From 8dd2d4f15d879484a1364d661e6526a9ec42c053 Mon Sep 17 00:00:00 2001
From: Soumya <soumyasr@google.com>
Date: Sat, 18 Jul 2020 10:25:43 -0700
Subject: [PATCH] Change builtins to return maybe_t<int> instead of int

---
 src/builtin.cpp             | 23 +++++++++++++----------
 src/builtin.h               |  2 +-
 src/builtin_argparse.cpp    |  2 +-
 src/builtin_argparse.h      |  4 +++-
 src/builtin_bg.cpp          |  2 +-
 src/builtin_bg.h            |  4 +++-
 src/builtin_bind.cpp        |  2 +-
 src/builtin_bind.h          |  4 ++--
 src/builtin_block.cpp       |  2 +-
 src/builtin_block.h         |  4 +++-
 src/builtin_builtin.cpp     |  2 +-
 src/builtin_builtin.h       |  4 +++-
 src/builtin_cd.cpp          |  2 +-
 src/builtin_cd.h            |  4 +++-
 src/builtin_command.cpp     |  2 +-
 src/builtin_command.h       |  4 +++-
 src/builtin_commandline.cpp |  2 +-
 src/builtin_commandline.h   |  2 +-
 src/builtin_complete.cpp    |  2 +-
 src/builtin_complete.h      |  2 +-
 src/builtin_contains.cpp    |  2 +-
 src/builtin_contains.h      |  4 +++-
 src/builtin_disown.cpp      |  2 +-
 src/builtin_disown.h        |  4 +++-
 src/builtin_echo.cpp        |  2 +-
 src/builtin_echo.h          |  4 +++-
 src/builtin_emit.cpp        |  2 +-
 src/builtin_emit.h          |  4 +++-
 src/builtin_eval.cpp        |  2 +-
 src/builtin_eval.h          |  4 +++-
 src/builtin_exit.cpp        |  2 +-
 src/builtin_exit.h          |  4 +++-
 src/builtin_fg.cpp          |  2 +-
 src/builtin_fg.h            |  4 +++-
 src/builtin_function.cpp    |  2 +-
 src/builtin_function.h      |  2 +-
 src/builtin_functions.cpp   |  2 +-
 src/builtin_functions.h     |  4 +++-
 src/builtin_history.cpp     |  2 +-
 src/builtin_history.h       |  4 +++-
 src/builtin_jobs.cpp        |  2 +-
 src/builtin_jobs.h          |  2 +-
 src/builtin_math.cpp        |  2 +-
 src/builtin_math.h          |  4 +++-
 src/builtin_printf.cpp      |  2 +-
 src/builtin_printf.h        |  2 +-
 src/builtin_pwd.cpp         |  2 +-
 src/builtin_pwd.h           |  4 +++-
 src/builtin_random.cpp      |  2 +-
 src/builtin_random.h        |  4 +++-
 src/builtin_read.cpp        |  2 +-
 src/builtin_read.h          |  4 +++-
 src/builtin_realpath.cpp    |  2 +-
 src/builtin_realpath.h      |  4 +++-
 src/builtin_return.cpp      |  2 +-
 src/builtin_return.h        |  4 +++-
 src/builtin_set.cpp         |  2 +-
 src/builtin_set.h           |  2 +-
 src/builtin_set_color.cpp   |  2 +-
 src/builtin_set_color.h     |  2 +-
 src/builtin_source.cpp      |  2 +-
 src/builtin_source.h        |  4 +++-
 src/builtin_status.cpp      |  2 +-
 src/builtin_status.h        |  4 +++-
 src/builtin_string.cpp      |  2 +-
 src/builtin_string.h        |  2 +-
 src/builtin_test.cpp        |  2 +-
 src/builtin_test.h          |  4 +++-
 src/builtin_ulimit.cpp      |  2 +-
 src/builtin_ulimit.h        |  2 +-
 src/builtin_wait.cpp        |  2 +-
 src/builtin_wait.h          |  4 +++-
 src/exec.cpp                |  6 +++++-
 src/fish_tests.cpp          | 20 ++++++++++++--------
 src/maybe.h                 |  1 +
 src/parse_execution.cpp     | 12 ++++++++----
 src/proc.cpp                | 24 ++++++++++++++++++++----
 src/proc.h                  | 18 ++++++++++++++++--
 78 files changed, 197 insertions(+), 101 deletions(-)

diff --git a/src/builtin.cpp b/src/builtin.cpp
index af5388ab4..14641071d 100644
--- a/src/builtin.cpp
+++ b/src/builtin.cpp
@@ -4,7 +4,7 @@
 //
 // 1). Create a function in builtin.c with the following signature:
 //
-//     <tt>static int builtin_NAME(parser_t &parser, io_streams_t &streams, wchar_t **argv)</tt>
+//     <tt>static maybe_t<int> builtin_NAME(parser_t &parser, io_streams_t &streams, wchar_t **argv)</tt>
 //
 // where NAME is the name of the builtin, and args is a zero-terminated list of arguments.
 //
@@ -201,7 +201,7 @@ void builtin_print_error_trailer(parser_t &parser, output_stream_t &b, const wch
 
 /// A generic bultin that only supports showing a help message. This is only a placeholder that
 /// prints the help message. Useful for commands that live in the parser.
-static int builtin_generic(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+static maybe_t<int> builtin_generic(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
@@ -228,7 +228,7 @@ static int builtin_generic(parser_t &parser, io_streams_t &streams, wchar_t **ar
 // Since this is just for counting, it can be massive.
 #define COUNT_CHUNK_SIZE (512 * 256)
 /// Implementation of the builtin count command, used to count the number of arguments sent to it.
-static int builtin_count(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+static maybe_t<int> builtin_count(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     UNUSED(parser);
     int argc = 0;
 
