Show project version if no argument provided for version command (#1191)

This changes the behavior of version command to show the current version
of the project if no arguments are provided.

docs/docs/cli.md

@@ -384,8 +384,9 @@ poetry lock
 
 ## version
 
-This command bumps the version of the project
-and writes the new version back to `pyproject.toml`
+This command shows the current version of the project or bumps the version of 
+the project and writes the new version back to `pyproject.toml` if a valid
+bump rule is provided.
 
 The new version should ideally be a valid semver string or a valid bump rule:
 `patch`, `minor`, `major`, `prepatch`, `preminor`, `premajor`, `prerelease`.

poetry/console/commands/version.py

@@ -6,20 +6,23 @@ from .command import Command
 class VersionCommand(Command):
 
     name = "version"
-    description = "Bumps the version of the project."
+    description = (
+        "Shows the version of the project or bumps it when a valid"
+        "bump rule is provided."
+    )
 
     arguments = [
         argument(
             "version",
             "The version number or the rule to update the version.",
             optional=True,
-            default="patch",
         )
     ]
 
     help = """\
-The version command bumps the version of the project
-and writes the new version back to <comment>pyproject.toml</>.
+The version command shows the current version of the project or bumps the version of 
+the project and writes the new version back to <comment>pyproject.toml</> if a valid
+bump rule is provided.
 
 The new version should ideally be a valid semver string or a valid bump rule:
 patch, minor, major, prepatch, preminor, premajor, prerelease.
@@ -38,7 +41,10 @@ patch, minor, major, prepatch, preminor, premajor, prerelease.
     def handle(self):
         version = self.argument("version")
 
-        version = self.increment_version(self.poetry.package.pretty_version, version)
+        if version:
+            version = self.increment_version(
+                self.poetry.package.pretty_version, version
+            )
 
             self.line(
                 "Bumping version from <comment>{}</> to <info>{}</>".format(
@@ -51,6 +57,12 @@ patch, minor, major, prepatch, preminor, premajor, prerelease.
             poetry_content["version"] = version.text
 
             self.poetry.file.write(content)
+        else:
+            self.line(
+                "Project (<comment>{}</>) version is <info>{}</>".format(
+                    self.poetry.package.name, self.poetry.package.pretty_version
+                )
+            )
 
     def increment_version(self, version, rule):
         from poetry.semver import Version

tests/console/commands/test_version.py

 import pytest
+from cleo import CommandTester
 
 from poetry.console.commands import VersionCommand
 
@@ -36,3 +37,10 @@ def command():
 )
 def test_increment_version(version, rule, expected, command):
     assert expected == command.increment_version(version, rule).text
+
+
+def test_version_show(app):
+    command = app.find("version")
+    tester = CommandTester(command)
+    tester.execute()
+    assert "Project (simple-project) version is 1.2.3\n" == tester.io.fetch_output()