Allow for empty choice while selecting dependencies

Fixes #2355

This works around an issue with cleo's `Command.choice` implementation.
If the user does not make a selection then an AttributeError is raised.

src/poetry/console/commands/init.py

@@ -306,19 +306,26 @@ def _determine_requirements(
 
  self.line(info_string)
 
+ # Default to an empty value to signal no package was selected
+ choices.append("")
+
  package = self.choice(
  "\nEnter package # to add, or the complete package name if it"
  " is not listed",
  choices,
  attempts=3,
+ default=len(choices) - 1,
  )
 
+ if not package:
+ self.line("<warning>No package selected</warning>")
+
  # package selected by user, set constraint name to package name
- if package is not False:
+ if package:
  constraint["name"] = package
 
  # no constraint yet, determine the best version automatically
- if package is not False and "version" not in constraint:
+ if package and "version" not in constraint:
  question = self.create_question(
  "Enter the version constraint to require "
  "(or leave blank to use the latest version):"
@@ -340,7 +347,7 @@ def _determine_requirements(
 
  constraint["version"] = package_constraint
 
- if package is not False:
+ if package:
  result.append(constraint)
 
  if self.io.is_interactive():

tests/console/commands/test_init.py

@@ -177,6 +177,50 @@ def test_interactive_with_dependencies(tester: CommandTester, repo: TestReposito
  assert expected in tester.io.fetch_output()
 
 
+# Regression test for https://github.com/python-poetry/poetry/issues/2355
+def test_interactive_with_dependencies_and_no_selection(
+ tester: CommandTester, repo: TestRepository
+):
+ repo.add_package(get_package("django-pendulum", "0.1.6-pre4"))
+ repo.add_package(get_package("pendulum", "2.0.0"))
+ repo.add_package(get_package("pytest", "3.6.0"))
+
+ inputs = [
+ "my-package", # Package name
+ "1.2.3", # Version
+ "This is a description", # Description
+ "n", # Author
+ "MIT", # License
+ "~2.7 || ^3.6", # Python
+ "", # Interactive packages
+ "pendulu", # Search for package
+ "", # Do not select an option
+ "", # Stop searching for packages
+ "", # Interactive dev packages
+ "pytest", # Search for package
+ "", # Do not select an option
+ "",
+ "",
+ "\n", # Generate
+ ]
+ tester.execute(inputs="\n".join(inputs))
+ expected = """\
+[tool.poetry]
+name = "my-package"
+version = "1.2.3"
+description = "This is a description"
+authors = ["Your Name <you@example.com>"]
+license = "MIT"
+readme = "README.md"
+packages = [{include = "my_package"}]
+
+[tool.poetry.dependencies]
+python = "~2.7 || ^3.6"
+"""
+
+ assert expected in tester.io.fetch_output()
+
+
 def test_empty_license(tester: CommandTester):
  inputs = [
  "my-package", # Package name