@@ -256,7 +256,7 @@ static int builtin_count(parser_t &parser, io_streams_t &streams, wchar_t **argv
 
 /// This function handles both the 'continue' and the 'break' builtins that are used for loop
 /// control.
-static int builtin_break_continue(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+static maybe_t<int> builtin_break_continue(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     int is_break = (std::wcscmp(argv[0], L"break") == 0);
     int argc = builtin_count_args(argv);
 
@@ -287,7 +287,7 @@ static int builtin_break_continue(parser_t &parser, io_streams_t &streams, wchar
 }
 
 /// Implementation of the builtin breakpoint command, used to launch the interactive debugger.
-static int builtin_breakpoint(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+static maybe_t<int> builtin_breakpoint(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     if (argv[1] != nullptr) {
         streams.err.append_format(BUILTIN_ERR_ARG_COUNT1, cmd, 0, builtin_count_args(argv) - 1);
@@ -313,21 +313,21 @@ static int builtin_breakpoint(parser_t &parser, io_streams_t &streams, wchar_t *
     return parser.get_last_status();
 }
 
-int builtin_true(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_true(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     UNUSED(parser);
     UNUSED(streams);
     UNUSED(argv);
     return STATUS_CMD_OK;
 }
 
-int builtin_false(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_false(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     UNUSED(parser);
     UNUSED(streams);
     UNUSED(argv);
     return STATUS_CMD_ERROR;
 }
 
-int builtin_gettext(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_gettext(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     UNUSED(parser);
     UNUSED(streams);
     for (int i = 1; i < builtin_count_args(argv); i++) {
@@ -459,8 +459,11 @@ proc_status_t builtin_run(parser_t &parser, wchar_t **argv, io_streams_t &stream
     }
 
     if (const builtin_data_t *data = builtin_lookup(argv[0])) {
-        int ret = data->func(parser, streams, argv);
-        return proc_status_t::from_exit_code(ret);
+        maybe_t<int> ret = data->func(parser, streams, argv);
+        if (!ret) {
+            return proc_status_t::empty();
+        }
+        return proc_status_t::from_exit_code(ret.value());
     }
 
     FLOGF(error, UNKNOWN_BUILTIN_ERR_MSG, argv[0]);
diff --git a/src/builtin.h b/src/builtin.h
index 1629c4a79..88e01769a 100644
--- a/src/builtin.h
+++ b/src/builtin.h
@@ -20,7 +20,7 @@ struct builtin_data_t {
     // Name of the builtin.
     const wchar_t *name;
     // Function pointer to the builtin implementation.
-    int (*func)(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+    maybe_t<int> (*func)(parser_t &parser, io_streams_t &streams, wchar_t **argv);
     // Description of what the builtin does.
     const wchar_t *desc;
 
diff --git a/src/builtin_argparse.cpp b/src/builtin_argparse.cpp
index bde552ef1..76f73dc3c 100644
--- a/src/builtin_argparse.cpp
+++ b/src/builtin_argparse.cpp
@@ -684,7 +684,7 @@ static void set_argparse_result_vars(env_stack_t &vars, const argparse_cmd_opts_
 /// an external command also means its output has to be in a form that can be eval'd. Because our
 /// version is a builtin it can directly set variables local to the current scope (e.g., a
 /// function). It doesn't need to write anything to stdout that then needs to be eval'd.
-int builtin_argparse(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_argparse(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     argparse_cmd_opts_t opts;
diff --git a/src/builtin_argparse.h b/src/builtin_argparse.h
index b515e0bce..24e4b6079 100644
--- a/src/builtin_argparse.h
+++ b/src/builtin_argparse.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_ARGPARSE_H
 #define FISH_BUILTIN_ARGPARSE_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_argparse(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_argparse(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_bg.cpp b/src/builtin_bg.cpp
index 64b0ec5c8..798d72511 100644
--- a/src/builtin_bg.cpp
+++ b/src/builtin_bg.cpp
@@ -37,7 +37,7 @@ static int send_to_bg(parser_t &parser, io_streams_t &streams, job_t *j) {
 }
 
 /// Builtin for putting a job in the background.
-int builtin_bg(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_bg(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_bg.h b/src/builtin_bg.h
index 3fcb3d0c0..bb628a433 100644
--- a/src/builtin_bg.h
+++ b/src/builtin_bg.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_BG_H
 #define FISH_BUILTIN_BG_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_bg(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_bg(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_bind.cpp b/src/builtin_bind.cpp
index 3c7c088e1..f497f8a68 100644
--- a/src/builtin_bind.cpp
+++ b/src/builtin_bind.cpp
@@ -413,7 +413,7 @@ int parse_cmd_opts(bind_cmd_opts_t &opts, int *optind,  //!OCLINT(high ncss meth
 }
 
 /// The bind builtin, used for setting character sequences.
-int builtin_bind_t::builtin_bind(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_bind_t::builtin_bind(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     bind_cmd_opts_t opts;
diff --git a/src/builtin_bind.h b/src/builtin_bind.h
index 769fea782..a6050f93e 100644
--- a/src/builtin_bind.h
+++ b/src/builtin_bind.h
@@ -11,7 +11,7 @@ struct bind_cmd_opts_t;
 
 class builtin_bind_t {
    public:
-    int builtin_bind(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+    maybe_t<int> builtin_bind(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 
     builtin_bind_t() : input_mappings_(input_mappings()) {}
 
@@ -38,7 +38,7 @@ class builtin_bind_t {
                   io_streams_t &streams);
 };
 
