Recognise ß properly as a lower-case letter (bug#11309)

ß was incorrectly treated as a caseless character and thus not matched
by the regexp [[:lower:]] (or, in case-folding mode, [[:upper:]]).
The reason is that the upcase table maps it to itself, which can be
remedied by mapping it to ẞ (U+7838) instead.  Doing so does not
affect upcasing since the special-uppercase property maps it to SS.

* lisp/international/characters.el (tbl): Map ß to ẞ in the upcase
table.
* test/src/regex-emacs-tests.el (regexp-eszett): Uncomment previously
failing tests.  Add checks to make sure that case transformations
remain valid.

1 files changed, 11 insertions, 4 deletions

diff --git a/test/src/regex-emacs-tests.el b/test/src/regex-emacs-tests.el
index 576630aa5af..34d4067db47 100644
--- a/test/src/regex-emacs-tests.el
+++ b/test/src/regex-emacs-tests.el
@@ -834,6 +834,13 @@ This evaluates the TESTS test cases from glibc."
 
 (ert-deftest regexp-eszett ()
   "Test matching of ß and ẞ."
+  ;; Sanity checks.
+  (should (equal (upcase "ß") "SS"))
+  (should (equal (downcase "ß") "ß"))
+  (should (equal (capitalize "ß") "Ss"))  ; undeutsch...
+  (should (equal (upcase "ẞ") "ẞ"))
+  (should (equal (downcase "ẞ") "ß"))
+  (should (equal (capitalize "ẞ") "ẞ"))
   ;; ß is a lower-case letter (Ll); ẞ is an upper-case letter (Lu).
   (let ((case-fold-search nil))
     (should (equal (string-match "ß" "ß") 0))
@@ -842,8 +849,8 @@ This evaluates the TESTS test cases from glibc."
     (should (equal (string-match "ẞ" "ẞ") 0))
     (should (equal (string-match "[[:alpha:]]" "ß") 0))
     ;; bug#11309
-    ;;(should (equal (string-match "[[:lower:]]" "ß") 0))
-    ;;(should (equal (string-match "[[:upper:]]" "ß") nil))
+    (should (equal (string-match "[[:lower:]]" "ß") 0))
+    (should (equal (string-match "[[:upper:]]" "ß") nil))
     (should (equal (string-match "[[:alpha:]]" "ẞ") 0))
     (should (equal (string-match "[[:lower:]]" "ẞ") nil))
     (should (equal (string-match "[[:upper:]]" "ẞ") 0)))
@@ -854,8 +861,8 @@ This evaluates the TESTS test cases from glibc."
     (should (equal (string-match "ẞ" "ẞ") 0))
     (should (equal (string-match "[[:alpha:]]" "ß") 0))
     ;; bug#11309
-    ;;(should (equal (string-match "[[:lower:]]" "ß") 0))
-    ;;(should (equal (string-match "[[:upper:]]" "ß") 0))
+    (should (equal (string-match "[[:lower:]]" "ß") 0))
+    (should (equal (string-match "[[:upper:]]" "ß") 0))
     (should (equal (string-match "[[:alpha:]]" "ẞ") 0))
     (should (equal (string-match "[[:lower:]]" "ẞ") 0))
     (should (equal (string-match "[[:upper:]]" "ẞ") 0))))