[PATCH 2/3] test: Deal with Emacs 27 switching to lexical scope by default

[Jonas Bernoulli <jonas@bernoul.li>]

Starting with Emacs 27 undeclared variables in evaluated interactive
code uses lexical scope.  This includes code passed with '--eval' as
we do in the Emacs tests, which also happen to assume dynamic scope.

This can affect variables defined by libraries that we use.  We let-
bind such variables to change the behavior of functions which we then
call with these bindings in effect.  If these libraries are not loaded
beforehand, then the bindings are lexical and fail to have the effect
we intended.

At this time only 'smtpmail' has to be loaded explicitly (for the
variables let-bound in emacs_deliver_message and emacs_fcc_message).

'message' doesn't have to be loaded explicitly, because loading
'notmuch' (in 'run_emacs') already takes care of that, indirectly.

Our own testing-only variables also have to be declared explicitly.
We should have done that anyway, but because of how and where these
variables are used it was very easy to overlook that (i.e. it isn't
something the byte-compiler ever looks at).  Not so in Emacs 27
anymore; here this oversight caused four tests to fail.
---
 test/test-lib.el | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/test/test-lib.el b/test/test-lib.el
index b47b388e..579a20d5 100644
--- a/test/test-lib.el
+++ b/test/test-lib.el
@@ -22,6 +22,12 @@
 
 (require 'cl-lib)
 
+;; Ensure that the dynamic variables that are defined by this library
+;; are defined by the time that we let-bind them.  This is needed
+;; because starting with Emacs 27 undeclared variables in evaluated
+;; interactive code (such as our tests) use lexical scope.
+(require 'smtpmail)
+
 ;; `read-file-name' by default uses `completing-read' function to read
 ;; user input.  It does not respect `standard-input' variable which we
 ;; use in tests to provide user input.  So replace it with a plain
@@ -113,6 +119,9 @@ (defun add-hook-counter (hook)
 (add-hook-counter 'notmuch-hello-mode-hook)
 (add-hook-counter 'notmuch-hello-refresh-hook)
 
+(defvar notmuch-hello-mode-hook-counter -100)
+(defvar notmuch-hello-refresh-hook-counter -100)
+
 (defadvice notmuch-search-process-filter (around pessimal activate disable)
   "Feed notmuch-search-process-filter one character at a time."
   (let ((string (ad-get-arg 1)))
-- 
2.26.0