-inline int builtin_bind(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+inline maybe_t<int> builtin_bind(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     builtin_bind_t bind;
     return bind.builtin_bind(parser, streams, argv);
 }
diff --git a/src/builtin_block.cpp b/src/builtin_block.cpp
index fcf2dd3a2..e2e9b78d8 100644
--- a/src/builtin_block.cpp
+++ b/src/builtin_block.cpp
@@ -70,7 +70,7 @@ static int parse_cmd_opts(block_cmd_opts_t &opts, int *optind,  //!OCLINT(high n
 }
 
 /// The block builtin, used for temporarily blocking events.
-int builtin_block(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_block(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     block_cmd_opts_t opts;
diff --git a/src/builtin_block.h b/src/builtin_block.h
index 5399c4fa6..96cf844cf 100644
--- a/src/builtin_block.h
+++ b/src/builtin_block.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_BLOCK_H
 #define FISH_BUILTIN_BLOCK_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_block(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_block(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_builtin.cpp b/src/builtin_builtin.cpp
index 7e94ee2a1..30d291274 100644
--- a/src/builtin_builtin.cpp
+++ b/src/builtin_builtin.cpp
@@ -65,7 +65,7 @@ static int parse_cmd_opts(builtin_cmd_opts_t &opts, int *optind, int argc, wchar
 /// The builtin builtin, used for giving builtins precedence over functions. Mostly handled by the
 /// parser. All this code does is some additional operational modes, such as printing a list of all
 /// builtins, printing help, etc.
-int builtin_builtin(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_builtin(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     builtin_cmd_opts_t opts;
diff --git a/src/builtin_builtin.h b/src/builtin_builtin.h
index ac8493447..75e5ccc4c 100644
--- a/src/builtin_builtin.h
+++ b/src/builtin_builtin.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_BUILTIN_H
 #define FISH_BUILTIN_BUILTIN_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_builtin(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_builtin(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_cd.cpp b/src/builtin_cd.cpp
index 93d1bd204..a09c05edb 100644
--- a/src/builtin_cd.cpp
+++ b/src/builtin_cd.cpp
@@ -20,7 +20,7 @@
 
 /// The cd builtin. Changes the current directory to the one specified or to $HOME if none is
 /// specified. The directory can be relative to any directory in the CDPATH variable.
-int builtin_cd(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_cd(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_cd.h b/src/builtin_cd.h
index 85aa8cb28..a28a85f4c 100644
--- a/src/builtin_cd.h
+++ b/src/builtin_cd.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_CD_H
 #define FISH_BUILTIN_CD_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_cd(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_cd(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_command.cpp b/src/builtin_command.cpp
index 6de2347ac..462e33a84 100644
--- a/src/builtin_command.cpp
+++ b/src/builtin_command.cpp
@@ -73,7 +73,7 @@ static int parse_cmd_opts(command_cmd_opts_t &opts, int *optind, int argc, wchar
 
 /// Implementation of the builtin 'command'. Actual command running is handled by the parser, this
 /// just processes the flags.
-int builtin_command(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_command(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     command_cmd_opts_t opts;
diff --git a/src/builtin_command.h b/src/builtin_command.h
index 75f5fc1e6..8557bc13d 100644
--- a/src/builtin_command.h
+++ b/src/builtin_command.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_COMMAND_H
 #define FISH_BUILTIN_COMMAND_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_command(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_command(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_commandline.cpp b/src/builtin_commandline.cpp
index 1ee6fbc93..a4bcf9768 100644
--- a/src/builtin_commandline.cpp
+++ b/src/builtin_commandline.cpp
@@ -121,7 +121,7 @@ static void write_part(const wchar_t *begin, const wchar_t *end, int cut_at_curs
 }
 
 /// The commandline builtin. It is used for specifying a new value for the commandline.
-int builtin_commandline(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_commandline(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     // Pointer to what the commandline builtin considers to be the current contents of the command
     // line buffer.
     const wchar_t *current_buffer = nullptr;
diff --git a/src/builtin_commandline.h b/src/builtin_commandline.h
index 5237d240f..277056ae5 100644
--- a/src/builtin_commandline.h
+++ b/src/builtin_commandline.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-int builtin_commandline(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_commandline(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_complete.cpp b/src/builtin_complete.cpp
index 2d6f9552c..9d70ca550 100644
--- a/src/builtin_complete.cpp
+++ b/src/builtin_complete.cpp
@@ -110,7 +110,7 @@ static void builtin_complete_remove(const wcstring_list_t &cmds, const wcstring_
 
 /// The complete builtin. Used for specifying programmable tab-completions. Calls the functions in
 // complete.cpp for any heavy lifting.
-int builtin_complete(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_complete(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     ASSERT_IS_MAIN_THREAD();
 
     wchar_t *cmd = argv[0];
diff --git a/src/builtin_complete.h b/src/builtin_complete.h
index f69d98356..c2f3ab31b 100644
--- a/src/builtin_complete.h
+++ b/src/builtin_complete.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-int builtin_complete(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_complete(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_contains.cpp b/src/builtin_contains.cpp
index 91ddb3c14..389ad0916 100644
--- a/src/builtin_contains.cpp
+++ b/src/builtin_contains.cpp
@@ -58,7 +58,7 @@ static int parse_cmd_opts(contains_cmd_opts_t &opts, int *optind, int argc, wcha
 
