RFC: Image dumping and program-op

[Elias Pipping]

Dear list,

from within a REPL, oftentimes, you can save the current status and create a file that’ll allow you to continue where you are now at a later point in time. This file could be a standalone executable or a core file that requires a lisp environment to run (e.g. via `lisp -core …`).
These two cases can be subdivided into four overall use cases.

(exe-repl) When the executable is run, you want it to print a banner and take you to a REPL. Maybe you’ve created this file after applying a patch to your lisp and you don’t want to do that over and over again.
(exe-application) You’ve created an executable that should not print a banner and run an entirely new main() function.

(core-repl) Analogous to the exe-repl case, but smaller at the cost of requiring a lisp to run
(core-application) Analogous to the exe-application case (not sure if anyone does this).

The function `uiop:dump-image` can be used to create images, where ‘image’ is an umbrella term for both standalone executables and cores. With :executable t, it creates the former; with :executable nil, the latter. The image is only told whether we want a REPL or application type image once it’s run and uiop:restore-image hands control over to what uiop:*image-entry-point*.

That seems to work for some lisps, but for CMU CL it does not. CMU CL’s save-image provides options like

 :process-command-line t/nil
 :print-herald t/nil

Whether the herald/banner is printed on startup is decided when save-image is called. It cannot be changed later. If you’re writing an application with a main method, and you don’t pass :print-herald nil, the banner will be printed before your application does anything else. If you want to read a list of options and arguments from the command line in your main method, this will not work if you passed :process-command-line nil to save-image, since then the command line arguments will be frozen (i.e., equal what they were when you called save-image).

This suggests that for uiop:dump-image to cover relevant use cases on CMU CL, it will have to learn about the repl/application distinction, e.g. by growing another option.

I’ve created a sample application that illustrates this and put it here(*):

 https://github.com/pipping/cl-echo

echo.lisp does what its name suggests: It tells you what it is that you passed to it. If I want to create an exe-application type image from it, on sbcl e.g. that’ll work with uiop:dump-image and I can even use asdf’s program-op (please see build.lisp for how)

For CMU CL, (uiop:dump-image :executable t) and asdf's program-op do something that I do not want: They leave the command line arguments frozen so that the resulting executable does not return what I want it to. I need something that’s different from what asdf’s program-op in build.lisp does (in particular, not pass :process-command-line nil), as is shown in build-cmucl.lisp.

Were I to pass :print-herald nil with :executable t in uiop:dump-image on CMU CL, I’d make the exe-application case work as expected but not the exe-repl case. Hence my claim that we need a new option.

If we add another option to dump-image, the question is how asdf's image-op and program-op should behave (here, the word image refers to core files only, as far as I can tell). Will we need new options here, too? If so, what should the defaults be?

This write-up is the result of a conversation with Robert. Thanks again, Robert!

I’d welcome feedback.


Elias

(*) The current version at the time of this writing is 

 https://github.com/pipping/cl-echo/tree/faea91b6aa14ea81f2130edef3f6abccbd5fa176

so if my notes don’t seem to make any sense, please give that revision a try.