Improve the rbenv prompt by using `version-name`

Prior to this, the rbenv prompt only showed something if the
$RBENV_VERSION environment variable was set. This was not a complete
solution because rbenv can be configured locally, per directory, with
dotfiles. When using dotfiles, the $RBENV_VERSION variables is not set.

This fixes the issue by taking the output of the `rbenv version-name`
command which shows the real rbenv version being used based on any of
the 4 ways to change rbenv as shown here:

https://github.com/rbenv/rbenv#choosing-the-ruby-version

If the current version of Ruby being used is the same as the global
Ruby, nothing is shown.

This commit also adds documentation to the README that describes the
prompt.

Fixes issue #215

1 files changed, 10 insertions, 2 deletions

diff --git a/powerlevel9k.zsh-theme b/powerlevel9k.zsh-theme
index 76ff5497..d0ce097c 100755
--- a/powerlevel9k.zsh-theme
+++ b/powerlevel9k.zsh-theme
@@ -605,8 +605,16 @@ prompt_ram() {
 
 # rbenv information
 prompt_rbenv() {
-  if [[ -n "$RBENV_VERSION" ]]; then
-    "$1_prompt_segment" "$0" "$2" "red" "$DEFAULT_COLOR" "$RBENV_VERSION" 'RUBY_ICON'
+  if which rbenv 2>/dev/null >&2; then
+    local rbenv_version_name="$(rbenv version-name)"
+    local rbenv_global="$(rbenv global)"
+
+    # Don't show anything if the current Ruby is the same as the global Ruby.
+    if [[ $rbenv_version_name == $rbenv_global ]]; then
+      return
+    fi
+
+    "$1_prompt_segment" "$0" "$2" "red" "$DEFAULT_COLOR" "$rbenv_version_name" 'RUBY_ICON'
   fi
 }