[elpa] externals/xr d6740ce 2/3: Detect misplaced `]' inside character alternatives

[Mattias Engdegård]

branch: externals/xr
commit d6740ceb190e71bab2d992f2ad35b9f6418283de
Author: Mattias Engdegård <address@hidden>
Commit: Mattias Engdegård <address@hidden>

    Detect misplaced `]' inside character alternatives
    
    Add an ad-hoc check for a rare but serious mistake: attempts to include
    literal [ and ] inside a character alternative without placing the ] first,
    resulting in a [...[...]...] pattern.
    
    There could be false positives but none have been seen in emacs or elpa.
---
 xr-test.el |  4 ++++
 xr.el      | 15 +++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/xr-test.el b/xr-test.el
index 670a2f2..4d197bf 100644
--- a/xr-test.el
+++ b/xr-test.el
@@ -356,6 +356,10 @@
                  '((1 . "Uncounted repetition"))))
   (should (equal (xr-lint "a\\{\\}")
                  '((1 . "Implicit zero repetition"))))
+  (should (equal (xr-lint "[0-9[|]*/]")
+                 '((4 . "Suspect `[' in char alternative"))))
+  (should (equal (xr-lint "[^][-].]")
+                 nil))
   )
 
 (provide 'xr-test)
diff --git a/xr.el b/xr.el
index db0adda..eba3a10 100644
--- a/xr.el
+++ b/xr.el
@@ -126,6 +126,21 @@
        ;; plain character (including ^ or -)
        (t
         (let ((ch (following-char)))
+          (when (and (eq ch ?\[)
+                     ;; Ad-hoc pattern attempting to catch mistakes
+                     ;; on the form [...[...]...]
+                     ;; where we are    ^here
+                     (looking-at (rx "["
+                                     (zero-or-more (not (any "[]")))
+                                     "]"
+                                     (zero-or-more (not (any "[]")))
+                                     (not (any "[\\"))
+                                     "]"))
+                     ;; Only if the alternative didn't start with ]
+                     (not (and intervals
+                               (eq (aref (car (last intervals)) 0) ?\]))))
+            (xr--report warnings (point)
+                        "Suspect `[' in char alternative"))
           (push (vector ch ch (point)) intervals))
         (forward-char 1))))