Revert "I need to take a break. Fixup."

This reverts commit 3e556b984c7769a25b301871bc788daecb6d6d4e.

Revert "Further fix the issue and add the assert that'd have prevented it."

This reverts commit 056502001eb94f1fc001126738055f6605a6fc21.

Revert "Fix actual issue with allow_use_posix_spawn."

This reverts commit 85b9f3c71f703429e44290b76e6d9e87b58d31ce.

Revert "Stop using posix_spawn when it is not allowed"

This reverts commit 9c896e199080bd4e219507961975a0ac97ebc32d.

Revert "don't even set up a fish_use_posix_spawn handler if unsupported"

This reverts commit 8b14ac4a9c3d0e15f9a7bd16a7633a9d1452b6d9.

src/env.h

@@ -298,6 +298,8 @@ class env_stack_t final : public environment_t {
     static env_stack_t &globals();
 };
 
+bool get_use_posix_spawn();
+
 extern bool term_has_xn;  // does the terminal have the "eat_newline_glitch"
 
 /// Returns true if we think the terminal supports setting its title.

src/env_dispatch.cpp

@@ -43,7 +43,6 @@
 #include "input_common.h"
 #include "maybe.h"
 #include "output.h"
-#include "postfork.h"
 #include "proc.h"
 #include "reader.h"
 #include "screen.h"
@@ -251,8 +250,16 @@ static void handle_curses_change(const environment_t &vars) {
     init_curses(vars);
 }
 
-static constexpr bool allow_use_posix_spawn() {
-#if defined(FISH_USE_POSIX_SPAWN)
+/// Whether to use posix_spawn when possible.
+static relaxed_atomic_bool_t g_use_posix_spawn{false};
+
+bool get_use_posix_spawn() { return g_use_posix_spawn; }
+
+extern "C" {
+const char *gnu_get_libc_version();
+}
+
+static bool allow_use_posix_spawn() {
     // OpenBSD's posix_spawn returns status 127, instead of erroring with ENOEXEC, when faced with a
     // shebangless script. Disable posix_spawn on OpenBSD.
 #if defined(__OpenBSD__)
@@ -264,21 +271,14 @@ static constexpr bool allow_use_posix_spawn() {
 #else                                             // !defined(__OpenBSD__)
     return true;
 #endif
-#else  // !defined(FISH_USE_POSIX_SPAWN)
-    return false;
-#endif
+    return true;
 }
 
-static relaxed_atomic_bool_t g_use_posix_spawn{false};
-bool get_use_posix_spawn() {
-    assert(allow_use_posix_spawn() && g_use_posix_spawn && "get_use_posix_spawn() called but not allowed");
-    return g_use_posix_spawn;
-}
-
-/// Whether to use posix_spawn when possible.
 static void handle_fish_use_posix_spawn_change(const environment_t &vars) {
-    // If the variable is missing or empty, we default to true if allowed.
-    if (auto var = vars.get(L"fish_use_posix_spawn")) {
+    // Note if the variable is missing or empty, we default to true if allowed.
+    if (!allow_use_posix_spawn()) {
+        g_use_posix_spawn = false;
+    } else if (auto var = vars.get(L"fish_use_posix_spawn")) {
         g_use_posix_spawn = var->empty() || bool_from_string(var->as_string());
     } else {
         g_use_posix_spawn = true;
@@ -331,9 +331,7 @@ static std::unique_ptr<const var_dispatch_table_t> create_dispatch_table() {
     var_dispatch_table->add(L"fish_history", handle_fish_history_change);
     var_dispatch_table->add(L"fish_autosuggestion_enabled", handle_autosuggestion_change);
     var_dispatch_table->add(L"TZ", handle_tz_change);
-    if (allow_use_posix_spawn()) {
-        var_dispatch_table->add(L"fish_use_posix_spawn", handle_fish_use_posix_spawn_change);
-    }
+    var_dispatch_table->add(L"fish_use_posix_spawn", handle_fish_use_posix_spawn_change);
     var_dispatch_table->add(L"fish_trace", handle_fish_trace);
     var_dispatch_table->add(L"fish_cursor_selection_mode",
                             handle_fish_cursor_selection_mode_change);
@@ -358,7 +356,7 @@ static void run_inits(const environment_t &vars) {
     guess_emoji_width(vars);
     update_wait_on_escape_ms(vars);
     handle_read_limit_change(vars);
-    if (allow_use_posix_spawn()) handle_fish_use_posix_spawn_change(vars);
+    handle_fish_use_posix_spawn_change(vars);
     handle_fish_trace(vars);
 }
 

src/env_dispatch.h

@@ -15,7 +15,4 @@ void env_dispatch_init(const environment_t &vars);
 /// React to changes in variables like LANG which require running some code.
 void env_dispatch_var_change(const wcstring &key, env_stack_t &vars);
 
-/// Whether posix_spawn is configured and/or allowed to be in use globally.
-bool get_use_posix_spawn();
-
 #endif

src/exec.cpp

@@ -30,7 +30,6 @@
 #include "builtin.h"
 #include "common.h"
 #include "env.h"
-#include "env_dispatch.h"
 #include "exec.h"
 #include "fallback.h"  // IWYU pragma: keep
 #include "fds.h"