[issue-2170] Modified runLocally function to accept closure

As noted in the issue deployphp#2170, the logic in the recipe/check_remote.php
would try to get the binary path of local and remote git executable.

However, due to specific implementation, the get('bin/git') would
have been called twice in the context of remote host, instead of
invoking it once on remote and once on local machine.

The runLocally function has thus been reworked, to accept Closure,
which will be invoked in the context of the localhost machine.
Once a Closure has been passed, the function will push the Localhost
to the Context, invoke the closure, store the stdout (if available),
pop the Localhost from the Context and finally return the stdout.

For compatibility reasons, the function also accepts the string argument,
however it is wrapped in a closure and once again passed to the runLocally
function.

The recipe/check_remote.php file has been reworked, to utilize the Closure,
to make sure that the get('bin/git') is being called in the Localhost context.

recipe/deploy/check_remote.php

@@ -39,7 +39,10 @@
             $opt = '--heads';
         }
 
-        $remoteLs = runLocally(sprintf("%s ls-remote $opt $repository $ref", get('bin/git')));
+        $remoteLs = runLocally(function () use ($opt, $repository, $ref) {
+            $cmd = sprintf("%s ls-remote $opt $repository $ref", get('bin/git'));
+            return run($cmd);
+        });
         if (strstr($remoteLs, "\n")) {
             throw new Exception("Could not determine target revision. '$ref' matched multiple commits.");
         }

src/functions.php

@@ -7,6 +7,7 @@
 
 namespace Deployer;
 
+use Closure;
 use Deployer\Exception\Exception;
 use Deployer\Exception\GracefulShutdownException;
 use Deployer\Exception\RunException;
@@ -339,24 +340,43 @@ function run($command, $options = [])
 /**
  * Execute commands on local machine
  *
- * @param string $command Command to run locally.
+ * @param string|Closure $command Command to run locally, or a closure that will be executed in local machine context
  * @param array $options
  * @return string Output of command.
  */
 function runLocally($command, $options = [])
 {
-    $process = Deployer::get()->processRunner;
-    $command = parse($command);
+    if ($command instanceof Closure) {
+        $input = Context::has() ? input() : null;
+        $output = Context::has() ? output() : null;
 
-    $env = array_merge_alternate(get('env', []), $options['env'] ?? []);
-    if (!empty($env)) {
-        $env = array_to_string($env);
-        $command = "export $env; $command";
-    }
+        $localhostContext = new Context(new Localhost(), $input, $output);
+        Context::push($localhostContext);
+        try {
+            $output = $command();
+            if (!is_string($output)) {
+                $output = '';
+            }
+        } finally {
+            Context::pop();
+        }
+
+        $output = rtrim($output);
+        return $output;
+    } else {
+        $command = parse($command);
+        $env = array_merge_alternate(get('env', []), $options['env'] ?? []);
 
-    $output = $process->run(new Localhost(), $command, $options);
+        return runLocally(function () use ($command, $options, $env) {
+            if (!empty($env)) {
+                $env = array_to_string($env);
+                $command = "export $env; $command";
+            }
 
-    return rtrim($output);
+            $output = run($command, $options);
+            return $output;
+        });
+    }
 }
 
 /**