themes/agnoster : Detect and show pyenv information (#458)

 - if pyenv is not initialized, fall back to the virtualenv detection
 - when pyenv is set to a version other than "system", show the version number
 - when pyenv is in virtulenv mode, also display the virtualenv's name

Co-authored-by: Koichi Murase <myoga.murase@gmail.com>

themes/agnoster/agnoster.theme.sh

@@ -283,6 +283,9 @@ function prompt_end {
 
 ### virtualenv prompt
 function prompt_virtualenv {
+  # Exclude pyenv
+  [[ $PYENV_VIRTUALENV_INIT == 1 ]] && _omb_util_binary_exists pyenv && return 0
+
   if [[ -d $VIRTUAL_ENV ]]; then
     # Python could output the version information in both stdout and
     # stderr (e.g. if using pyenv, the output goes to stderr).
@@ -296,6 +299,29 @@ function prompt_virtualenv {
   fi
 }
 
+### pyenv prompt
+function prompt_pyenv {
+  if [[ $PYENV_VIRTUALENV_INIT == 1 ]] && _omb_util_binary_exists pyenv; then
+    # Priority is shell > local > global
+    # When pyenv shell is set, the environment variable $PYENV_VERSION is set with the value we want
+    if [[ ! ${PYENV_VERSION-} ]]; then
+      # If not set, fall back to pyenv local/global to get the version
+      local PYENV_VERSION=$(pyenv local 2>/dev/null || pyenv global 2>/dev/null)
+    fi
+    # If it is not the system's python, then display additional info
+    if [[ "$PYENV_VERSION" != "system" ]]; then
+      # It's a pyenv virtualenv, get the version number
+      if [[ -d $PYENV_VIRTUAL_ENV ]]; then
+        local VERSION_OUTPUT=$("$PYENV_VIRTUAL_ENV"/bin/python --version 2>&1)
+        local PYENV_VENV_VERSION=$(awk '{print $NF}' <<< "$VERSION_OUTPUT")
+        prompt_segment cyan white "[$PYENV_VERSION] $(basename "$PYENV_VENV_VERSION")"
+      else
+        prompt_segment cyan white "$PYENV_VERSION"
+      fi
+    fi
+  fi
+}
+
 ### conda env prompt
 function prompt_condaenv {
   if [[ -d $CONDA_PREFIX ]]; then
@@ -534,6 +560,7 @@ function build_prompt {
   [[ -z ${AG_NO_CONTEXT+x} ]] && prompt_context
   if [[ ${OMB_PROMPT_SHOW_PYTHON_VENV-} ]]; then
     prompt_virtualenv
+    prompt_pyenv
     prompt_condaenv
   fi
   prompt_dir