Add smoke test that Android SDK is installed properly

The Android SDK installation states often have tricky changes
due to upstream changes by Google,
and additionally often fail silently in various different ways
e.g. because the `android` tool always has a zero exit status.
Additionally, some failures are not evident until Servo builds
themselves start failing.

Add a somke test in saltfs to catch common problems early on,
and automatically run it on Travis.

.travis/dispatch.sh

@@ -72,6 +72,9 @@ else
     if [[ "${SALT_NODE_ID}" == "servo-master1" ]]; then
         ./test.py sls.buildbot.master sls.homu sls.nginx
     fi
+    if [[ "${SALT_NODE_ID}" == "servo-linux-cross1" ]]; then
+        ./test.py sls.servo-build-dependencies.android
+    fi
 
     # Salt doesn't support timezone.system on OSX
     # See https://github.com/saltstack/salt/issues/31345

requirements.txt

@@ -2,3 +2,4 @@
 # (Travis-CI will auto-install them from this file)
 flake8 == 2.5.4
 toml == 0.9.1  # Please ensure this is in sync with homu/init.sls
+jinja2 == 2.9.6  # TODO: sync this with version used by Salt

tests/sls/servo-build-dependencies/android/sdk.py

@@ -0,0 +1,88 @@
+import os.path
+
+from jinja2 import Template
+
+from tests.util import Failure, Success, project_path
+
+BASE_DIR = '/home/servo/android/sdk'
+CHECKS = {
+    '{}/android-sdk-linux': {'type': 'absent'},
+    '{}/tools/android': {'type': 'file', 'executable': True},
+    '{}/platform-tools': {'type': 'directory'},
+    '{}/platforms/android-{platform}': {'type': 'directory'},
+    '{}/build-tools/{build_tools}': {'type': 'directory'},
+}
+
+
+def has_perms(perms, stat_info):
+    return perms == stat_info & perms
+
+
+def run():
+    with open(os.path.join(
+        project_path(),
+        'servo-build-dependencies',
+        'map.jinja'
+    )) as jinja_file:
+        template = Template(jinja_file.read())
+
+    sdk_vars = template.module.android['sdk']
+    failures = []
+    checks = {}
+    for version, sdk in sdk_vars.items():
+        if version == 'current':
+            if sdk not in sdk_vars:
+                failures.append(
+                    'The current SDK is not pointed at any installed SDK'
+                )
+                continue
+            checks[os.path.join(BASE_DIR, 'current')] = {
+                'type': 'link',
+                'target': os.path.join(BASE_DIR, sdk)
+            }
+            sdk = sdk_vars[sdk]
+        for path_template, spec in CHECKS.items():
+            path = path_template.format(os.path.join(BASE_DIR, version), **sdk)
+            checks[path] = spec
+
+    for path, spec in sorted(checks.items(), key=lambda kv: kv[0]):
+        exists = os.path.lexists(path)
+        if spec['type'] == 'absent':
+            if exists:
+                failures.append('{} should not exist'.format(path))
+            continue
+        if not exists:
+            failures.append('{} does not exist but should'.format(path))
+            continue
+        info = os.stat(path).st_mode
+        if spec['type'] == 'directory':
+            if not (os.path.isdir(path) and not os.path.islink(path)):
+                failures.append('{} should be a directory'.format(path))
+            if not has_perms(0o700, info):
+                failures.append(
+                    '{} should have at least perms 700'.format(path)
+                )
+        elif spec['type'] == 'file':
+            if not (os.path.isfile(path) and not os.path.islink(path)):
+                failures.append('{} should be a file'.format(path))
+            perms = 0o700 if spec['executable'] else 0o600
+            if not has_perms(perms, info):
+                failures.append(
+                    '{} should have at least perms {:o}'.format(path, perms)
+                )
+        elif spec['type'] == 'link':
+            if not os.path.islink(path):
+                failures.append('{} should be a symlink'.format(path))
+            if not os.path.realpath(path) == spec['target']:
+                failures.append(
+                    '{} should be a link to {}'.format(path, spec['target'])
+                )
+
+        else:
+            failures.append('Unknown spec for path {}'.format(path))
+
+    if failures:
+        output = '\n'.join(('- {}'.format(f) for f in failures))
+        return Failure('Android SDK(s) not installed properly:', output)
+
+    return Success('Android SDK(s) are properly installed')