Subject: bug#31688: 26.1.50; Byte compiler confuses two string variables

From: Gemini Lasswell <[email-masked]>
Date: Sat, 02 Jun 2018 10:51:18 -0700

Here is a test which succeeds when interpreted and fails when
byte-compiled. The byte compiler is apparently confusing two string
variables, or optimizing away one of them.  I've tried it both
with and without lexical-binding with the same results.

To reproduce, save this to bug.el:

(require 'ert)
(ert-deftest test-strings-props ()
  (let* ((str1 "abcdefghij")
         (obj '(a b))
         (str2 "abcdefghij"))
    (put-text-property 0 5 'test obj str2)
    (should (equal "\"abcdefghij\"" (prin1-to-string str1)))))

Then:
C-u M-x byte-compile-file RET bug.el RET
M-x ert RET t RET

Result:

    (ert-test-failed
     ((should
       (equal "\"abcdefghij\""
	      (prin1-to-string str1)))
      :form
      (equal "\"abcdefghij\"" "#(\"abcdefghij\" 0 5 (test (a b)))")
      :value nil :explanation
      (arrays-of-different-length 12 32 "\"abcdefghij\"" "#(\"abcdefghij\" 0 5 (test (a b)))" first-mismatch-at 0)))