Fontify python escape sequences in literals

* lisp/progmodes/python.el (python-rx): Add regular expressions
matching escape codes in string and byte literals
(python--string-bytes-literal-matcher): new function
(python--not-raw-bytes-literal-start-regexp): new constant
(python--not-raw-string-literal-start-regexp): new constant
* test/lisp/progmodes/python-tests.el: Add tests for new
fontification (bug#57004).

1 files changed, 54 insertions, 2 deletions

diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index b8fc7d4c546..27bdbae3113 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -427,7 +427,19 @@ This variant of `rx' supports common Python named REGEXPS."
                                  (: "vim:" (* space) "set" (+ space)
                                     "fileencoding" (* space) ?= (* space)
                                     (group-n 1 (+ (or word ?-)))
-                                    (* space) ":")))))
+                                    (* space) ":"))))
+            (bytes-escape-sequence
+             (seq (not "\\")
+                  (group (or "\\\\" "\\'" "\\a" "\\b" "\\f"
+                             "\\n" "\\r" "\\t" "\\v"
+                             (seq "\\" (= 3 (in "0-7")))
+                             (seq "\\x" hex hex)))))
+            (string-escape-sequence
+             (or bytes-escape-sequence
+                 (seq (not "\\")
+                      (or (group-n 1 "\\u" (= 4 hex))
+                          (group-n 1 "\\U" (= 8 hex))
+                          (group-n 1 "\\N{" (*? anychar) "}"))))))
      (rx ,@regexps)))
 
 
@@ -539,6 +551,29 @@ the {...} holes that appear within f-strings."
         (goto-char (min limit (1+ send)))
         (setq ppss (syntax-ppss))))))
 
+(defconst python--not-raw-bytes-literal-start-regexp
+  (rx (or bos (not alnum)) (or "b" "B") (or "\"" "\"\"\"" "'" "'''") eos)
+  "A regular expression matching the start of a not-raw bytes literal.")
+
+(defconst python--not-raw-string-literal-start-regexp
+  (rx (or bos (not alnum)) (? (or "u" "U" "F" "f")) (or "\"" "\"\"\"" "'" "'''") eos)
+  "A regular expression matching the start of a not-raw string literal.")
+
+(defun python--string-bytes-literal-matcher (regexp start-regexp)
+  "Match REGEXP within a string or bytes literal whose start matches START-REGEXP."
+  (lambda (limit)
+    (cl-loop for result = (re-search-forward regexp limit t)
+             for result-valid = (and
+                                 result
+                                 (let* ((pos (nth 8 (syntax-ppss)))
+                                        (before-quote
+                                         (buffer-substring-no-properties
+                                          (max (- pos 5) (point-min))
+                                          (min (+ pos 1) (point-max)))))
+                                   (string-match-p start-regexp before-quote)))
+             until (or (not result) result-valid)
+             finally return (and result-valid result))))
+
 (defvar python-font-lock-keywords-level-1
   `((,(python-rx symbol-start "def" (1+ space) (group symbol-name))
      (1 font-lock-function-name-face))
@@ -716,7 +751,24 @@ sign in chained assignment."
                   grouped-assignment-target (* space)
                   (or ")" "]") (* space)
                   assignment-operator))
-     (1 font-lock-variable-name-face)))
+     (1 font-lock-variable-name-face))
+    ;; escape sequences within bytes literals
+    ;;   "\\" "\'" "\a" "\b" "\f" "\n" "\r" "\t" "\v"
+    ;;   "\ooo" character with octal value ooo
+    ;;   "\xhh" character with hex value hh
+    (,(python--string-bytes-literal-matcher
+       (python-rx bytes-escape-sequence)
+       python--not-raw-bytes-literal-start-regexp)
+     (1 font-lock-constant-face t))
+    ;; escape sequences within string literals, the same as appear in bytes
+    ;; literals in addition to:
+    ;;   "\uxxxx" Character with 16-bit hex value xxxx
+    ;;   "\Uxxxxxxxx" Character with 32-bit hex value xxxxxxxx
+    ;;   "\N{name}" Character named name in the Unicode database
+    (,(python--string-bytes-literal-matcher
+       (python-rx string-escape-sequence)
+       python--not-raw-string-literal-start-regexp)
+     (1 'font-lock-constant-face t)))
   "Font lock keywords to use in `python-mode' for maximum decoration.
 
 This decoration level includes everything in