fix(shell): don't exec tmux during VS Code's shell-env probe #73

2026-07-14T16:44:20+01:00

lyrathorpe commented

2026-07-14 16:44:20 +01:00

Problem

On the macOS host, VS Code fails to open a terminal on startup with:

Unable to resolve your shell environment: Unexpected exit code from spawned shell (code 1, signal null)

macOS GUI apps don't inherit a shell environment, so VS Code resolves it at
startup by spawning an interactive login shell to harvest env vars. That
probe runs with stdout piped and no controlling terminal.

The order-200 auto-tmux block in home/shell.nix treated the probe as a normal
interactive shell and ran exec tmux new-session -A -s main. Without a tty,
tmux exits with open terminal failed: not a terminal (non-zero), so VS Code
reports the error above. Linux/WSL is unaffected because VS Code Remote inherits
its environment and skips the probe.

Fix

Add two guards to the tmux exec:

[[ -t 1 ]] — only exec when stdout is a real terminal (the probe's stdout is
a pipe, so it is skipped).
[[ -z "$VSCODE_RESOLVING_ENVIRONMENT" ]] — skip VS Code's env-resolution
probe explicitly, covering the case where a future version hands it a pty.

Real terminals still land in tmux; the integrated terminal was already exempt
via the existing TERM_PROGRAM != vscode check.

Verification

Reproduced the probe locally: piped, no-tty interactive login zsh printed
open terminal failed: not a terminal and swallowed the env output.
Confirmed [[ -t 1 ]] is false in that probe and true in a real terminal.
nix fmt clean; darwinConfigurations.lyrathorpe-mac evaluates.

## Problem On the macOS host, VS Code fails to open a terminal on startup with: > Unable to resolve your shell environment: Unexpected exit code from spawned shell (code 1, signal null) macOS GUI apps don't inherit a shell environment, so VS Code resolves it at startup by spawning an **interactive login shell** to harvest env vars. That probe runs with stdout piped and **no controlling terminal**. The order-200 auto-tmux block in `home/shell.nix` treated the probe as a normal interactive shell and ran `exec tmux new-session -A -s main`. Without a tty, tmux exits with `open terminal failed: not a terminal` (non-zero), so VS Code reports the error above. Linux/WSL is unaffected because VS Code Remote inherits its environment and skips the probe. ## Fix Add two guards to the tmux exec: - `[[ -t 1 ]]` — only exec when stdout is a real terminal (the probe's stdout is a pipe, so it is skipped). - `[[ -z "$VSCODE_RESOLVING_ENVIRONMENT" ]]` — skip VS Code's env-resolution probe explicitly, covering the case where a future version hands it a pty. Real terminals still land in tmux; the integrated terminal was already exempt via the existing `TERM_PROGRAM != vscode` check. ## Verification - Reproduced the probe locally: piped, no-tty interactive login zsh printed `open terminal failed: not a terminal` and swallowed the env output. - Confirmed `[[ -t 1 ]]` is false in that probe and true in a real terminal. - `nix fmt` clean; `darwinConfigurations.lyrathorpe-mac` evaluates.

lyrathorpe added 1 commit 2026-07-14 16:44:20 +01:00

fix(shell): don't exec tmux during VS Code's shell-env probe

CI / flake (pull_request) Successful in 3m46s

Details

2125dd7aac

VS Code on macOS resolves the shell environment at startup by running an
interactive login shell with stdout piped and no controlling terminal.
The order-200 auto-tmux block treated that probe as a normal interactive
shell and ran `exec tmux new-session`, which fails without a tty ("open
terminal failed: not a terminal") and exits non-zero. VS Code then reports
"Unable to resolve your shell environment: Unexpected exit code from
spawned shell (code 1)".

Gate the exec on a real terminal (-t 1) and skip it when
VSCODE_RESOLVING_ENVIRONMENT is set. Real terminals still land in tmux;
the integrated terminal was already exempt via TERM_PROGRAM.

lyrathorpe scheduled this pull request to auto merge when all checks succeed 2026-07-14 16:44:36 +01:00

lyrathorpe merged commit 432a00fb35 into main

2026-07-14 16:48:16 +01:00

lyrathorpe deleted branch fix/vscode-shell-env-tmux-guard

2026-07-14 16:48:17 +01:00

Sign in to join this conversation.

1 Participants

Notifications

Due Date

No due date set.

Dependencies

No dependencies set.

Reference: lyrathorpe/nixfiles#73