fix(windows): honor default_shell in login shell mode (#4060)

* fix(windows): honor default_shell in login shell mode

Login-mode panes used portable-pty's default-program builder, which resolves to %ComSpec% (cmd.exe) on Windows and ignores the SHELL env override, so [terminal].default_shell was silently ignored. Build the launch command from the configured shell instead and append the shell's own login flag for POSIX-style shells that support one.

refs #1445

* fix(windows): add csh and tcsh to login shell flags

refs #1445

1 files changed, 123 insertions, 0 deletions

diff --git a/src/pane.rs b/src/pane.rs
index c56cfbb3..a931d3ad 100644
--- a/src/pane.rs
+++ b/src/pane.rs
@@ -1717,12 +1717,41 @@ fn resolve_shell_for_login_mode(shell: &str) -> io::Result<String> {
 /// prompt would show success after a failed command (verified on 5.1).
 pub(crate) const WINDOWS_POWERSHELL_SHELL_INTEGRATION_COMMAND: &str = r"if ($null -eq $global:__HerdrOriginalPrompt) { $global:__HerdrOriginalPrompt = $function:prompt; function global:prompt { $out = @(& $global:__HerdrOriginalPrompt) -join ' '; $loc = $ExecutionContext.SessionState.Path.CurrentLocation; if ($loc.Provider.Name -eq 'FileSystem') { try { [Environment]::CurrentDirectory = $loc.ProviderPath } catch {}; $esc = [string][char]27; $out += $esc + ']9;9;' + $loc.ProviderPath + $esc + '\' }; $out } }";
 
+/// Login flags appended when launching POSIX-style shells on Windows.
+///
+/// `portable-pty`'s default-program path resolves to `%ComSpec%` (cmd.exe) on
+/// Windows and ignores the `SHELL` env override, and the Unix argv0-prefix
+/// login convention does not exist there. A login shell therefore has to be
+/// launched directly with the shell's own login flag. Only POSIX-style shells
+/// that define one (the sh family, fish, and csh/tcsh) get it; Windows-native
+/// shells such as cmd.exe and PowerShell have no login concept and launch
+/// plain.
+fn windows_login_shell_args(shell: &str) -> &'static [&'static str] {
+    let name = shell
+        .rsplit(['/', '\\'])
+        .next()
+        .unwrap_or(shell)
+        .to_ascii_lowercase();
+    let name = name.strip_suffix(".exe").unwrap_or(&name);
+    match name {
+        "sh" | "bash" | "zsh" | "ksh" | "dash" | "ash" | "mksh" | "fish" | "csh" | "tcsh" => {
+            &["-l"]
+        }
+        _ => &[],
+    }
+}
+
 fn pane_shell_command_builder_for_target(
     shell_config: PaneShellConfig<'_>,
     target: ShellLaunchTarget,
 ) -> io::Result<CommandBuilder> {
     let shell = pane_shell(shell_config.default_shell);
     if shell_mode_uses_login_shell(shell_config.mode, target) {
+        if target == ShellLaunchTarget::Windows {
+            let mut cmd = CommandBuilder::new(&shell);
+            cmd.args(windows_login_shell_args(&shell));
+            return Ok(cmd);
+        }
         let mut cmd = CommandBuilder::new_default_prog();
         cmd.env("SHELL", resolve_shell_for_login_mode(&shell)?);
         Ok(cmd)
@@ -3809,6 +3838,100 @@ mod tests {
     }
 
     #[test]
+    fn windows_login_shell_builder_launches_configured_shell_with_login_flag() {
+        let cmd = pane_shell_command_builder_for_target(
+            PaneShellConfig::new("bash.exe", crate::config::ShellModeConfig::Login),
+            ShellLaunchTarget::Windows,
+        )
+        .unwrap();
+
+        assert!(
+            !cmd.is_default_prog(),
+            "Windows login mode must not fall back to the default program (cmd.exe)"
+        );
+        assert_eq!(
+            cmd.get_argv(),
+            &[
+                std::ffi::OsString::from("bash.exe"),
+                std::ffi::OsString::from("-l"),
+            ]
+        );
+    }
+
+    #[test]
+    fn windows_login_shell_builder_launches_native_shells_without_flag() {
+        for shell in [
+            "cmd.exe",
+            "powershell.exe",
+            "C:\\Windows\\System32\\cmd.exe",
+        ] {
+            let cmd = pane_shell_command_builder_for_target(
+                PaneShellConfig::new(shell, crate::config::ShellModeConfig::Login),
+                ShellLaunchTarget::Windows,
+            )
+            .unwrap();
+
+            assert!(!cmd.is_default_prog(), "shell {shell:?}");
+            assert_eq!(
+                cmd.get_argv(),
+                &[std::ffi::OsString::from(shell)],
+                "shell {shell:?}"
+            );
+        }
+    }
+
+    #[test]
+    fn windows_login_shell_args_maps_posix_shells_to_login_flag() {
+        for shell in [
+            "sh",
+            "sh.exe",
+            "bash",
+            "bash.exe",
+            "BASH.EXE",
+            "zsh",
+            "zsh.exe",
+            "ksh",
+            "dash",
+            "ash",
+            "mksh",
+            "fish",
+            "fish.exe",
+            "csh",
+            "csh.exe",
+            "tcsh",
+            "tcsh.exe",
+            "C:\\Program Files\\Git\\bin\\bash.exe",
+        ] {
+            assert_eq!(
+                windows_login_shell_args(shell),
+                &["-l"],
+                "shell {shell:?} should get the login flag"
+            );
+        }
+    }
+
+    #[test]
+    fn windows_login_shell_args_omits_flag_for_shells_without_login_concept() {
+        for shell in [
+            "cmd",
+            "cmd.exe",
+            "powershell",
+            "powershell.exe",
+            "pwsh",
+            "pwsh.exe",
+            "nu",
+            "nu.exe",
+            "C:\\Windows\\System32\\cmd.exe",
+        ] {
+            assert_eq!(
+                windows_login_shell_args(shell),
+                &[] as &[&str],
+                "shell {shell:?} must not get a login flag"
+            );
+        }
+    }
+
+    #[test]
     fn auto_shell_builder_keeps_direct_shell_on_non_macos_target() {
         let cmd = pane_shell_command_builder_for_target(
             PaneShellConfig::new("/bin/sh", crate::config::ShellModeConfig::Auto),