Use latest as default version

.changes/nextrelease/feature-default-version.json

@@ -0,0 +1,7 @@
+[
+  {
+    "type": "feature",
+    "category": "",
+    "description": "Removes validation of supplying the `version` configuration option to client constructors, defaulting to 'latest'`"
+  }
+]

src/ClientResolver.php

@@ -98,8 +98,8 @@ class ClientResolver
         'version' => [
             'type'     => 'value',
             'valid'    => ['string'],
-            'required' => [__CLASS__, '_missing_version'],
             'doc'      => 'The version of the webservice to utilize (e.g., 2006-03-01).',
+            'default' => 'latest',
         ],
         'signature_provider' => [
             'type'    => 'value',
@@ -1137,33 +1137,6 @@ public static function _default_signing_region(array &$args)
             : $args['region'];
     }
 
-    public static function _missing_version(array $args)
-    {
-        $service = isset($args['service']) ? $args['service'] : '';
-        $versions = ApiProvider::defaultProvider()->getVersions($service);
-        $versions = implode("\n", array_map(function ($v) {
-            return "* \"$v\"";
-        }, $versions)) ?: '* (none found)';
-
-        return <<<EOT
-A "version" configuration value is required. Specifying a version constraint
-ensures that your code will not be affected by a breaking change made to the
-service. For example, when using Amazon S3, you can lock your API version to
-"2006-03-01".
-
-Your build of the SDK has the following version(s) of "{$service}": {$versions}
-
-You may provide "latest" to the "version" configuration value to utilize the
-most recent available API version that your client's API provider can find.
-Note: Using 'latest' in a production application is not recommended.
-
-A list of available API versions can be found on each client's API documentation
-page: http://docs.aws.amazon.com/aws-sdk-php/v3/api/index.html. If you are
-unable to load a specific API version, then you may need to update your copy of
-the SDK.
-EOT;
-    }
-
     public static function _missing_region(array $args)
     {
         $service = isset($args['service']) ? $args['service'] : '';

tests/ClientResolverTest.php

@@ -752,27 +752,25 @@ public function testSkipsNonRequiredKeys()
         $r->resolve([], new HandlerList());
     }
 
-    public function testHasSpecificMessageForMissingVersion()
+    public function testAppliesLatestAsDefaultVersionWithoutSuppliedVersion()
     {
-        $this->expectExceptionMessage("A \"version\" configuration value is required");
-        $this->expectException(\InvalidArgumentException::class);
-        $args = ClientResolver::getDefaultArguments()['version'];
-        $r = new ClientResolver(['version' => $args]);
-        $r->resolve(['service' => 'foo'], new HandlerList());
+        $r = new ClientResolver(ClientResolver::getDefaultArguments());
+        $conf = $r->resolve([
+            'service' => 'ec2',
+            'region' => 'us-west-2',
+        ], new HandlerList());
+        self::assertSame('latest', $conf['version']);
     }
 
-    public function testHasSpecificMessageForNullRequiredVersion()
+    public function testAppliesVersion()
     {
-        $this->expectExceptionMessage("A \"version\" configuration value is required");
-        $this->expectException(\InvalidArgumentException::class);
         $r = new ClientResolver(ClientResolver::getDefaultArguments());
-        $list = new HandlerList();
-        $r->resolve([
-            'service' => 'foo',
-            'region' => 'x',
-            'credentials' => ['key' => 'a', 'secret' => 'b'],
-            'version' => null,
-        ], $list);
+        $conf = $r->resolve([
+            'service' => 'ec2',
+            'region' => 'us-west-2',
+            'version' => '2015-10-01'
+        ], new HandlerList());
+        self::assertSame('2015-10-01', $conf['version']);
     }
 
     public function testHasSpecificMessageForMissingRegion()