 /// Implementation of the builtin contains command, used to check if a specified string is part of
 /// a list.
-int builtin_contains(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_contains(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     contains_cmd_opts_t opts;
diff --git a/src/builtin_contains.h b/src/builtin_contains.h
index f331846f1..fca65875c 100644
--- a/src/builtin_contains.h
+++ b/src/builtin_contains.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_CONTAINS_H
 #define FISH_BUILTIN_CONTAINS_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_contains(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_contains(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_disown.cpp b/src/builtin_disown.cpp
index 510044803..cfccefa7a 100644
--- a/src/builtin_disown.cpp
+++ b/src/builtin_disown.cpp
@@ -42,7 +42,7 @@ static int disown_job(const wchar_t *cmd, parser_t &parser, io_streams_t &stream
 }
 
 /// Builtin for removing jobs from the job list.
-int builtin_disown(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_disown(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_disown.h b/src/builtin_disown.h
index 4469880e1..d6c836928 100644
--- a/src/builtin_disown.h
+++ b/src/builtin_disown.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_DISOWN_H
 #define FISH_BUILTIN_DISOWN_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_disown(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_disown(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_echo.cpp b/src/builtin_echo.cpp
index bac2adf85..9d2c78e71 100644
--- a/src/builtin_echo.cpp
+++ b/src/builtin_echo.cpp
@@ -180,7 +180,7 @@ static bool builtin_echo_parse_numeric_sequence(const wchar_t *str, size_t *cons
 ///
 /// Bash only respects -n if it's the first argument. We'll do the same. We also support a new,
 /// fish specific, option -s to mean "no spaces".
-int builtin_echo(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_echo(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     UNUSED(cmd);
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_echo.h b/src/builtin_echo.h
index ecf133700..612e869a7 100644
--- a/src/builtin_echo.h
+++ b/src/builtin_echo.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_ECHO_H
 #define FISH_BUILTIN_ECHO_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_echo(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_echo(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_emit.cpp b/src/builtin_emit.cpp
index b837b30ab..161d652a0 100644
--- a/src/builtin_emit.cpp
+++ b/src/builtin_emit.cpp
@@ -11,7 +11,7 @@
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Implementation of the builtin emit command, used to create events.
-int builtin_emit(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_emit(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_emit.h b/src/builtin_emit.h
index 0bf500002..6ca671d88 100644
--- a/src/builtin_emit.h
+++ b/src/builtin_emit.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_EMIT_H
 #define FISH_BUILTIN_EMIT_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_emit(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_emit(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_eval.cpp b/src/builtin_eval.cpp
index e8da6c7c8..d095cf61b 100644
--- a/src/builtin_eval.cpp
+++ b/src/builtin_eval.cpp
@@ -15,7 +15,7 @@
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Implementation of eval builtin.
-int builtin_eval(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_eval(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     int argc = builtin_count_args(argv);
     if (argc <= 1) {
         return STATUS_CMD_OK;
diff --git a/src/builtin_eval.h b/src/builtin_eval.h
index 6cceaacc3..ae67c7da9 100644
--- a/src/builtin_eval.h
+++ b/src/builtin_eval.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_EVAL_H
 #define FISH_BUILTIN_EVAL_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_eval(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_eval(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_exit.cpp b/src/builtin_exit.cpp
index 8073dee53..51e2dffc4 100644
--- a/src/builtin_exit.cpp
+++ b/src/builtin_exit.cpp
@@ -58,7 +58,7 @@ static int parse_cmd_opts(exit_cmd_opts_t &opts, int *optind,  //!OCLINT(high nc
 }
 
 /// The exit builtin. Calls reader_exit to exit and returns the value specified.
-int builtin_exit(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_exit(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     exit_cmd_opts_t opts;
diff --git a/src/builtin_exit.h b/src/builtin_exit.h
index 1a279ab5f..f446daddf 100644
--- a/src/builtin_exit.h
+++ b/src/builtin_exit.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_EXIT_H
 #define FISH_BUILTIN_EXIT_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_exit(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_exit(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_fg.cpp b/src/builtin_fg.cpp
index 7bc05f467..1211c27c1 100644
--- a/src/builtin_fg.cpp
+++ b/src/builtin_fg.cpp
@@ -21,7 +21,7 @@
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Builtin for putting a job in the foreground.
-int builtin_fg(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_fg(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_fg.h b/src/builtin_fg.h
index 251ce157b..8503f7286 100644
--- a/src/builtin_fg.h
+++ b/src/builtin_fg.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_FG_H
 #define FISH_BUILTIN_FG_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_fg(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_fg(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_function.cpp b/src/builtin_function.cpp
index 5300b3e07..ef7c329ae 100644
--- a/src/builtin_function.cpp
+++ b/src/builtin_function.cpp
@@ -199,7 +199,7 @@ static int validate_function_name(int argc, const wchar_t *const *argv, wcstring
 
 /// Define a function. Calls into `function.cpp` to perform the heavy lifting of defining a
 /// function.
-int builtin_function(parser_t &parser, io_streams_t &streams, const wcstring_list_t &c_args,
+maybe_t<int> builtin_function(parser_t &parser, io_streams_t &streams, const wcstring_list_t &c_args,
                      const parsed_source_ref_t &source, const ast::block_statement_t &func_node) {
     assert(source && "Missing source in builtin_function");
     // The wgetopt function expects 'function' as the first argument. Make a new wcstring_list with
diff --git a/src/builtin_function.h b/src/builtin_function.h
index 4da1a378c..e9aae2183 100644
--- a/src/builtin_function.h
+++ b/src/builtin_function.h
@@ -12,6 +12,6 @@ namespace ast {
 struct block_statement_t;
 }
 
