master 25d15391f26 6/7: Normalize ISUPPORT params with empty values in ERC

[F. Jason Park]

branch: master
commit 25d15391f2683ea95c4d7ee291fb82e0c9858d73
Author: F. Jason Park <jp@neverwas.me>
Commit: F. Jason Park <jp@neverwas.me>

    Normalize ISUPPORT params with empty values in ERC
    
    * lisp/erc/erc-backend.el (erc-server-parameters)
    (erc--isupport-params): Mention parsing and storage behavior regarding
    nonstandard "FOO=" tokens.
    (erc--parse-isupport-value): Move comment closer to code.
    (erc--get-isupport-entry): Treat the empty string as truly null, as
    prescribed by the Brocklesby draft cited in the top-level comment.
    * test/lisp/erc/erc-tests.el (erc--get-isupport-entry): Add case for
    the empty string appearing as a value for an `erc-server-parameters'
    item.
    (erc-server-005): Assert compat-related behavior of retaining the
    empty string as a valid value from a raw "FOO=" token.
    (Bug#67220)
---
 lisp/erc/erc-backend.el    | 21 +++++++++++++--------
 test/lisp/erc/erc-tests.el | 26 ++++++++++++++++++--------
 2 files changed, 31 insertions(+), 16 deletions(-)

diff --git a/lisp/erc/erc-backend.el b/lisp/erc/erc-backend.el
index e379066b08e..2aaedad1b64 100644
--- a/lisp/erc/erc-backend.el
+++ b/lisp/erc/erc-backend.el
@@ -254,6 +254,11 @@ Entries are of the form:
 or
   (PARAMETER) if no value is provided.
 
+where PARAMETER is a string and VALUE is a string or nil.  For
+compatibility, a raw parameter of the form \"FOO=\" becomes
+(\"FOO\" . \"\") even though it's equivalent to the preferred
+canonical form \"FOO\" and its lisp representation (\"FOO\").
+
 Some examples of possible parameters sent by servers:
 CHANMODES=b,k,l,imnpst - list of supported channel modes
 CHANNELLEN=50 - maximum length of channel names
@@ -273,7 +278,8 @@ WALLCHOPS - supports sending messages to all operators in a 
channel")
 (defvar-local erc--isupport-params nil
   "Hash map of \"ISUPPORT\" params.
 Keys are symbols.  Values are lists of zero or more strings with hex
-escapes removed.")
+escapes removed.  ERC normalizes incoming parameters of the form
+\"FOO=\" to (FOO).")
 
 ;;; Server and connection state
 
@@ -2150,10 +2156,6 @@ Then display the welcome message."
   ;;
   ;; > The server SHOULD send "X", not "X="; this is the normalized form.
   ;;
-  ;; Note: for now, assume the server will only send non-empty values,
-  ;; possibly with printable ASCII escapes.  Though in practice, the
-  ;; only two escapes we're likely to see are backslash and space,
-  ;; meaning the pattern is too liberal.
   (let (case-fold-search)
     (mapcar
      (lambda (v)
@@ -2164,7 +2166,9 @@ Then display the welcome message."
                      (string-match "[\\]x[0-9A-F][0-9A-F]" v start))
            (setq m (substring v (+ 2 (match-beginning 0)) (match-end 0))
                  c (string-to-number m 16))
-           (if (<= ?\  c ?~)
+           ;; In practice, this range is too liberal.  The only
+           ;; escapes we're likely to see are ?\\, ?=, and ?\s.
+           (if (<= ?\s c ?~)
                (setq v (concat (substring v 0 (match-beginning 0))
                                (string c)
                                (substring v (match-end 0)))
@@ -2189,8 +2193,9 @@ primitive value."
                                           (or erc-server-parameters
                                               (erc-with-server-buffer
                                                 erc-server-parameters)))))
-                       (if (cdr v)
-                           (erc--parse-isupport-value (cdr v))
+                       (if-let ((val (cdr v))
+                                ((not (string-empty-p val))))
+                           (erc--parse-isupport-value val)
                          '--empty--)))))
       (pcase value
         ('--empty-- (unless single (list key)))
diff --git a/test/lisp/erc/erc-tests.el b/test/lisp/erc/erc-tests.el
index dad161a2827..4762be468a5 100644
--- a/test/lisp/erc/erc-tests.el
+++ b/test/lisp/erc/erc-tests.el
@@ -1054,7 +1054,8 @@
 
