Fix tmux panic (#165)

Fix `tmux` sessions

This will create a new session named `topgrade`, `topgrade-1`,
`topgrade-2`, using the first nonexistent session name it finds. That
session will have a window in it named `topgrade` in which `topgrade` is
run. If `topgrade --tmux` is being run from within tmux, it won't attach
to the new tmux session. If the user is not currently in tmux, it will
attach to the newly-created session.

Co-authored-by: Thomas Schönauer <37108907+DottoDev@users.noreply.github.com>

src/execution_context.rs

@@ -6,6 +6,7 @@ use crate::{config::Config, executor::Executor};
 use color_eyre::eyre::Result;
 use directories::BaseDirs;
 use std::path::{Path, PathBuf};
+use std::sync::Mutex;
 
 pub struct ExecutionContext<'a> {
     run_type: RunType,
@@ -13,6 +14,10 @@ pub struct ExecutionContext<'a> {
     git: &'a Git,
     config: &'a Config,
     base_dirs: &'a BaseDirs,
+    /// Name of a tmux session to execute commands in, if any.
+    /// This is used in `./steps/remote/ssh.rs`, where we want to run `topgrade` in a new
+    /// tmux window for each remote.
+    tmux_session: Mutex<Option<String>>,
 }
 
 impl<'a> ExecutionContext<'a> {
@@ -22,13 +27,14 @@ impl<'a> ExecutionContext<'a> {
         git: &'a Git,
         config: &'a Config,
         base_dirs: &'a BaseDirs,
-    ) -> ExecutionContext<'a> {
-        ExecutionContext {
+    ) -> Self {
+        Self {
             run_type,
             sudo,
             git,
             config,
             base_dirs,
+            tmux_session: Mutex::new(None),
         }
     }
 
@@ -67,4 +73,12 @@ impl<'a> ExecutionContext<'a> {
     pub fn base_dirs(&self) -> &BaseDirs {
         self.base_dirs
     }
+
+    pub fn set_tmux_session(&self, session_name: String) {
+        self.tmux_session.lock().unwrap().replace(session_name);
+    }
+
+    pub fn get_tmux_session(&self) -> Option<String> {
+        self.tmux_session.lock().unwrap().clone()
+    }
 }