure whether you consider this a bug.

Yeah, I think that's a bug.