patch 8.2.3153: URLs with a dash in the scheme are not recognized

Problem:    URLs with a dash in the scheme are not recognized.
Solution:   Allow for a scheme with a dash, but not at the start or end.
            (Tsuyoshi CHO, closes #8299)

src/testdir/test_buffer.vim

@@ -381,6 +381,35 @@ func Test_balt()
   call assert_equal('OtherBuffer', bufname())
 endfunc
 
+" Test for buffer match URL(scheme) check
+" scheme is alpha and inner hyphen only.
+func Test_buffer_scheme()
+  CheckMSWindows
+
+  set noshellslash
+  %bwipe!
+  let bufnames = [
+    \ #{id: 'b0', name: 'test://xyz/foo/b0'    , match: 1},
+    \ #{id: 'b1', name: 'test+abc://xyz/foo/b1', match: 0},
+    \ #{id: 'b2', name: 'test_abc://xyz/foo/b2', match: 0},
+    \ #{id: 'b3', name: 'test-abc://xyz/foo/b3', match: 1},
+    \ #{id: 'b4', name: '-test://xyz/foo/b4'   , match: 0},
+    \ #{id: 'b5', name: 'test-://xyz/foo/b5'   , match: 0},
+    \]
+  for buf in bufnames
+    new `=buf.name`
+    if buf.match
+      call assert_equal(buf.name,    getbufinfo(buf.id)[0].name)
+    else
+      " slashes will have become backslashes
+      call assert_notequal(buf.name, getbufinfo(buf.id)[0].name)
+    endif
+    bwipe
+  endfor
+
+  set shellslash&
+endfunc
+
 " Test for the 'maxmem' and 'maxmemtot' options
 func Test_buffer_maxmem()
   " use 1KB per buffer and 2KB for all the buffers