Shell: Don't reset 'last_return_code' before running commands

Some variables depend on its value to function correctly.
Fixes the following issue:
    $ false; echo $?
    1
    $ false
    $ echo $?
    128

Userland/Shell/AST.cpp

@@ -3564,7 +3564,7 @@ Vector<String> SpecialVariableValue::resolve_as_list(RefPtr<Shell> shell)
 
     switch (m_name) {
     case '?':
-        return { resolve_slices(shell, String::number(shell->last_return_code), m_slices) };
+        return { resolve_slices(shell, String::number(shell->last_return_code.value_or(0)), m_slices) };
     case '$':
         return { resolve_slices(shell, String::number(getpid()), m_slices) };
     case '*':

Userland/Shell/Builtin.cpp

@@ -1059,7 +1059,7 @@ int Shell::builtin_not(int argc, const char** argv)
     }
     // In case it was a function.
     if (!found_a_job)
-        exit_code = last_return_code;
+        exit_code = last_return_code.value_or(0);
     return exit_code == 0 ? 1 : 0;
 }
 

Userland/Shell/Shell.cpp

@@ -469,7 +469,7 @@ bool Shell::invoke_function(const AST::Command& command, int& retval)
 
     (void)function.body->run(*this);
 
-    retval = last_return_code;
+    retval = last_return_code.value_or(0);
     return true;
 }
 
@@ -536,8 +536,8 @@ int Shell::run_command(StringView cmd, Optional<SourcePosition> source_position_
 
     take_error();
 
-    // If we end up executing nothing, let's return a failing exit code.
-    last_return_code = 128;
+    if (!last_return_code.has_value())
+        last_return_code = 0;
 
     ScopedValueRollback source_position_rollback { m_source_position };
     if (source_position_override.has_value())
@@ -581,7 +581,7 @@ int Shell::run_command(StringView cmd, Optional<SourcePosition> source_position_
         return 1;
     }
 
-    return last_return_code;
+    return last_return_code.value_or(0);
 }
 
 ErrorOr<RefPtr<Job>> Shell::run_command(const AST::Command& command)
@@ -595,7 +595,7 @@ ErrorOr<RefPtr<Job>> Shell::run_command(const AST::Command& command)
     if (command.argv.is_empty() && !command.should_immediately_execute_next) {
         m_global_redirections.extend(command.redirections);
         for (auto& next_in_chain : command.next_chain)
-            run_tail(command, next_in_chain, last_return_code);
+            run_tail(command, next_in_chain, last_return_code.value_or(0));
         return nullptr;
     }
 
@@ -668,9 +668,10 @@ ErrorOr<RefPtr<Job>> Shell::run_command(const AST::Command& command)
     for (auto& redirection : command.redirections)
         TRY(resolve_redirection(redirection));
 
-    if (command.should_wait && run_builtin(command, rewirings, last_return_code)) {
+    if (int local_return_code = 0; command.should_wait && run_builtin(command, rewirings, local_return_code)) {
+        last_return_code = local_return_code;
         for (auto& next_in_chain : command.next_chain)
-            run_tail(command, next_in_chain, last_return_code);
+            run_tail(command, next_in_chain, *last_return_code);
         return nullptr;
     }
 
@@ -681,9 +682,10 @@ ErrorOr<RefPtr<Job>> Shell::run_command(const AST::Command& command)
         for (auto& rewiring : rewirings)
             TRY(Core::System::dup2(rewiring.old_fd, rewiring.new_fd));
 
-        if (invoke_function(command, last_return_code)) {
+        if (int local_return_code = 0; invoke_function(command, local_return_code)) {
+            last_return_code = local_return_code;
             for (auto& next_in_chain : command.next_chain)
-                run_tail(command, next_in_chain, last_return_code);
+                run_tail(command, next_in_chain, *last_return_code);
             return nullptr;
         }
     }
@@ -695,7 +697,7 @@ ErrorOr<RefPtr<Job>> Shell::run_command(const AST::Command& command)
         && command.next_chain.first().node->should_override_execution_in_current_process()) {
 
         for (auto& next_in_chain : command.next_chain)
-            run_tail(command, next_in_chain, last_return_code);
+            run_tail(command, next_in_chain, last_return_code.value_or(0));
         return nullptr;
     }
 
@@ -752,14 +754,14 @@ ErrorOr<RefPtr<Job>> Shell::run_command(const AST::Command& command)
             for (auto& next_in_chain : command.next_chain)
                 run_tail(command, next_in_chain, 0);
 
-            _exit(last_return_code);
+            _exit(last_return_code.value_or(0));
         }
 
-        if (run_builtin(command, {}, last_return_code))
-            _exit(last_return_code);
+        if (int local_return_code = 0; run_builtin(command, {}, local_return_code))
+            _exit(local_return_code);
 
-        if (invoke_function(command, last_return_code))
-            _exit(last_return_code);
+        if (int local_return_code = 0; invoke_function(command, local_return_code))
+            _exit(local_return_code);
 
         // We no longer need the jobs here.
         jobs.clear();

Userland/Shell/Shell.h

@@ -212,7 +212,7 @@ public:
     char hostname[HostNameSize];
 
     uid_t uid;
-    int last_return_code { 0 };
+    Optional<int> last_return_code;
     Vector<String> directory_stack;
     CircularQueue<String, 8> cd_history; // FIXME: have a configurable cd history length
     HashMap<u64, NonnullRefPtr<Job>> jobs;