 (ert-deftest erc--get-isupport-entry ()
   (let ((erc--isupport-params (make-hash-table))
-        (erc-server-parameters '(("FOO" . "1") ("BAR") ("BAZ" . "A,B,C")))
+        (erc-server-parameters '(("FOO" . "1") ("BAR") ("BAZ" . "A,B,C")
+                                 ("SPAM" . "")))
         (items (lambda ()
                  (cl-loop for k being the hash-keys of erc--isupport-params
                           using (hash-values v) collect (cons k v)))))
@@ -1075,7 +1076,9 @@
     (should (equal (erc--get-isupport-entry 'FOO) '(FOO "1")))
 
     (should (equal (funcall items)
-                   '((BAR . --empty--) (BAZ "A" "B" "C") (FOO "1"))))))
+                   '((BAR . --empty--) (BAZ "A" "B" "C") (FOO "1"))))
+    (should (equal (erc--get-isupport-entry 'SPAM) '(SPAM)))
+    (should-not (erc--get-isupport-entry 'SPAM 'single))))
 
 (ert-deftest erc-server-005 ()
   (let* ((hooked 0)
@@ -1093,34 +1096,41 @@
                (lambda (_ _ _ line) (push line calls))))
 
       (ert-info ("Baseline")
-        (setq args '("tester" "BOT=B" "EXCEPTS" "PREFIX=(ov)@+" "are supp...")
+        (setq args '("tester" "BOT=B" "CHANTYPES=" "EXCEPTS" "PREFIX=(ov)@+"
+                     "are supp...")
               parsed (make-erc-response :command-args args :command "005"))
 
         (setq verify
               (lambda ()
                 (should (equal erc-server-parameters
                                '(("PREFIX" . "(ov)@+") ("EXCEPTS")
+                                 ;; Should be ("CHANTYPES") but
+                                 ;; retained for compatibility.
+                                 ("CHANTYPES" . "")
                                  ("BOT" . "B"))))
                 (should (zerop (hash-table-count erc--isupport-params)))
                 (should (equal "(ov)@+" (erc--get-isupport-entry 'PREFIX t)))
                 (should (equal '(EXCEPTS) (erc--get-isupport-entry 'EXCEPTS)))
                 (should (equal "B" (erc--get-isupport-entry 'BOT t)))
-                (should (string= (pop calls)
-                                 "BOT=B EXCEPTS PREFIX=(ov)@+ are supp..."))
+                (should (string=
+                         (pop calls)
+                         "BOT=B CHANTYPES= EXCEPTS PREFIX=(ov)@+ are supp..."))
                 (should (equal args (erc-response.command-args parsed)))))
 
         (erc-call-hooks nil parsed))
 
       (ert-info ("Negated, updated")
-        (setq args '("tester" "-EXCEPTS" "-FAKE" "PREFIX=(ohv)@%+" "are su...")
+        (setq args '("tester" "-EXCEPTS" "-CHANTYPES" "-FAKE" "PREFIX=(ohv)@%+"
+                     "are su...")
               parsed (make-erc-response :command-args args :command "005"))
 
         (setq verify
               (lambda ()
                 (should (equal erc-server-parameters
                                '(("PREFIX" . "(ohv)@%+") ("BOT" . "B"))))
-                (should (string= (pop calls)
-                                 "-EXCEPTS -FAKE PREFIX=(ohv)@%+ are su..."))
+                (should (string-prefix-p
+                         "-EXCEPTS -CHANTYPES -FAKE PREFIX=(ohv)@%+ "
+                         (pop calls)))
                 (should (equal "(ohv)@%+" (erc--get-isupport-entry 'PREFIX t)))
                 (should (equal "B" (erc--get-isupport-entry 'BOT t)))
                 (should-not (erc--get-isupport-entry 'EXCEPTS))