[elpa] externals/xr db5f17b 1/3: Check suspicious curly-bracket constructs

[Mattias Engdegård]

branch: externals/xr
commit db5f17b29c96c9a1cfa50cbf831dec1d27cc9e80
Author: Mattias Engdegård <address@hidden>
Commit: Mattias Engdegård <address@hidden>

    Check suspicious curly-bracket constructs
    
    Warn about \{\} and \{,\} (which really mean \{0\} and *),
    and signal an error for \{N,M\} where N>M.
---
 xr-test.el | 5 +++++
 xr.el      | 7 +++++++
 2 files changed, 12 insertions(+)

diff --git a/xr-test.el b/xr-test.el
index c1c9b31..670a2f2 100644
--- a/xr-test.el
+++ b/xr-test.el
@@ -56,6 +56,7 @@
                  '(repeat 0 1 "a")))
   (should (equal (xr "a\\{1,\\}")
                  '(>= 1 "a")))
+  (should-error (xr "a\\{3,2\\}"))
   )
 
 (ert-deftest xr-backref ()
@@ -351,6 +352,10 @@
                  '((22 . "Duplicated character class `[:digit:]'"))))
   (should (equal (xr-lint "a*\\|b+\\|\\(?:a\\)*")
                  '((8 . "Duplicated alternative branch"))))
+  (should (equal (xr-lint "a\\{,\\}")
+                 '((1 . "Uncounted repetition"))))
+  (should (equal (xr-lint "a\\{\\}")
+                 '((1 . "Implicit zero repetition"))))
   )
 
 (provide 'xr-test)
diff --git a/xr.el b/xr.el
index 24249aa..db0adda 100644
--- a/xr.el
+++ b/xr.el
@@ -342,6 +342,8 @@
 ;; Apply a repetition of {LOWER,UPPER} to OPERAND.
 ;; UPPER may be nil, meaning infinity.
 (defun xr--repeat (lower upper operand)
+  (when (and upper (> lower upper))
+    (error "Invalid repetition interval"))
   ;; rx does not accept (= 0 ...) or (>= 0 ...), so we use 
   ;; (repeat 0 0 ...) and (zero-or-more ...), respectively.
   ;; Note that we cannot just delete the operand if LOWER=UPPER=0,
@@ -420,6 +422,11 @@
                   (comma (match-string 2))
                   (upper (and (match-string 3)
                               (string-to-number (match-string 3)))))
+              (unless (or (match-beginning 1) (match-string 3))
+                (xr--report warnings (- (match-beginning 0) 2)
+                            (if comma
+                                "Uncounted repetition"
+                                "Implicit zero repetition")))
               (goto-char (match-end 0))
               (setq sequence (cons (xr--repeat
                                     lower