bug#25534: 26.0; xref ERT tests fail when the source path is mixed case

[Glenn Morris]

Version: 26.2

In an effort to reduce the number of distropatches in Debian, specifically

https://sources.debian.org/patches/emacs/1:26.1+1-1/0008-Don-t-downcase-real-xref-in-elisp-mode-tests.patch/

I have applied the following:

commit 4c6c327
Date:   Tue Dec 18 21:18:31 2018 -0500

    Restrict downcasing in elisp xref tests (bug#25534)
    
    The tests happen to not fail at the moment because find-library-name
    now has an extra feature, find-library--from-load-history, which
    happens to do a case-insensitive regexp match; but still it seems
    better not to rely on this.
    
    * test/lisp/progmodes/elisp-mode-tests.el (xref--case-insensitive):
    New variable.
    (xref-elisp-test-run, emacs-test-dir): Only downcase if the
    filesystem seems to be case-insensitive.

diff --git a/test/lisp/progmodes/elisp-mode-tests.el 
b/test/lisp/progmodes/elisp-mode-tests.el
index 941e85b..97148ef 100644
--- a/test/lisp/progmodes/elisp-mode-tests.el
+++ b/test/lisp/progmodes/elisp-mode-tests.el
@@ -298,6 +298,16 @@ xref-elisp-test-descr-to-target
       )))
 
 
+;; tmp may be on a different filesystem to the tests, but, ehh.
+(defvar xref--case-insensitive
+  (let ((dir (make-temp-file "xref-test" t)))
+    (unwind-protect
+        (progn
+          (with-temp-file (expand-file-name "hElLo" dir) "hello")
+          (file-exists-p (expand-file-name "HELLO" dir)))
+      (delete-directory dir t)))
+  "Non-nil if file system seems to be case-insensitive.")
+
 (defun xref-elisp-test-run (xrefs expected-xrefs)
   (should (= (length xrefs) (length expected-xrefs)))
   (while xrefs
@@ -307,11 +317,13 @@ xref-elisp-test-run
            (expected-source (when (consp expected) (cdr expected))))
 
       ;; Downcase the filenames for case-insensitive file systems.
-      (setf (xref-elisp-location-file (oref xref location))
-            (downcase (xref-elisp-location-file (oref xref location))))
+      (when xref--case-insensitive
+        (setf (xref-elisp-location-file (oref xref location))
+              (downcase (xref-elisp-location-file (oref xref location))))
 
-      (setf (xref-elisp-location-file (oref expected-xref location))
-            (downcase (xref-elisp-location-file (oref expected-xref 
location))))
+        (setf (xref-elisp-location-file (oref expected-xref location))
+              (downcase (xref-elisp-location-file
+                         (oref expected-xref location)))))
 
       (should (equal xref expected-xref))
 
@@ -346,10 +358,10 @@ xref-elisp-deftest
 ;; `load-path' has the correct case, so this causes the expected test
 ;; values to have the wrong case). This is handled in
 ;; `xref-elisp-test-run'.
-(defconst emacs-test-dir
-  (downcase
-   (file-truename (file-name-directory
-                  (or load-file-name (buffer-file-name))))))
+(defvar emacs-test-dir
+  (funcall (if xref--case-insensitive 'downcase 'identity)
+           (file-truename (file-name-directory
+                           (or load-file-name (buffer-file-name))))))
 
 
 ;; alphabetical by test name