refactor(auth): read the environment through the funnel

`mergify-auth` landed while this stack was in flight and its
production side already reads through `mergify_core::env`, since
`var_non_empty` predates the funnel. Only its tests were left:
`machine`'s `COMPUTERNAME` / `HOSTNAME` chain, `browser`'s
`SSH_CONNECTION` / `DISPLAY` / `WAYLAND_DISPLAY` probes, and
`with_mergify_token`.

They install an overlay now, like everywhere else, so the crate
stops mutating the process environment and drops its `temp-env`
dependency. `with_mergify_token` keeps its shape: the overlay is on
this thread and the `current_thread` runtime it builds drives the
future on that same thread, so the closure form still works and no
call site changes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Change-Id: I7d4c755cee8cc90db511ea671e5c23215300c03c

Author: sileht

Cargo.lock

@@ -25,7 +25,6 @@ url = { workspace = true }
 mergify-core = { path = "../mergify-core", features = ["test-support"] }
 mergify-test-support = { path = "../mergify-test-support" }
 serde_json = { workspace = true }
-temp-env = { workspace = true }
 tempfile = { workspace = true }
 tokio = { workspace = true, features = ["rt-multi-thread"] }
 wiremock = { workspace = true }

crates/mergify-auth/Cargo.toml

@@ -231,7 +231,7 @@ mod tests {
     #[cfg(target_os = "macos")]
     #[test]
     fn macos_opens_the_url_with_open() {
-        let command = temp_env::with_vars(
+        let command = mergify_core::env::testing::with_vars(
             [("SSH_CONNECTION", None::<&str>), ("SSH_TTY", None::<&str>)],
             || command_for("https://dashboard.mergify.com/device"),
         )
@@ -246,7 +246,7 @@ mod tests {
     #[cfg(all(unix, not(target_os = "macos")))]
     #[test]
     fn a_graphical_session_gets_xdg_open() {
-        let command = temp_env::with_vars(
+        let command = mergify_core::env::testing::with_vars(
             [("DISPLAY", Some(":0")), ("WAYLAND_DISPLAY", None::<&str>)],
             || command_for("https://dashboard.mergify.com/device"),
         )
@@ -263,7 +263,7 @@ mod tests {
     #[cfg(target_os = "macos")]
     #[test]
     fn an_ssh_session_to_a_mac_opens_nothing() {
-        let opened = temp_env::with_vars(
+        let opened = mergify_core::env::testing::with_vars(
             [
                 ("SSH_CONNECTION", Some("10.0.0.1 52000 10.0.0.2 22")),
                 ("SSH_TTY", None),
@@ -281,7 +281,7 @@ mod tests {
     #[cfg(all(unix, not(target_os = "macos")))]
     #[test]
     fn a_headless_session_opens_nothing() {
-        let opened = temp_env::with_vars(
+        let opened = mergify_core::env::testing::with_vars(
             [("DISPLAY", None::<&str>), ("WAYLAND_DISPLAY", None::<&str>)],
             || command_for("https://dashboard.mergify.com/device").is_ok(),
         );

crates/mergify-auth/src/browser.rs

@@ -41,17 +41,18 @@ mod testing {
     /// Run `body` to completion with `MERGIFY_TOKEN` forced to
     /// `value`.
     ///
-    /// `temp_env` cannot wrap an `.await`, so the future is driven
-    /// inside the closure instead. Without this the wiring that
-    /// reads the variable is untestable, and untestable wiring is
-    /// wiring a future edit can delete with the suite still green:
-    /// asserting on the renderer alone proves only that the renderer
-    /// can print a note, never that anything asks it to.
+    /// The overlay is installed on this thread and the future is
+    /// driven on it, by a `current_thread` runtime built here.
+    /// Without this the wiring that reads the variable is
+    /// untestable, and untestable wiring is wiring a future edit can
+    /// delete with the suite still green: asserting on the renderer
+    /// alone proves only that the renderer can print a note, never
+    /// that anything asks it to.
     pub fn with_mergify_token<F: std::future::Future>(value: Option<&str>, body: F) -> F::Output {
         let runtime = tokio::runtime::Builder::new_current_thread()
             .enable_all()
             .build()
             .unwrap();
-        temp_env::with_var("MERGIFY_TOKEN", value, || runtime.block_on(body))
+        mergify_core::env::testing::with_var("MERGIFY_TOKEN", value, || runtime.block_on(body))
     }
 }

crates/mergify-auth/src/lib.rs

@@ -111,7 +111,7 @@ mod tests {
     // the variable instead.
     #[test]
     fn the_variables_are_the_fallback() {
-        let from_windows = temp_env::with_vars(
+        let from_windows = mergify_core::env::testing::with_vars(
             [
                 ("COMPUTERNAME", Some("WIN-BOX")),
                 ("HOSTNAME", Some("ignored")),
@@ -120,13 +120,13 @@ mod tests {
         );
         assert_eq!(from_windows.as_deref(), Some("WIN-BOX"));
 
-        let from_shell = temp_env::with_vars(
+        let from_shell = mergify_core::env::testing::with_vars(
             [("COMPUTERNAME", None), ("HOSTNAME", Some("build-42"))],
             from_env,
         );
         assert_eq!(from_shell.as_deref(), Some("build-42"));
 
-        let from_nothing = temp_env::with_vars(
+        let from_nothing = mergify_core::env::testing::with_vars(
             [("COMPUTERNAME", None::<&str>), ("HOSTNAME", None)],
             from_env,
         );