Harmonize temporary Midnight Commander workarounds a bit

(cherry picked from commit 86a0a348ee)

src/env_dispatch.rs

@@ -452,6 +452,8 @@ fn update_fish_color_support(vars: &EnvStack) {
     crate::terminal::set_color_support(color_support);
 }
 
+pub const MIDNIGHT_COMMANDER_SID: &wstr = L!("MC_SID");
+
 // Initialize the terminal subsystem
 fn init_terminal(vars: &EnvStack) {
     let term = vars.get(L!("TERM"));
@@ -464,7 +466,7 @@ fn init_terminal(vars: &EnvStack) {
     IS_DUMB.store(term == "dumb");
     ONLY_GRAYSCALE.store(term == "ansi-m" || term == "linux-m" || term == "xterm-mono");
 
-    if vars.get(L!("MC_SID")).is_some() {
+    if vars.get(MIDNIGHT_COMMANDER_SID).is_some() {
         screen_set_midnight_commander_hack();
     }
 

src/reader.rs

@@ -66,6 +66,7 @@
 use crate::env::EnvStack;
 use crate::env::{EnvMode, Environment, Statuses};
 use crate::env_dispatch::guess_emoji_width;
+use crate::env_dispatch::MIDNIGHT_COMMANDER_SID;
 use crate::exec::exec_subshell;
 use crate::expand::expand_one;
 use crate::expand::{expand_string, expand_tilde, ExpandFlags, ExpandResultCode};
@@ -260,9 +261,9 @@ fn redirect_tty_after_sighup() {
     }
 }
 
-fn querying_allowed() -> bool {
+fn querying_allowed(vars: &dyn Environment) -> bool {
     future_feature_flags::test(FeatureFlag::query_term) &&
-    !is_dumb() && std::env::var_os("MC_TMPDIR").is_none()
+    !is_dumb() && vars.get(MIDNIGHT_COMMANDER_SID).is_none()
         // Could use /dev/tty in future.
         && isatty(STDOUT_FILENO)
 }
@@ -281,7 +282,7 @@ pub fn terminal_init(vars: &dyn Environment, inputfd: RawFd) -> InputEventQueue
         initialize_tty_protocols();
     });
 
-    if !querying_allowed() {
+    if !querying_allowed(vars) {
         return input_queue;
     }
 
@@ -1644,7 +1645,7 @@ pub fn combine_command_and_autosuggestion(
 
 impl<'a> Reader<'a> {
     pub fn request_cursor_position(&mut self, out: &mut Outputter, q: CursorPositionQuery) {
-        if !querying_allowed() {
+        if !querying_allowed(self.vars()) {
             return;
         }
         let mut query = self.blocking_query();

tests/test_driver.py

@@ -61,7 +61,6 @@ def makeenv(script_path: Path, home: Path) -> Dict[str, str]:
         "XDG_DATA_DIRS",
         "LANGUAGE",
         "MC_SID",
-        "MC_TMPDIR",
         "COLORTERM",
         "KONSOLE_VERSION",
         "STY",