[elpa] externals/xr 054824b57b 4/7: Add check for \(:? as a typo for \(?: (#6)

[ELPA Syncer]

branch: externals/xr
commit 054824b57b6adc058ea966b8fa5364a9c461ab43
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Add check for \(:? as a typo for \(?: (#6)
    
    Only enabled for checks = `all`.
    Suggested by Basil Contovounesios.
---
 README     | 6 ++++++
 xr-test.el | 5 ++++-
 xr.el      | 9 +++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/README b/README
index 07b3d76516..fe9ae7cc11 100644
--- a/README
+++ b/README
@@ -247,6 +247,12 @@ The xr package can be used interactively or by other code 
as a library.
     In general, A?, where A matches the empty string, can be
     simplified to just A.
 
+  - Possibly mistyped ':?' at start of group
+
+    A group starts as \(:? which makes it likely that it was really
+    meant to be \(?: -- ie, a non-capturing group.
+    This check is only enable when CHECKS=all.
+
   - Unnecessarily escaped 'X'
 
     A character is backslash-escaped in a skip set despite not being
diff --git a/xr-test.el b/xr-test.el
index 4e8d1fadfc..4166766dc2 100644
--- a/xr-test.el
+++ b/xr-test.el
@@ -488,7 +488,6 @@
               '((4 . "Suspect character range `+-/': should `-' be literal?")
                 (10 . "Suspect character range `&-+': should `-' be literal?"))
             nil)))
-
         (should
          (equal
           (xr-lint "[ \\t][-.\\d][\\Sw][\\rnt]" nil checks)
@@ -496,6 +495,10 @@
               '((2 . "Possibly erroneous `\\t' in character alternative")
                 (8 . "Possibly erroneous `\\d' in character alternative")
                 (12 . "Possibly erroneous `\\S' in character alternative")))))
+        (should (equal (xr-lint "\\(?:ta\\)\\(:?da\\)\\(:?\\)" nil checks)
+                       (if (eq checks 'all)
+                           '((10 . "Possibly mistyped `:?' at start of group"))
+                         nil)))
         ))))
 
 (ert-deftest xr-lint-repetition-of-empty ()
diff --git a/xr.el b/xr.el
index f81a4d9e5e..14231ea796 100644
--- a/xr.el
+++ b/xr.el
@@ -686,6 +686,15 @@ like (* (* X) ... (* X))."
                             (goto-char (match-end 0))
                             (string-to-number (match-string 1)))
                            (t (error "Invalid \\(? syntax"))))
+                      (when (and (eq checks 'all)
+                                 (eq (following-char) ?:)
+                                 (eq (char-after (1+ (point))) ??)
+                                 ;; suppress if the group ends after the :?
+                                 (not (looking-at-p (rx ":?\\)"))))
+                        (xr--report
+                         warnings (point)
+                         (format-message
+                          "Possibly mistyped `:?' at start of group")))
                       'unnumbered))
                    (group (xr--parse-alt warnings purpose checks))
                    ;; simplify - group has an implicit seq