bug#62762: circular dependencies in elisp files and make

[Max Nikulin <manikulin@gmail.com>]

On 13/05/2023 15:46, Eli Zaretskii wrote:
>> Date: Sat, 13 May 2023 14:34:06 +0700 From: Max Nikulin
>>
>> 1. A script reads dependency files (if they exist) created during
>> previous build and removes stale .elc files.
> 
> This will break if the updated files have different dependencies.  You
> need to recreate the dependencies each build.

Let's consider a.el that contains (require 'd) or it autoloads some 
macro from d.el. If a.el changed then a.elc is removed on this stage, so 
updated a.elc will be created on the next stage. Dependency on d.elc is 
known from previous build, so if d.el is changed then both a.elc and 
d.elc are removed. If new (require 'd-new) is added to a.el then it is 
not a problem as well. a.elc is removed due to changed a.el. d-new.elc 
is either up to date or it is removed due to changes in its dependencies 
or in d-new.el.

So no stale files should survive stage 1. The only issue with obsolete 
dependencies is that compilation order may be not optimal.

> Also, it is not clear what is the plan for the macros.  If one of the
> macros used during byte compilation changes in incompatible ways,
> trying to byte-compile using Emacs which preloaded the previous
> (outdated) definition of the macro will fail.

I hope, it is addressed above.

>  So some changes need
> also to generate a new Emacs binary, not just byte-compile in the
> right order.

I expect that dependencies of the script removing stale files are 
minimized. If changes in the breaks this script then it is time for 
"make clean". If emacs binary depends on .elc files then some file may 
be touched to let "make" know that the executable needs rebuild.

>> 2. Normal "make" pass that takes into account dependency between files
>> for ordering of compile commands. Dependency files are created or
>> updated as a side-effect of compilation.
>>
>> Likely it is reasonable to split stage 2 into steps similar to current
>> targets like main-first and mark most of files as dependent on a target
>> that (throw its dependencies) compiles files required for byte compilation.
> 
> What is the plan for the various autoloads files?  They depend on all
> the files, and many (all?) files depend on them.

My plan is that autoloads/loaddefs are order-only dependencies for .elc 
files. However autoloads/loaddefs files depends on all files necessary 
to generate them.