tools: Fix emacs compiler warnings (#4451)

[leoliu]

Do not depend on cl. Assume presence of before-save-hook (Emacs 22)
and remove erlang-check-module-name-init. Remove (run-hooks
'erlang-mode-hook) from erlang-mode definition because
define-derived-mode does it already. Replace erlang-caddr with caddr
from Emacs 26.

erlang.el now compiles cleanly in Emacs 24.5, 25, 26, 27.

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[dgud]

The test case emacs_SUITE:compile_and_load still fails on emacs-27.1, not really your problem but you know much more about
emacs lisp than me, would appreciate if you have the time to take a look.

The same testcase fails on emacs-25.2 which it didn't before:

    space_Ω_/lib/erlang/lib/tools-3.5/emacs/erlang.el:6302:1:Warning: the
    function ‘caddr’ is not known to be defined.
../../../otp/elib with space_Ω_/lib/erlang/lib/tools-3.5/emacs/erlang.el:6302:1:Error: Symbol’s value as variable is void: %s
>>Error occurred processing /ldisk/daily_build/24_master-opu_o_bindir.2021-02-24_21/otp/elib with space_Ω_/lib/erlang/lib/tools-3.5/emacs/erlang.el: Symbol's value as variable is void ((%s))

[leoliu]

I looked at emacs_SUITE.erl and it seems this line might be problematic. Not sure if that's the culprit though.

diff --git a/lib/tools/test/emacs_SUITE.erl b/lib/tools/test/emacs_SUITE.erl
index e5587b35..f74a159c 100644
--- a/lib/tools/test/emacs_SUITE.erl
+++ b/lib/tools/test/emacs_SUITE.erl
@@ -107,7 +107,7 @@ compile_and_load(_Config) ->
                 %% Workaround byte-compile-error-on-warn which seem broken in
                 %% Emacs 25.
                 "\"(advice-add #'display-warning :after "
-                    "(lambda (_ f _ _) (error \"%s\" f)))\"";
+                    "(lambda (_ f &optional _ _) (error \\\"%s\\\" f)))\"";
             _ ->
                 "\"(setq byte-compile-error-on-warn t)\""
         end,

I also found erldoc.el compiles with a warning under emacs 27. Is this what's causing the failure? Though the warning can be suppressed with the following simple change it might be a regression on emacs' side. I will check with emacs upstream to see what's happening to eval-and-compile:

diff --git a/lib/tools/emacs/erldoc.el b/lib/tools/emacs/erldoc.el
index a8ac81ec..5d185e1f 100644
--- a/lib/tools/emacs/erldoc.el
+++ b/lib/tools/emacs/erldoc.el
@@ -62,6 +62,7 @@
 
 (eval-when-compile (require 'url-parse))
 (require 'cl-lib)
+(require 'json)
 (require 'erlang)
 
 (eval-and-compile                       ;for emacs < 24.3
@@ -268,7 +269,6 @@ (defun erldoc-parse-all (man-index output &optional json)
     (with-temp-buffer
       (if (not json)
           (pp table (current-buffer))
-        (eval-and-compile (require 'json))
         (let ((json-encoding-pretty-print t))
           (insert (json-encode table))))
       (unless (file-directory-p (file-name-directory output))

[dgud]

You can run with make test ARGS="-suite emacs_SUITE" from $ERL_TOP/lib/tools

Yes warnings are errors if emacs > 25 and I understand the testcase correct.

And it fails on erldoc:

emacs --batch --quick --directory "/ldisk/daily_build/24_master-opu_o.2021-02-24_21/otp/lib/erlang/lib/tools-3.5/emacs" --eval "(require 'erlang-start)" --eval "(setq byte-compile-error-on-warn t)"  -f batch-byte-compile "/ldisk/daily_build/24_master-opu_o.2021-02-24_21/otp/lib/erlang/lib/tools-3.5/emacs/erldoc.el"

 => 1 Loading erlang-skels...
In toplevel form:
../../../otp/lib/erlang/lib/tools-3.5/emacs/erldoc.el:534:1:Error: the following functions might not be defined at runtime: json-encode, cl-reduce, cl-mapcan

The other modules have warnings as well, but doesn't seem to fail the testcase, I have not had time to dig deeper yet.

[leoliu]

Thanks for the tip make test ARGS="-suite emacs_SUITE". After some trial and error I was able to fix the failed tests and some warnings and errors that I found in the logs.

Somehow (eval-when-compile (require 'url-parse)) has to be moved to after (require 'cl-lib) in erldoc.el to address the following functions might not be defined at runtime: cl-reduce, cl-mapcan.

[dgud]

Thanks.