-int builtin_function(parser_t &parser, io_streams_t &streams, const wcstring_list_t &c_args,
+maybe_t<int> builtin_function(parser_t &parser, io_streams_t &streams, const wcstring_list_t &c_args,
                      const parsed_source_ref_t &source, const ast::block_statement_t &func_node);
 #endif
diff --git a/src/builtin_functions.cpp b/src/builtin_functions.cpp
index 7cf37d9c1..7e08a5415 100644
--- a/src/builtin_functions.cpp
+++ b/src/builtin_functions.cpp
@@ -282,7 +282,7 @@ static int report_function_metadata(const wchar_t *funcname, bool verbose, io_st
 }
 
 /// The functions builtin, used for listing and erasing functions.
-int builtin_functions(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_functions(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     functions_cmd_opts_t opts;
diff --git a/src/builtin_functions.h b/src/builtin_functions.h
index c7d4b3d6f..1746eaac3 100644
--- a/src/builtin_functions.h
+++ b/src/builtin_functions.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_FUNCTIONS_H
 #define FISH_BUILTIN_FUNCTIONS_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_functions(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_functions(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_history.cpp b/src/builtin_history.cpp
index 0009f58d2..61716a77f 100644
--- a/src/builtin_history.cpp
+++ b/src/builtin_history.cpp
@@ -200,7 +200,7 @@ static int parse_cmd_opts(history_cmd_opts_t &opts, int *optind,  //!OCLINT(high
 }
 
 /// Manipulate history of interactive commands executed by the user.
-int builtin_history(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_history(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     history_cmd_opts_t opts;
diff --git a/src/builtin_history.h b/src/builtin_history.h
index 7c27ed932..3aef6aacd 100644
--- a/src/builtin_history.h
+++ b/src/builtin_history.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_HISTORY_H
 #define FISH_BUILTIN_HISTORY_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_history(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_history(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_jobs.cpp b/src/builtin_jobs.cpp
index 9ac98c1bd..8248c3c5f 100644
--- a/src/builtin_jobs.cpp
+++ b/src/builtin_jobs.cpp
@@ -121,7 +121,7 @@ static void builtin_jobs_print(const job_t *j, int mode, int header, io_streams_
 }
 
 /// The jobs builtin. Used for printing running jobs. Defined in builtin_jobs.c.
-int builtin_jobs(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_jobs(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     bool found = false;
diff --git a/src/builtin_jobs.h b/src/builtin_jobs.h
index adb3cfba0..a92375573 100644
--- a/src/builtin_jobs.h
+++ b/src/builtin_jobs.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-int builtin_jobs(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_jobs(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_math.cpp b/src/builtin_math.cpp
index ac0caee6b..84111fb39 100644
--- a/src/builtin_math.cpp
+++ b/src/builtin_math.cpp
@@ -232,7 +232,7 @@ static int evaluate_expression(const wchar_t *cmd, const parser_t &parser, io_st
 }
 
 /// The math builtin evaluates math expressions.
-int builtin_math(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_math(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     math_cmd_opts_t opts;
diff --git a/src/builtin_math.h b/src/builtin_math.h
index 76d5a5da8..80ef56702 100644
--- a/src/builtin_math.h
+++ b/src/builtin_math.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_MATH_H
 #define FISH_BUILTIN_MATH_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_math(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_math(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_printf.cpp b/src/builtin_printf.cpp
index 834fbc178..61cef9fcd 100644
--- a/src/builtin_printf.cpp
+++ b/src/builtin_printf.cpp
@@ -737,7 +737,7 @@ int builtin_printf_state_t::print_formatted(const wchar_t *format, int argc, wch
 }
 
 /// The printf builtin.
-int builtin_printf(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_printf(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_printf.h b/src/builtin_printf.h
index 4248d9785..08be3e076 100644
--- a/src/builtin_printf.h
+++ b/src/builtin_printf.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-int builtin_printf(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_printf(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_pwd.cpp b/src/builtin_pwd.cpp
index e3619881f..907a04fdf 100644
--- a/src/builtin_pwd.cpp
+++ b/src/builtin_pwd.cpp
@@ -19,7 +19,7 @@ static const struct woption long_options[] = {{L"help", no_argument, nullptr, 'h
                                               {L"logical", no_argument, nullptr, 'L'},
                                               {L"physical", no_argument, nullptr, 'P'},
                                               {nullptr, 0, nullptr, 0}};
-int builtin_pwd(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_pwd(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     UNUSED(parser);
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_pwd.h b/src/builtin_pwd.h
index 431a52ff5..5e7b392fa 100644
--- a/src/builtin_pwd.h
+++ b/src/builtin_pwd.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_PWD_H
 #define FISH_BUILTIN_PWD_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_pwd(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_pwd(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_random.cpp b/src/builtin_random.cpp
index 46771c766..88e4c431a 100644
--- a/src/builtin_random.cpp
+++ b/src/builtin_random.cpp
@@ -27,7 +27,7 @@ static std::minstd_rand get_seeded_engine() {
 }
 
 /// The random builtin generates random numbers.
-int builtin_random(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_random(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     help_only_cmd_opts_t opts;
diff --git a/src/builtin_random.h b/src/builtin_random.h
index 878c73f25..80fd5b3f7 100644
--- a/src/builtin_random.h
+++ b/src/builtin_random.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_RANDOM_H
 #define FISH_BUILTIN_RANDOM_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_random(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_random(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_read.cpp b/src/builtin_read.cpp
index b8df208b1..ed6853375 100644
--- a/src/builtin_read.cpp
+++ b/src/builtin_read.cpp
@@ -431,7 +431,7 @@ static int validate_read_args(const wchar_t *cmd, read_cmd_opts_t &opts, int arg
 }
 
