vim automatic hard wrap for fortran with line-continuation - vim

Question

I'm a Fortran programmer who uses both free-form and fixed form. Since I have to mix them, usually I write code in a common form between free and fixed format, so in this way I can tell to vim that all my files are in the free format.
Vim is great in doing things like autoindentation, but I would like to type and let vim automatically wrap my code, and placing the Fortran continuation character & at column 73 (or greater), and at column 6 in the new line. Is it possible, or does it exist a plugin for this?
Currently I'm using textwidth=72 in fortran files to hard wrap the lines.
Thanks in advance.

Answer 1

One way to make vim insert text when going to a new line is to use formatexpr. Set it so to capture the line and replace it with itself with & and new line appended, when at/beyond a given column. In this case you are handling line breaks and textwidth does not apply. I didn't yet get to test some simple code for it, but here is a related example.
Another way would be to write general code so that when in a given column it inserts & and <CR>.
However, making any such approach respect Fortran-specific exclusions (comments, for one thing) will make it more complicated. The best solution would be to find suitable existing option(s) for Fortran, but I haven't so far.
This is a comment on indentation in general. It should allow you to directly set up a desired rule for a new line. Here is one standard set of files that set up a lot of indentation rules and features.
The usual entry point is this vim script, which requires another standard set of files. The link given on that page for the other files is broken though, so here is where to find them: unpack this zip file (found on this page), right into your ~/.vim/ directory. It will create subdirectories indent/, syntax/, and ftpplugin/, or put files into them if they exist, so be careful if you have stuff there already.
Then you can put the first script linked above into .vim/after/indent/. In this file, there are specific calculations of where to put the cursor when a new line is entered. Find the right place(s) and change to your desired indent, or preferably set up a snippet from it in another file (so not to change this file). In this case you also need to set things up so that it overrides settings from the first file.
A useful resource is indentexpr (or :help indentexpr).
Here is also a tutorial on that.
These are comments on syntax in general, posted initially. They contain items of help related to what you want and should be generally useful, but probably have not much to say about adding &.
There are plugins for fortran. Here is the syntax file, with many things to tweak.
This may already be on your system. (It was on mine.) Thus I would go through and pick and choose things to add to your .vimrc. Here are a few options that are directly related
syn match fortranContinueMark display "&"
syn sync linecont "&" minlines=20
Here are paragraphs that seem to me relevant in their entirety
if (b:fortran_fixed_source == 1)
if !exists("fortran_have_tabs")
"Flag items beyond column 72
syn match fortranSerialNumber excludenl "^.\{73,}$"lc=72
"Flag left margin errors
syn match fortranLabelError "^.\{-,4}[^0-9 ]" contains=fortranTab
syn match fortranLabelError "^.\{4}\d\S"
endif
syn match fortranComment excludenl "^[!c*].*$" contains=#fortranCommentGroup
syn match fortranLeftMargin transparent "^ \{5}"
syn match fortranContinueMark display "^.\{5}\S"lc=5
else
syn match fortranContinueMark display "&"
endif
if b:fortran_dialect != "f77"
syn match fortranComment excludenl "!.*$" contains=#fortranCommentGroup,#spell
endif
Then a block of syn match statements follow for common cpp-like settings, and then
"Synchronising limits assume that comment and continuation lines are not mixed
if exists("fortran_fold") || exists("fortran_more_precise")
syn sync fromstart
elseif (b:fortran_fixed_source == 0)
syn sync linecont "&" minlines=20
else
syn sync minlines=20
endif
By your question it appears that you know how to set up .vimrc but here are a few comments.
Syntax support need be enabled with appropriate enable and autogroup statements, for example
syntax enable
" au BufRead,BufNewFile *.f90 FileType=fortran
au FileType fortran setlocal ...
Here are some common formatting options that I have for fortran
autocmd FileType fortran setlocal formatoptions=croql comments=:/!/
There can also be a t among options, for textwidth
Here are some specific settings I have, which I see in this syntax file with far more sophistication
let fortran_free_source=1
" Said to need fortran.vim and/or fortran support packages (they work)
let fortran_do_enddo=1
let fortran_more_precise=1
Standard vim help is of course extensive, but try :help fortran -- it has a number of useful settings right up front and is not overwhelming at all. Also see ft-fortran-syntax from help.
See this post with some troubleshooting if things aren't working right. Here is another useful post, even as it appears unrelated by its title.