feat: set the program environment variables (#1063)

This gives the option to provide a custom set of environment variables
to use in the Bubble Tea program. When running Bubble Tea in a remote
session such as SSH, we need to be able to pass the SSH session's
environment variables rather than the server ones.

options.go

@@ -49,6 +49,23 @@ func WithInputTTY() ProgramOption {
  }
 }
 
+// WithEnvironment sets the environment variables that the program will use.
+// This useful when the program is running in a remote session (e.g. SSH) and
+// you want to pass the environment variables from the remote session to the
+// program.
+//
+// Example:
+//
+// var sess ssh.Session // ssh.Session is a type from the github.com/charmbracelet/ssh package
+// pty, _, _ := sess.Pty()
+// environ := append(sess.Environ(), "TERM="+pty.Term)
+// p := tea.NewProgram(model, tea.WithEnvironment(environ)
+func WithEnvironment(env []string) ProgramOption {
+ return func(p *Program) {
+ p.environ = env
+ }
+}
+
 // WithoutSignalHandler disables the signal handler that Bubble Tea sets up for
 // Programs. This is useful if you want to handle signals yourself.
 func WithoutSignalHandler() ProgramOption {

tea.go

@@ -151,6 +151,9 @@ type Program struct {
  previousOutputState *term.State
  renderer renderer
 
+ // the environment variables for the program, defaults to os.Environ().
+ environ []string
+
  // where to read inputs from, this will usually be os.Stdin.
  input io.Reader
  // ttyInput is null if input is not a TTY.
@@ -222,6 +225,11 @@ func NewProgram(model Model, opts ...ProgramOption) *Program {
  p.output = os.Stdout
  }
 
+ // if no environment was set, set it to os.Environ()
+ if p.environ == nil {
+ p.environ = os.Environ()
+ }
+
  return p
 }