Implement lowercase-r replace in fish_vi_mode

Fixes #1595

share/functions/fish_mode_prompt.fish

@@ -9,6 +9,9 @@ function fish_mode_prompt --description "Displays the current mode"
       case insert
         set_color --bold --background green white
         echo '[I]'
+      case replace-one
+        set_color --bold --background green white
+        echo '[R]'
       case visual
         set_color --bold --background magenta white
         echo '[V]'

share/functions/fish_vi_key_bindings.fish

@@ -198,7 +198,13 @@ function fish_vi_key_bindings --description 'vi-like key bindings for fish'
 
   bind -M insert \ef forward-word
 
+  #
+  # Lowercase r, enters replace-one mode
+  #
 
+  bind -m replace-one r force-repaint
+  bind -M replace-one -m default '' delete-char self-insert backward-char force-repaint
+  bind -M replace-one -m default \e cancel force-repaint
 
   #
   # visual mode

tests/bind.expect

@@ -27,6 +27,16 @@ expect_prompt -re {\r\nsuccess\r\n} {
     puts stderr "Couldn't find expected output 'success'"
 }
 
+# Test lowercase-r replace
+send_line "\033ddiecho TEXT\033hhrAi"
+expect_prompt -re {\r\nTAXT\r\n} {
+    puts "replace success"
+} -nounmatched -re {\r\nfail} {
+    puts stderr "replace fail"
+} unmatched {
+    puts stderr "Couldn't find expected output 'TAXT'"
+}
+
 # still in insert mode, switch back to regular key bindings
 send_line "set -g fish_key_bindings fish_default_key_bindings"
 expect_prompt

tests/bind.expect.out

@@ -1,3 +1,4 @@
 success
 success
+replace success
 success