bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Package: Emacs
Version: 29.0.50


As the title says, if you enable `flymake-mode` in an ELisp file with
a `no-byte-compile: t` in its file-local variables you don't get any
diagnostics from the compiler (you do still get diagnostics from
checkdoc, admittedly).

I think `no-byte-compile` only means that we should load the `.el` file
and not generate a `.elc` file and it shouldn't mean that we should
refrain from asking the byte-compiler what is its opinion about the
quality of this code.


        Stefan



In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 1.16.0, Xaw3d scroll bars)
 of 2022-05-27 built on pastel
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bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Lars Ingebrigtsen]

Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs@gnu.org> writes:

> I think `no-byte-compile` only means that we should load the `.el` file
> and not generate a `.elc` file and it shouldn't mean that we should
> refrain from asking the byte-compiler what is its opinion about the
> quality of this code.

I stumbled onto a related thing earlier tonight -- I said `M-x
byte-compile-file RET RET' and then it did nothing -- because of the
no-byte-compile.

I'm not sure whether I agree with that -- if I've explicitly asked Emacs
to do it, I think that should override the cookie.  Or at least issue a
message of some sort.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> I stumbled onto a related thing earlier tonight -- I said `M-x
> byte-compile-file RET RET' and then it did nothing -- because of the
> no-byte-compile.
>
> I'm not sure whether I agree with that -- if I've explicitly asked Emacs
> to do it, I think that should override the cookie.  Or at least issue a
> message of some sort.

That's a slightly different case from mine: the `no-byte-compile` is
often used either because the user really only ever wants to load the
`.el` or because the compilation is known to fail (e.g. because it
requires macros defined in a package that's not marked as a strict
dependency, very common in tests).

Generating a `.elc` file explicitly with `M-x byte-compile-file` could
be a problem if subsequent "normal" use will fail to update that `.elc`
because of the `no-byte-compile`.

So, I think `byte-compile-file` should not silently override the
`no-byte-compile`.  It could prompt to choose between "really compile"
and "compile but don't generate the .elc file".


        Stefan

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Lars Ingebrigtsen]

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

> So, I think `byte-compile-file` should not silently override the
> `no-byte-compile`.  It could prompt to choose between "really compile"
> and "compile but don't generate the .elc file".

Yup.  Or perhaps just issue a message that it's not doing anything --
this is a pretty obscure situation, after all.

By the way, do we have a convenient command for "compile but don't
generate the .elc file" somewhere?  (I feel like I've asked this before,
but I've suppressed the memory of the answer.)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[João Távora]

Hi Stefan,

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

> That's a slightly different case from mine: the `no-byte-compile` is
> often used either because the user really only ever wants to load the
> `.el` or because the compilation is known to fail (e.g. because it
> requires macros defined in a package that's not marked as a strict
> dependency, very common in tests).

By this you mean that the provider of such macros is not `require`d?
Then I don't understand what Flymake's byte-compilation backend could do
about this either...  As far as I understand it would just red-underline
all the unknown macro-using forms, their bodies wouldn't be checked.  Is
this what you want?  To check the rest of the file regardless?

Of course you know this -- but just to clarify -- the byte-compilation
backend works by launching a Emacs -Q which is asked to byte-compile
only a file containing the current buffer's contents.  During that
byte-compilation nothing more is loaded apart from what is preloaded or
explicitly loaded by the file at compile-time (via require or
eval-when/and-compile stuff).

A related issue is that when there _is_ an explicit require, then the
load-path support is pretty poor: only the current directory is added to
it.  If the `require`'d file lives somewhere else, there's no way to
hint that to the byte-comp backend, with a particular load-path.

Anyway, maybe you could give small example of such a file containing
such a cookie where you think Flymake's "I refuse to lint this" behavior
could be improved.

João

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> Of course you know this -- but just to clarify -- the byte-compilation
> backend works by launching a Emacs -Q which is asked to byte-compile
> only a file containing the current buffer's contents.  During that
> byte-compilation nothing more is loaded apart from what is preloaded or
> explicitly loaded by the file at compile-time (via require or
> eval-when/and-compile stuff).

This bug-report is about the fact that there is no benefit to
obeying `no-byte-compile` in flymake.  Not about improving the way the
sub-process reproduces a "good" initial state to compile the file
(e.g. set up of `load-path` and whatnot).

> Anyway, maybe you could give small example of such a file containing
> such a cookie where you think Flymake's "I refuse to lint this" behavior
> could be improved.

A good example are all the files in the
[EEV](http://elpa.gnu.org/packages/eev.html) package.


        Stefan

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Lars Ingebrigtsen]

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

> This bug-report is about the fact that there is no benefit to
> obeying `no-byte-compile` in flymake.

Well, there are some.  If you open, say, lisp/net/tramp-loaddefs.el,
you'll get a whole bunch of compilation errors, and you don't want to
see those, I think?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[João Távora]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
>> This bug-report is about the fact that there is no benefit to
>> obeying `no-byte-compile` in flymake.
>
> Well, there are some.  If you open, say, lisp/net/tramp-loaddefs.el,
> you'll get a whole bunch of compilation errors, and you don't want to
> see those, I think?

