How to un-silent exec in vim only if there is an error?

Question

I have a few hotkeys mapped in my .vimrc (see below) for compiling and running autohotkey scripts but I can either be annoyed by the quest for the any key or I can run them silent and be unaware if there are errors.

autocmd filetype autohotkey nnoremap <S-F5> :w <bar> silent exec '!"C:\Program Files\AutoHotkey\Compiler\Ahk2Exe.exe" /in '.shellescape('%')<CR>
autocmd filetype autohotkey nnoremap <C-F5> :w <bar> silent exec '!"C:\Program Files\AutoHotkey\Compiler\Ahk2Exe.exe" /in '.shellescape('%').' && start .\'.shellescape('%:r')<CR>
autocmd filetype autohotkey nnoremap <S-F6> :silent exec '!Taskkill /IM '.shellescape('%:r').'.exe /F'<CR>
autocmd filetype autohotkey nnoremap <C-S-F5> :silent exec '!Taskkill /IM '.shellescape('%:r').'.exe /F' <bar> silent exec '!"C:\Program Files\AutoHotkey\Compiler\Ahk2Exe.exe" /in '.shellescape('%').' && start .\'.shellescape('%:r')<CR>

How do I have these exec commands keep the cmd window open only if there is an error?

(e.g. if I run the ctrl+F5 and the compiled version is already running, the compile will fail because it can't write to the .exe. (Yes, I know in that particular case there's an evil modal popup but in other cases, there's not good feedback of failure.))

Answer 1

If the AutoHotkey compiler properly reports its success via the exit status (I haven't checked), you can keep the :silent and just delay the closing of the command prompt by executing the pause command (which waits for a keypress) in case compilation fails:

:silent exec '!"C:\Program Files\AutoHotkey\Compiler\Ahk2Exe.exe" /in '.shellescape('%') . ' || pause'<CR>

and here's a reference for the command failed redirect (double pipe ||)

Alternatives

You could invoke the external command via :let output = system(...), and then conditionally :echo or discard the output based on v:shell_error (or even by inspecting the output by matching "interesting" strings, if you want to ignore some compiler errors or as a solution if the exit status always is 0).

Actually, you then should go the whole round and write a proper compiler plugin (:help :compiler, :help write-compiler-plugin). With this, you can trigger via :make, and can use the quickfix list to view and navigate to compiler errors (assuming the error output is properly structured and parsable).

Additional critique

nnoremap <S-F5> ...

As these mappings only apply to AutoHotkey buffers, you should limit the scope of those mappings via :nnoremap <buffer> ...

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I would recommend putting any settings, mappings, and filetype-specific autocmds into ~/.vim/ftplugin/{filetype}_whatever.vim (or {filetype}/whatever.vim; cp. :help ftplugin-name) instead of defining lots of :autocmd FileType {filetype}; it's cleaner and scales better; requires that you have :filetype plugin on, though. Settings that override stuff in default filetype plugins should go into ~/.vim/after/ftplugin/{filetype}.vim instead.