Add Imenu support to CSS mode and its derivatives

* lisp/textmodes/css-mode.el (css--join-nested-selectors)
(css--prev-index-position, css--extract-index-name): New helper
functions for supporting Imenu.
(css-mode): Set `imenu-space-replacement',
`imenu-prev-index-position-function', and
`imenu-extract-index-name-function'.
(css-current-defun-name): Reuse `css--prev-index-position' and
`css--extract-index-name' to support nested selectors.

* test/lisp/textmodes/css-mode-tests.el (css-test-current-defun-name):
Fix character index.
(css-test-join-nested-selectors): New tests for
`css--join-nested-selectors'.

* etc/NEWS: Add news entry.

1 files changed, 14 insertions, 1 deletions

diff --git a/test/lisp/textmodes/css-mode-tests.el b/test/lisp/textmodes/css-mode-tests.el
index b0283bfa455..bfae1bf2f75 100644
--- a/test/lisp/textmodes/css-mode-tests.el
+++ b/test/lisp/textmodes/css-mode-tests.el
@@ -85,7 +85,7 @@
     (insert "body { top: 0; }")
     (goto-char 7)
     (should (equal (css-current-defun-name) "body"))
-    (goto-char 18)
+    (goto-char 15)
     (should (equal (css-current-defun-name) "body"))))
 
 (ert-deftest css-test-current-defun-name-nested ()
@@ -324,6 +324,19 @@
     (css-cycle-color-format)
     (should (equal (buffer-string) "black"))))
 
+(ert-deftest css-test-join-nested-selectors ()
+  (should (equal (css--join-nested-selectors '("div" "&:hover"))
+                 "div:hover"))
+  (should
+   (equal (css--join-nested-selectors '("a" "&::before, &::after"))
+          "a::before, a::after"))
+  (should
+   (equal (css--join-nested-selectors
+           '("article" "& > .front-page" "& h1, & h2"))
+          "article > .front-page h1, article > .front-page h2"))
+  (should (equal (css--join-nested-selectors '(".link" "& + &"))
+                 ".link + .link")))
+
 (ert-deftest css-mdn-symbol-guessing ()
   (dolist (item '(("@med" "ia" "@media")
                   ("@keyframes " "{" "@keyframes")