launcher: add a requirements framework to declare version dependencies

Currently we don't have a way for the checked out repo version to
declare the version of tools it needs before we start running it.
For somethings, like git, it's not a big deal as it can handle all
the asserts itself.  But for things like Python, it's impossible
to reliably check before executing.

We're in this state now:
- we've been allowing Python 3.4, so the launcher accepts it
- the repo codebase starts using Python 3.6 features
- launcher tries to import us but hits syntax errors
- user is left confused and assuming new repo is broken because
  they're seeing syntax errors

This scenario is playing out with old launchers that still accept
Python 2, and will continue to play out as time goes on and we want
to require newer versions of Python 3.

Lets create a JSON file to declare all these system requirements.
That file format is extremely stable, so loading & parsing from
even ancient versions of Python shouldn't be a problem.  Then the
launcher can read these settings and check the system state before
attempting to execute any code.  If the tools are too old, it can
clearly diagnose & display information to the user as to the real
problem (and not emit tracebacks or syntax errors).

We have a couple of different tool version checks already (git,
python, ssh) and can harmonize them in a single place.

This also allows us to assert a reverse dependency if the need
ever comes up: force the user to upgrade their `repo` launcher
before we'll let them run us.  Even though the launcher warns
whenever a newer release is available, some users seem to ignore
that, or they don't use repo that often (on the scale of years),
and their upgrade jump is so dramatic that they fall back into
the syntax error pit.

Hopefully by the end of the year we can assume enough people
have upgraded their launcher such that we can delete all of the
duplicate version checks in the codebase.  But until then, we'll
keep them to maintain coverage.

Change-Id: I5c12bbffdfd0a8ce978f39aa7f4674026fe9f4f8
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/293003
Reviewed-by: Michael Mortensen <mmortensen@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/tests/test_wrapper.py b/tests/test_wrapper.py
index d8713738..6400faf4 100644
--- a/tests/test_wrapper.py
+++ b/tests/test_wrapper.py
@@ -19,6 +19,7 @@ from io import StringIO
 import os
 import re
 import shutil
+import sys
 import tempfile
 import unittest
 from unittest import mock
@@ -255,6 +256,81 @@ class CheckGitVersion(RepoWrapperTestCase):
       self.wrapper._CheckGitVersion()
 
 
+class Requirements(RepoWrapperTestCase):
+  """Check Requirements handling."""
+
+  def test_missing_file(self):
+    """Don't crash if the file is missing (old version)."""
+    testdir = os.path.dirname(os.path.realpath(__file__))
+    self.assertIsNone(self.wrapper.Requirements.from_dir(testdir))
+    self.assertIsNone(self.wrapper.Requirements.from_file(
+        os.path.join(testdir, 'xxxxxxxxxxxxxxxxxxxxxxxx')))
+
+  def test_corrupt_data(self):
+    """If the file can't be parsed, don't blow up."""
+    self.assertIsNone(self.wrapper.Requirements.from_file(__file__))
+    self.assertIsNone(self.wrapper.Requirements.from_data(b'x'))
+
+  def test_valid_data(self):
+    """Make sure we can parse the file we ship."""
+    self.assertIsNotNone(self.wrapper.Requirements.from_data(b'{}'))
+    rootdir = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
+    self.assertIsNotNone(self.wrapper.Requirements.from_dir(rootdir))
+    self.assertIsNotNone(self.wrapper.Requirements.from_file(os.path.join(
+        rootdir, 'requirements.json')))
+
+  def test_format_ver(self):
+    """Check format_ver can format."""
+    self.assertEqual('1.2.3', self.wrapper.Requirements._format_ver((1, 2, 3)))
+    self.assertEqual('1', self.wrapper.Requirements._format_ver([1]))
+
+  def test_assert_all_unknown(self):
+    """Check assert_all works with incompatible file."""
+    reqs = self.wrapper.Requirements({})
+    reqs.assert_all()
+
+  def test_assert_all_new_repo(self):
+    """Check assert_all accepts new enough repo."""
+    reqs = self.wrapper.Requirements({'repo': {'hard': [1, 0]}})
+    reqs.assert_all()
+
+  def test_assert_all_old_repo(self):
+    """Check assert_all rejects old repo."""
+    reqs = self.wrapper.Requirements({'repo': {'hard': [99999, 0]}})
+    with self.assertRaises(SystemExit):
+      reqs.assert_all()
+
+  def test_assert_all_new_python(self):
+    """Check assert_all accepts new enough python."""
+    reqs = self.wrapper.Requirements({'python': {'hard': sys.version_info}})
+    reqs.assert_all()
+
+  def test_assert_all_old_repo(self):
+    """Check assert_all rejects old repo."""
+    reqs = self.wrapper.Requirements({'python': {'hard': [99999, 0]}})
+    with self.assertRaises(SystemExit):
+      reqs.assert_all()
+
+  def test_assert_ver_unknown(self):
+    """Check assert_ver works with incompatible file."""
+    reqs = self.wrapper.Requirements({})
+    reqs.assert_ver('xxx', (1, 0))
+
+  def test_assert_ver_new(self):
+    """Check assert_ver allows new enough versions."""
+    reqs = self.wrapper.Requirements({'git': {'hard': [1, 0], 'soft': [2, 0]}})
+    reqs.assert_ver('git', (1, 0))
+    reqs.assert_ver('git', (1, 5))
+    reqs.assert_ver('git', (2, 0))
+    reqs.assert_ver('git', (2, 5))
+
+  def test_assert_ver_old(self):
+    """Check assert_ver rejects old versions."""
+    reqs = self.wrapper.Requirements({'git': {'hard': [1, 0], 'soft': [2, 0]}})
+    with self.assertRaises(SystemExit):
+      reqs.assert_ver('git', (0, 5))
+
+
 class NeedSetupGnuPG(RepoWrapperTestCase):
   """Check NeedSetupGnuPG behavior."""