They could be useful I guess.  There are two cases to distinguish here
(which is what I failed to clarify before).  Perhaps Stefan is thinking
of the second.

1. The file has this form:

      (require 'foo)
       
      (fooey-macro (some-shady-stuff-the-byte-comp-could-look-into))

      (some-more-shady-stuff)

      ;; Local Variables:
      ;; no-byte-compile: t
      ;; End:

   and the reason for adding the no-byte-compile cookie is that foo.el
   can't be found at compile-time.  Then I think there is little reason
   to activate Flymake there.  That's because Flymake will halt at the
   (require 'foo) and not look into the rest of the file.

2. The file is identical but doesn't have the (require 'foo), then, I
   think Flymake will underline the first form, but carry on looking
   into other stuff.  This is possibly helpful, according to one's
   own tolerance of signal-to-noise ratio.

If some files in case 2 are still unbearably noisy for some, then I
think there are existing ways to force Flymake off using buffer-local
variables.
   
João

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> 1. The file has this form:
>
>       (require 'foo)
>        
>       (fooey-macro (some-shady-stuff-the-byte-comp-could-look-into))
>
>       (some-more-shady-stuff)
>
>       ;; Local Variables:
>       ;; no-byte-compile: t
>       ;; End:
>
>    and the reason for adding the no-byte-compile cookie is that foo.el
>    can't be found at compile-time.  Then I think there is little reason
>    to activate Flymake there.  That's because Flymake will halt at the
>    (require 'foo) and not look into the rest of the file.

BTW, while there is little benefit to having flymake run the
byte-compiler here, there is similarly little harm.
And the user may then decide to install `foo` to get the rest of the
file properly checked.


        Stefan

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Lars Ingebrigtsen [2022-06-07 13:54:52] wrote:
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>> This bug-report is about the fact that there is no benefit to
>> obeying `no-byte-compile` in flymake.
> Well, there are some.  If you open, say, lisp/net/tramp-loaddefs.el,
> you'll get a whole bunch of compilation errors, and you don't want to
> see those, I think?

Why not?


        Stefan

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Lars Ingebrigtsen]

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

>> Well, there are some.  If you open, say, lisp/net/tramp-loaddefs.el,
>> you'll get a whole bunch of compilation errors, and you don't want to
>> see those, I think?
>
> Why not?

Because they can't be byte-compiled -- that's why they're marked as
such.  :-/

(There's a separate bug report about that somewhere.)

So we're really using no-byte-compile for two reasons: 1) To say that we
don't think it's useful to byte-compile something or 2) because we know
that it's impossible.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Lars Ingebrigtsen [2022-06-07 14:42:29] wrote:
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>> Well, there are some.  If you open, say, lisp/net/tramp-loaddefs.el,
>>> you'll get a whole bunch of compilation errors, and you don't want to
>>> see those, I think?
>>
>> Why not?
>
> Because they can't be byte-compiled -- that's why they're marked as
> such.  :-/

I don't see the relevance.  I'm not trying to byte-compile the file.
Instead I'm trying to get the byte-compiler to give me feedback about
the file.

Sometimes files marked with `no-byte-compile` will indeed give fairly
poor feedback, but not always, and in any case I find poor feedback
better than no feedback at all.


        Stefan

bug#55811: 29.0.50; No flymake diagnostics for no-byte-compile files

[João Távora]

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

>> Of course you know this -- but just to clarify -- the byte-compilation
>> backend works by launching a Emacs -Q which is asked to byte-compile
>> only a file containing the current buffer's contents.  During that
>> byte-compilation nothing more is loaded apart from what is preloaded or
>> explicitly loaded by the file at compile-time (via require or
>> eval-when/and-compile stuff).
>
> This bug-report is about the fact that there is no benefit to
> obeying `no-byte-compile` in flymake.  Not about improving the way the
> sub-process reproduces a "good" initial state to compile the file
> (e.g. set up of `load-path` and whatnot).

Sure, I understood.  I was just commenting on the fact that the quality
of Flymake diagnostics might not be so good/helpful since those
diagnostics are likely affected by the same root causes that prevent
normal byte compilation anyway.

( Also, on the tangent note about load-path and Flymake, I completely
forgot that I added elisp-flymake-byte-compile-load-path some 4 years
ago.)

>> Anyway, maybe you could give small example of such a file containing
>> such a cookie where you think Flymake's "I refuse to lint this" behavior
>> could be improved.
>
> A good example are all the files in the
> [EEV](http://elpa.gnu.org/packages/eev.html) package.

OK.  Try this "100% untested patch" (TM) then:

diff --git a/lisp/progmodes/elisp-mode.el b/lisp/progmodes/elisp-mode.el
index 70826b4c3a..b99007c938 100644
--- a/lisp/progmodes/elisp-mode.el
+++ b/lisp/progmodes/elisp-mode.el
@@ -2152,7 +2152,9 @@ elisp-flymake--batch-compile-for-flymake
                   collected)
             t)))
     (unwind-protect
-        (byte-compile-file file)
+        (progn
+          (setq-local no-byte-compile nil)
+          (byte-compile-file file))
       (ignore-errors
         (kill-buffer byte-compile-log-buffer)))
     (prin1 :elisp-flymake-output-start)