 /// The read builtin. Reads from stdin and stores the values in environment variables.
-int builtin_read(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_read(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     wcstring buff;
diff --git a/src/builtin_read.h b/src/builtin_read.h
index c65fe5bfa..f1fdccdee 100644
--- a/src/builtin_read.h
+++ b/src/builtin_read.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_READ_H
 #define FISH_BUILTIN_READ_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_read(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_read(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_realpath.cpp b/src/builtin_realpath.cpp
index 09858ee9d..1264545c8 100644
--- a/src/builtin_realpath.cpp
+++ b/src/builtin_realpath.cpp
@@ -17,7 +17,7 @@
 /// An implementation of the external realpath command. Doesn't support any options.
 /// In general scripts shouldn't invoke this directly. They should just use `realpath` which
 /// will fallback to this builtin if an external command cannot be found.
-int builtin_realpath(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_realpath(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     help_only_cmd_opts_t opts;
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_realpath.h b/src/builtin_realpath.h
index 1fa7d16ad..2022e9d29 100644
--- a/src/builtin_realpath.h
+++ b/src/builtin_realpath.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_REALPATH_H
 #define FISH_BUILTIN_REALPATH_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_realpath(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_realpath(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_return.cpp b/src/builtin_return.cpp
index 8c0fb302b..2c384b23b 100644
--- a/src/builtin_return.cpp
+++ b/src/builtin_return.cpp
@@ -57,7 +57,7 @@ static int parse_cmd_opts(return_cmd_opts_t &opts, int *optind,  //!OCLINT(high
 }
 
 /// Function for handling the return builtin.
-int builtin_return(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_return(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     return_cmd_opts_t opts;
diff --git a/src/builtin_return.h b/src/builtin_return.h
index 81a3e4736..401ed6ec0 100644
--- a/src/builtin_return.h
+++ b/src/builtin_return.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_RETURN_H
 #define FISH_BUILTIN_RETURN_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_return(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_return(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_set.cpp b/src/builtin_set.cpp
index 5b30cc43a..06d04852e 100644
--- a/src/builtin_set.cpp
+++ b/src/builtin_set.cpp
@@ -804,7 +804,7 @@ static int builtin_set_set(const wchar_t *cmd, set_cmd_opts_t &opts, int argc, w
 }
 
 /// The set builtin creates, updates, and erases (removes, deletes) variables.
-int builtin_set(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_set(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     const int incoming_exit_status = parser.get_last_status();
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_set.h b/src/builtin_set.h
index ffd517da3..04c4877cd 100644
--- a/src/builtin_set.h
+++ b/src/builtin_set.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-int builtin_set(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_set(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_set_color.cpp b/src/builtin_set_color.cpp
index 7320dfdcc..5d6ee22d1 100644
--- a/src/builtin_set_color.cpp
+++ b/src/builtin_set_color.cpp
@@ -67,7 +67,7 @@ static char dim_esc[] = "\x1B[2m";
 #endif
 
 /// set_color builtin.
-int builtin_set_color(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_set_color(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     // By the time this is called we should have initialized the curses subsystem.
     assert(curses_initialized);
 
diff --git a/src/builtin_set_color.h b/src/builtin_set_color.h
index 87ae3e37f..06be7db91 100644
--- a/src/builtin_set_color.h
+++ b/src/builtin_set_color.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-int builtin_set_color(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_set_color(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_source.cpp b/src/builtin_source.cpp
index 633487e90..be3ada8e7 100644
--- a/src/builtin_source.cpp
+++ b/src/builtin_source.cpp
@@ -22,7 +22,7 @@
 
 /// The  source builtin, sometimes called `.`. Evaluates the contents of a file in the current
 /// context.
-int builtin_source(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_source(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     ASSERT_IS_MAIN_THREAD();
     const wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
diff --git a/src/builtin_source.h b/src/builtin_source.h
index 4aaf1259e..e292727da 100644
--- a/src/builtin_source.h
+++ b/src/builtin_source.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_SOURCE_H
 #define FISH_BUILTIN_SOURCE_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_source(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_source(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_status.cpp b/src/builtin_status.cpp
index 8b2cee5e3..58fbe9230 100644
--- a/src/builtin_status.cpp
+++ b/src/builtin_status.cpp
@@ -274,7 +274,7 @@ static int parse_cmd_opts(status_cmd_opts_t &opts, int *optind,  //!OCLINT(high
 }
 
 /// The status builtin. Gives various status information on fish.
-int builtin_status(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_status(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     status_cmd_opts_t opts;
diff --git a/src/builtin_status.h b/src/builtin_status.h
index bf5eea440..01855e120 100644
--- a/src/builtin_status.h
+++ b/src/builtin_status.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_STATUS_H
 #define FISH_BUILTIN_STATUS_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_status(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_status(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_string.cpp b/src/builtin_string.cpp
index e4b3c9a44..429676f79 100644
--- a/src/builtin_string.cpp
+++ b/src/builtin_string.cpp
@@ -1451,7 +1451,7 @@ string_subcommands[] = {
     {nullptr, nullptr}};
 
 /// The string builtin, for manipulating strings.
-int builtin_string(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     if (argc <= 1) {
diff --git a/src/builtin_string.h b/src/builtin_string.h
index ce139a6f0..47c5e1227 100644
--- a/src/builtin_string.h
+++ b/src/builtin_string.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-int builtin_string(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_test.cpp b/src/builtin_test.cpp
index b6851ebf5..717e9817f 100644
--- a/src/builtin_test.cpp
+++ b/src/builtin_test.cpp
@@ -845,7 +845,7 @@ static bool unary_primary_evaluate(test_expressions::token_t token, const wcstri
 /// supports a more limited range of functionality.
 ///
 /// Return status is the final shell status, i.e. 0 for true, 1 for false and 2 for error.
-int builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     UNUSED(parser);
     using namespace test_expressions;
 
diff --git a/src/builtin_test.h b/src/builtin_test.h
index b350cc639..8b8935e86 100644
--- a/src/builtin_test.h
+++ b/src/builtin_test.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_TEST_H
 #define FISH_BUILTIN_TEST_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_ulimit.cpp b/src/builtin_ulimit.cpp
index df9621538..72b114cfe 100644
--- a/src/builtin_ulimit.cpp
+++ b/src/builtin_ulimit.cpp
@@ -149,7 +149,7 @@ static int set_limit(int resource, int hard, int soft, rlim_t value, io_streams_
 }
 
