Fix system_get_info() for non-installed modules

Thanks, @alexpott.

+++ b/core/modules/system/tests/src/Kernel/System/SystemGetInfoTest.php
@@ -0,0 +1,31 @@
+    $this->assertEquals([], system_get_info('module', 'user'));

Should be assertSame().

This looks like a proper bugfix! Thank you for the detailed test coverage.

+++ b/core/modules/system/system.module
@@ -963,7 +963,12 @@ function system_get_info($type, $name = NULL) {
+      catch (\InvalidArgumentException $e) {
+        return [];
+      }

Just a general comment: Wouldn't it be nice to have a dedicated exception type for this?

Running the test without the changes to system.module I got this, which seems appropriate:

$ ./vendor/bin/phpunit -c core/ --testsuite kernel --filter SystemGetInfoTest
PHPUnit 4.8.36 by Sebastian Bergmann and contributors.

Testing 
E

Time: 12.72 seconds, Memory: 38.00MB

There was 1 error:

1) Drupal\Tests\system\Kernel\System\SystemGetInfoTest::testSystemGetInfo
InvalidArgumentException: The module user does not exist or is not installed.

Also it's nice to get coverage for themes.

In #3, I meant that assertSame() was needed for checking against an expected empty array, but changing them all to assertSame() is fine, too. :-)

And.... I can install ajax_example, which was my original issue: #2208429-340: Extension System, Part III: ExtensionList, ModuleExtensionList and ProfileExtensionList

So this LGTM.

Re: #6, we should really deprecate system_get_info() for something else rather than changing its return values.

Most failure in #2659940: Extension System, Part III: ThemeExtensionList and ThemeEngineExtensionList right now are actually triggered and prevented by this patch.

Most failure in #2659940: Extension System, Part III: ThemeExtensionList right now are actually triggered and prevented by this patch.

I believe this to be the case also. So just waiting for this patch to be committed.

I agree with #6 - can we get a follow up for that?

Adding review credit for @Mile23

Committed 38c2ac7 and pushed to 8.6.x.
Thanks!

Someone just added a pile of deprecations around this: #2940190: [meta] Deprecations of old functions in Extension system and #2940189: Deprecate system_get_info()

I agree with #6 - can we get a follow up for that?

Created #2940203: Use dedicated Exception classes for extension system for that.