[elpa] externals/xr 658f469058 3/7: Add check for erroneous escape sequences in character alternatives

[ELPA Syncer]

branch: externals/xr
commit 658f4690584ecda813c2ee5c03c0ba25f9a93a53
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Add check for erroneous escape sequences in character alternatives
    
    This detects patterns like "[ \\t]" and "[\\d.]" that may be a
    mistaken use of escape sequences where none is allowed, or too
    many backslashes. Only enabled for checks = `all`.
---
 README     | 11 +++++++++++
 xr-test.el |  8 ++++++++
 xr.el      | 13 +++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/README b/README
index 314a161ffe..07b3d76516 100644
--- a/README
+++ b/README
@@ -127,6 +127,17 @@ The xr package can be used interactively or by other code 
as a library.
     + and -.
     This check is only enable when CHECKS=all.
 
+  - Possibly erroneous '\X' in character alternative
+
+    A character alternative includes something that looks like a
+    escape sequence, but no escape sequences are allowed there since
+    backslash is not a special character in that context.
+    It could also be a caused by too many backslashes.
+
+    For example, "[\\n\\t]" matches the characters 'n', 't' and
+    backslash, but could be an attempt to match newline and tab.
+    This check is only enable when CHECKS=all.
+
   - Duplicated character class '[:class:]'
 
     A character class occurs twice in a single character alternative
diff --git a/xr-test.el b/xr-test.el
index 7eccd8dd80..4e8d1fadfc 100644
--- a/xr-test.el
+++ b/xr-test.el
@@ -488,6 +488,14 @@
               '((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)
+          (if (eq checks 'all)
+              '((2 . "Possibly erroneous `\\t' in character alternative")
+                (8 . "Possibly erroneous `\\d' in character alternative")
+                (12 . "Possibly erroneous `\\S' in character alternative")))))
         ))))
 
 (ert-deftest xr-lint-repetition-of-empty ()
diff --git a/xr.el b/xr.el
index e8ba75582c..f81a4d9e5e 100644
--- a/xr.el
+++ b/xr.el
@@ -204,6 +204,19 @@
            warnings (point)
            (format-message
             "Literal `-' not first or last in character alternative")))
+        (when (eq checks 'all)
+          (let ((last (car-safe intervals)))
+            (when (and last
+                       (eq (aref last 1) ?\\)
+                       (or (memq ch '( ?t ?n ?r ?f ?x ?e ?b  ; char escapes
+                                       ?s ?S ?d ?D ?w ?W))   ; PCRE sequences
+                           (and (<= ?0 ch ?7)))              ; octal escapes
+                       ;; Suppress some common false positives, eg [\\nrt]
+                       (not (looking-at-p (rx (= 2 (in "tnrfeb"))))))
+              (xr--report
+               warnings (- (point) 1)
+               (format-message
+                "Possibly erroneous `\\%c' in character alternative" ch)))))
         (push (vector ch ch (point)) intervals)
         (forward-char))))