 /// The ulimit builtin, used for setting resource limits.
-int builtin_ulimit(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_ulimit(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
     int argc = builtin_count_args(argv);
     bool report_all = false;
diff --git a/src/builtin_ulimit.h b/src/builtin_ulimit.h
index 19c9348e5..1d64c39e4 100644
--- a/src/builtin_ulimit.h
+++ b/src/builtin_ulimit.h
@@ -7,5 +7,5 @@
 
 class parser_t;
 
-int builtin_ulimit(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_ulimit(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/builtin_wait.cpp b/src/builtin_wait.cpp
index 06dc575d8..0d60c42a4 100644
--- a/src/builtin_wait.cpp
+++ b/src/builtin_wait.cpp
@@ -172,7 +172,7 @@ static bool find_job_by_name(const wchar_t *proc, std::vector<job_id_t> &ids,
 
 /// The following function is invoked on the main thread, because the job operation is not thread
 /// safe. It waits for child jobs, not for child processes individually.
-int builtin_wait(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
+maybe_t<int> builtin_wait(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     ASSERT_IS_MAIN_THREAD();
     int retval = STATUS_CMD_OK;
     const wchar_t *cmd = argv[0];
diff --git a/src/builtin_wait.h b/src/builtin_wait.h
index d0444c34b..a9945325b 100644
--- a/src/builtin_wait.h
+++ b/src/builtin_wait.h
@@ -2,8 +2,10 @@
 #ifndef FISH_BUILTIN_WAIT_H
 #define FISH_BUILTIN_WAIT_H
 
+#include "maybe.h"
+
 class parser_t;
 struct io_streams_t;
 
-int builtin_wait(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_wait(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 #endif
diff --git a/src/exec.cpp b/src/exec.cpp
index be05303d0..0202fa64c 100644
--- a/src/exec.cpp
+++ b/src/exec.cpp
@@ -289,7 +289,11 @@ static void run_internal_process_or_short_circuit(parser_t &parser, const std::s
         if (p->is_last_in_job) {
             FLOGF(exec_job_status, L"Set status of job %d (%ls) to %d using short circuit",
                   j->job_id(), j->preview().c_str(), p->status);
-            parser.set_last_statuses(j->get_statuses());
+            auto statuses = j->get_statuses();
+            if (statuses) {
+                parser.set_last_statuses(statuses.value());
+                parser.libdata().status_count++;
+            }
         }
     } else {
         run_internal_process(p, std::move(outdata), std::move(errdata), ios);
diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index 8ea642865..0f1b58293 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -2519,7 +2519,7 @@ static void test_is_potential_path() {
 }
 
 /// Test the 'test' builtin.
-int builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_test(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 static bool run_one_test_test(int expected, wcstring_list_t &lst, bool bracket) {
     parser_t &parser = parser_t::principal_parser();
     size_t i, count = lst.size();
@@ -2535,13 +2535,16 @@ static bool run_one_test_test(int expected, wcstring_list_t &lst, bool bracket)
     argv[i + 1] = NULL;
     null_output_stream_t null{};
     io_streams_t streams(null, null);
-    int result = builtin_test(parser, streams, argv);
+    maybe_t<int> result = builtin_test(parser, streams, argv);
 
-    if (expected != result) err(L"expected builtin_test() to return %d, got %d", expected, result);
+    if (result != expected) {
+        std::wstring got = result ? std::to_wstring(result.value()) : L"nothing";
+        err(L"expected builtin_test() to return %d, got %s", expected, got.c_str());
+    }
 
     delete[] argv;
 
-    return expected == result;
+    return result == expected;
 }
 
 static bool run_test_test(int expected, const wcstring &str) {
@@ -5098,7 +5101,7 @@ static void test_pcre2_escape() {
     }
 }
 
-int builtin_string(parser_t &parser, io_streams_t &streams, wchar_t **argv);
+maybe_t<int> builtin_string(parser_t &parser, io_streams_t &streams, wchar_t **argv);
 static void run_one_string_test(const wchar_t *const *argv, int expected_rc,
                                 const wchar_t *expected_out) {
     parser_t &parser = parser_t::principal_parser();
@@ -5106,15 +5109,16 @@ static void run_one_string_test(const wchar_t *const *argv, int expected_rc,
     null_output_stream_t errs{};
     io_streams_t streams(outs, errs);
     streams.stdin_is_directly_redirected = false;  // read from argv instead of stdin
-    int rc = builtin_string(parser, streams, const_cast<wchar_t **>(argv));
+    maybe_t<int> rc = builtin_string(parser, streams, const_cast<wchar_t **>(argv));
     wcstring args;
     for (int i = 0; argv[i] != NULL; i++) {
         args += escape_string(argv[i], ESCAPE_ALL) + L' ';
     }
     args.resize(args.size() - 1);
     if (rc != expected_rc) {
-        err(L"Test failed on line %lu: [%ls]: expected return code %d but got %d", __LINE__,
-            args.c_str(), expected_rc, rc);
+        std::wstring got = rc ? std::to_wstring(rc.value()) : L"nothing";
+        err(L"Test failed on line %lu: [%ls]: expected return code %d but got %s", __LINE__,
+            args.c_str(), expected_rc, got.c_str());
     } else if (outs.contents() != expected_out) {
         err(L"Test failed on line %lu: [%ls]: expected [%ls] but got [%ls]", __LINE__, args.c_str(),
             escape_string(expected_out, ESCAPE_ALL).c_str(),
diff --git a/src/maybe.h b/src/maybe.h
index 4f0a78800..42fe8ac3e 100644
--- a/src/maybe.h
+++ b/src/maybe.h
@@ -3,6 +3,7 @@
 
