More helpful error message when env's base version is not installed (#454)

bin/pyenv-virtualenv

@@ -336,10 +336,20 @@ fi
 # Set VERSION_NAME as default version in this script
 export PYENV_VERSION="${VERSION_NAME}"
 
+not_installed_message() {
+    local is_available=$(python-build --definitions | grep -F -x "$1")
+    echo "pyenv-virtualenv: \`${1}' is not installed in pyenv." 1>&2
+    if [[ $is_available ]]; then
+        echo "Run \`pyenv install ${1}' to install it." 1>&2
+    else
+        echo "It does not look like a valid Python version. See \`pyenv install --list' for available versions." 1>&2
+    fi
+}
+
 # Source version must exist before creating virtualenv.
 PREFIX="$(pyenv-prefix 2>/dev/null || true)"
 if [ ! -d "${PREFIX}" ]; then
-  echo "pyenv-virtualenv: \`${PYENV_VERSION}' is not installed in pyenv." 1>&2
+  not_installed_message "${PYENV_VERSION}"
   exit 1
 fi
 
@@ -441,7 +451,8 @@ else
           if [ -x "${python}" ]; then
             VIRTUALENV_OPTIONS[${#VIRTUALENV_OPTIONS[*]}]="--python=${python}"
           else
-            echo "pyenv-virtualenv: \`${VIRTUALENV_PYTHON##*/}' is not installed in pyenv." 1>&2
+            # echo "pyenv-virtualenv: \`${VIRTUALENV_PYTHON##*/}' is not installed in pyenv." 1>&2
+            not_installed_message "${VIRTUALENV_PYTHON##*/}"
             exit 1
           fi
         fi

test/python.bats

@@ -14,6 +14,7 @@ setup() {
   stub pyenv-rehash " : true"
   stub pyenv-version-name "echo \${PYENV_VERSION}"
   stub curl true
+  stub python-build "echo python2.7"
 }
 
 teardown() {
@@ -22,6 +23,7 @@ teardown() {
   unstub pyenv-prefix
   unstub pyenv-hooks
   unstub pyenv-rehash
+  unstub python-build
   teardown_version "2.7.8"
   rm -fr "$TMP"/*
 }
@@ -96,6 +98,7 @@ OUT
 
   assert_output <<OUT
 pyenv-virtualenv: \`python2.7' is not installed in pyenv.
+Run \`pyenv install python2.7' to install it.
 OUT
   assert_failure
 
@@ -106,3 +109,13 @@ OUT
   remove_executable "2.7.8" "python2.7"
   remove_executable "2.7.9" "python2.7"
 }
+
+@test "invalid python name" {
+  run pyenv-virtualenv --verbose --python=99.99.99 venv
+
+  assert_output <<OUT
+pyenv-virtualenv: \`99.99.99' is not installed in pyenv.
+It does not look like a valid Python version. See \`pyenv install --list' for available versions.
+OUT
+  assert_failure
+}