bug#48079: Temporary files while building after native-comp merge

[Andrea Corallo <akrl@sdf.org>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> Andrea Corallo [2022-01-06 16:10:37] wrote:
>> Eli Zaretskii <eliz@gnu.org> writes:
>>>> In the plain old byte-compiler, these files are *very* short lived
>>>> because they're not created during the compilation itself but only at
>>>> the very end when we save the result to a file (and we just do it by
>>>> first saving to `foo.elcNNMMPP` and then renaming that to `foo.elc`).
>>>> 
>>>> Now with `batch-byte-native-compile-for-bootstrap` apparently we "suspend
>>>> the byte-compiler" right in the middle of this small time window, i.e. after
>>>> writing to `foo.elcNNMMPP` but before its renamed.  Then we call the
>>>> native compiler and only once the native compiler is done, we resume the
>>>> byte compilation which just renames the file and exits.
>>>> 
>>>> If that understanding is correct, then I think we may be able to fix the
>>>> problem by just changing the moment at which we suspend the byte-compiler:
>>>> suspend it *before* it writes to `foo.elcNNMMPP`.
>>>
>>> Are you sure your description above is accurate?
>
> No, but I haven't heard any indication to the contrary either.
>
>>> We have a backtrace in bug#48978 that shows when we create the
>>> .elcXXX temporary file.  My reading of that backtrace is that it's
>>> the other way around: native-compilation invokes byte-compile-file,
>>> which compiles the Lisp into bytecode, creates the file with
>>> make-temp-file, and writes out the bytecode.  It is true that we then
>>> defer renaming of the temporary file in this case
>
> I don't see why you say "the other way around".  Maybe you're putting
> more emphasis on some detail of what I wrote than what I intended.
> The core os what I wrote is that we should change the code so that the
> native compilation takes place before the `.elcNNMMPP` file is written
> rather than after.
>
> AFAICT the native compiler does not read/need that file because it gets
> the same information in a more convenient format straight from
> `bytecomp.el`.
>
>> That's correct,
>
> I don't know what "That" refers to.

Eli's description of how it works.

BR

  Andrea