 #include <cassert>
 #include <type_traits>
+#include <utility>
 
 namespace maybe_detail {
 // Template magic to make maybe_t<T> copyable iff T is copyable.
diff --git a/src/parse_execution.cpp b/src/parse_execution.cpp
index eee1fc14e..ca62ed52d 100644
--- a/src/parse_execution.cpp
+++ b/src/parse_execution.cpp
@@ -392,13 +392,17 @@ end_execution_reason_t parse_execution_context_t::run_function_statement(
     buffered_output_stream_t outs(0);
     buffered_output_stream_t errs(0);
     io_streams_t streams(outs, errs);
-    int err = builtin_function(*parser, streams, arguments, pstree, statement);
-    parser->libdata().status_count++;
-    parser->set_last_statuses(statuses_t::just(err));
+    int err_code = 0;
+    maybe_t<int> err = builtin_function(*parser, streams, arguments, pstree, statement);
+    if (err) {
+        err_code = err.value();
+        parser->libdata().status_count++;
+        parser->set_last_statuses(statuses_t::just(err_code));
+    }
 
     wcstring errtext = errs.contents();
     if (!errtext.empty()) {
-        return this->report_error(err, header, L"%ls", errtext.c_str());
+        return this->report_error(err_code, header, L"%ls", errtext.c_str());
     }
     return result;
 }
diff --git a/src/proc.cpp b/src/proc.cpp
index 150f0dddd..06e46b511 100644
--- a/src/proc.cpp
+++ b/src/proc.cpp
@@ -167,17 +167,30 @@ bool job_t::signal(int signal) {
     return true;
 }
 
-statuses_t job_t::get_statuses() const {
+maybe_t<statuses_t> job_t::get_statuses() const {
     statuses_t st{};
+    bool has_status = false;
+    int laststatus = 0;
     st.pipestatus.reserve(processes.size());
     for (const auto &p : processes) {
         auto status = p->status;
+        if (status.is_empty()) {
+            // Corner case for if a variable assignment is part of a pipeline.
+            // e.g. `false | set foo bar | true` will push 1 in the second spot,
+            // for a complete pipestatus of `1 1 0`.
+            st.pipestatus.push_back(laststatus);
+            continue;
+        }
         if (status.signal_exited()) {
             st.kill_signal = status.signal_code();
         }
+        laststatus = status.status_value();
+        has_status = true;
         st.pipestatus.push_back(status.status_value());
     }
-    int laststatus = st.pipestatus.back();
+    if (!has_status) {
+        return none();
+    }
     st.status = flags().negate ? !laststatus : laststatus;
     return st;
 }
@@ -997,8 +1010,11 @@ void job_t::continue_job(parser_t &parser, bool in_foreground) {
         // finished.
         const auto &p = processes.back();
         if (p->status.normal_exited() || p->status.signal_exited()) {
-            parser.set_last_statuses(get_statuses());
-            parser.libdata().status_count++;
+            auto statuses = get_statuses();
+            if (statuses) {
+                parser.set_last_statuses(statuses.value());
+                parser.libdata().status_count++;
+            }
         }
     }
 }
diff --git a/src/proc.h b/src/proc.h
index 2700d4610..deb36a7c7 100644
--- a/src/proc.h
+++ b/src/proc.h
@@ -54,7 +54,12 @@ using job_group_ref_t = std::shared_ptr<job_group_t>;
 class proc_status_t {
     int status_{};
 
-    explicit proc_status_t(int status) : status_(status) {}
+    /// If set, there is no actual status to report, e.g. background or variable assignment.
+    bool empty_{};
+
+    explicit proc_status_t(int status) : status_(status), empty_(false) {}
+
+    proc_status_t(int status, bool empty) : status_(status), empty_(empty) {}
 
     /// Encode a return value \p ret and signal \p sig into a status value like waitpid() does.
     static constexpr int w_exitcode(int ret, int sig) {
@@ -84,6 +89,12 @@ class proc_status_t {
         return proc_status_t(w_exitcode(0 /* ret */, sig));
     }
 
+    /// Construct an empty status_t (e.g. `set foo bar`).
+    static proc_status_t empty() {
+        bool empty = true;
+        return proc_status_t(0, empty);
+    }
+
     /// \return if we are stopped (as in SIGSTOP).
     bool stopped() const { return WIFSTOPPED(status_); }
 
@@ -111,6 +122,9 @@ class proc_status_t {
     /// \return if this status represents success.
     bool is_success() const { return normal_exited() && exit_code() == EXIT_SUCCESS; }
 
+    /// \return if this status is empty.
+    bool is_empty() const { return empty_; }
+
     /// \return the value appropriate to populate $status.
     int status_value() const {
         if (signal_exited()) {
@@ -465,7 +479,7 @@ class job_t {
     bool signal(int signal);
 
     /// \returns the statuses for this job.
-    statuses_t get_statuses() const;
+    maybe_t<statuses_t> get_statuses() const;
 };
 
 /// Whether this shell is attached to the keyboard at all.