[PATCH] csv-mode.el: Add function for reading a CSV line

[Joost Kremers <joostkremers@fastmail.fm>]

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Hi,

@Philip Kaludercic, as per your suggestion
(https://lists.gnu.org/archive/html/emacs-devel/2024-05/msg00966.html), here's a
patch for csv-mode.el to add a function for reading a CSV line and unquoting the
resulting field values.

I've put the unquoting in a separate (internal) function, csv--unquote-value,
which also un-escapes escaped quote characters inside the field value. As per
RFC 4180, the escape character is the quote character. The RFC only mentions the
double quotation mark as quote character, but csv-mode.el makes it possible to
use other quote characters, so the patch supports that as well.

I've also added a test for csv--unquote-value.



-- 
Joost Kremers
Life has its moments


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From e97b8b8cca3f987cbdf5e29ec184f37825755eba Mon Sep 17 00:00:00 2001
From: Joost Kremers <joostkremers@fastmail.com>
Date: Wed, 22 May 2024 00:07:34 +0200
Subject: [PATCH] Add function for reading a CSV line and return its values as
 a list.

* (csv-parse-current-row): New function; unlike csv--collect-fields,
  unquotes the field values.
* (csv--unquote-value): New function.
---
 csv-mode-tests.el | 12 ++++++++++++
 csv-mode.el       | 26 +++++++++++++++++++++++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/csv-mode-tests.el b/csv-mode-tests.el
index 0caeab7..ea955a9 100644
--- a/csv-mode-tests.el
+++ b/csv-mode-tests.el
@@ -144,5 +144,17 @@
              (csv--separator-score ?\; csv-tests--data
                                    (length csv-tests--data)))))
 
+(ert-deftest csv-tests-unquote-value ()
+  (should (equal (csv--unquote-value "Hello, World")
+                 "Hello, World"))
+  (should (equal (csv--unquote-value "\"Hello, World\"")
+                 "Hello, World"))
+  (should (equal (csv--unquote-value "Hello, \"\"World")
+                 "Hello, \"\"World"))
+  (should (equal (csv--unquote-value "\"Hello, \"\"World\"\"\"")
+                 "Hello, \"World\""))
+  (should (equal (csv--unquote-value "\"Hello, World'")
+                 "\"Hello, World'")))
+
 (provide 'csv-mode-tests)
 ;;; csv-mode-tests.el ends here
diff --git a/csv-mode.el b/csv-mode.el
index f639dcf..09402c2 100644
--- a/csv-mode.el
+++ b/csv-mode.el
@@ -4,7 +4,7 @@
 
 ;; Author: "Francis J. Wright" <F.J.Wright@qmul.ac.uk>
 ;; Maintainer: emacs-devel@gnu.org
-;; Version: 1.23
+;; Version: 1.24
 ;; Package-Requires: ((emacs "27.1") (cl-lib "0.5"))
 ;; Keywords: convenience
 
@@ -107,6 +107,10 @@
 
 ;;; News:
 
+;; Since 1.24
+;; - New function `csv--unquote-value'.
+;; - New function `csv-parse-current-row'.
+
 ;; Since 1.21:
 ;; - New command `csv-insert-column'.
 ;; - New config var `csv-align-min-width' for `csv-align-mode'.
@@ -1400,6 +1404,26 @@ point is assumed to be at the beginning of the line."
 	      (forward-char)))
 	(nreverse fields)))))
 
+(defun csv--unquote-value (value)
+  "Remove quotes around VALUE.
+If VALUE contains escaped quote characters, un-escape them.  If
+VALUE is not quoted, return it unchanged."
+  (save-match-data
+    (let ((quote-regexp (apply #'concat `("[" ,@csv-field-quotes "]"))))
+      (string-match (concat "^\\(" quote-regexp "\\)\\(.*\\)\\(" quote-regexp "\\)$") value)
+      (if-let ((quote-char (match-string 1 value))
+               ((equal quote-char (match-string 3 value)))
+               (unquoted (match-string 2 value)))
+          (replace-regexp-in-string (concat quote-char quote-char) quote-char unquoted)
+        value))))
+
+(defun csv-parse-current-row ()
+  "Parse the current CSV line.
+Return the field values as a list."
+  (save-mark-and-excursion
+    (goto-char (line-beginning-position))
+    (mapcar #'csv--unquote-value (csv--collect-fields (line-end-position)))))
+
 (defvar-local csv--header-line nil)
 (defvar-local csv--header-hscroll nil)
 (defvar-local csv--header-string nil)
-- 
2.45.1