fix(contrib): fix scm-prompt triggering chpwd hooks during directory traversal

[vegerot]

Summary: Currently, trying to open a new tab in Ghostty within a repository
causes the tab to open in the repository root instead of the current working
directory. This commit fixes the issue.

When scm-prompt.sh walks up the directory tree to find the root of the
repository (.sl, .git, or .hg), it uses builtin cd -P. In Zsh,
executing cd (even inside a subshell) triggers all functions registered
in chpwd_functions.

This causes unexpected side effects if a chpwd hook performs operations
that bypass standard output capture. For example, Ghostty's shell integration
registers a chpwd hook that writes an OSC 7 escape sequence directly to a
persistent TTY file descriptor (/dev/tty) to report the current working
directory. Because this writes to the TTY directly, the traversal performed by
scm-prompt.sh leaks temporary working directories to the terminal emulator,
causing Ghostty to open new tabs in the repository root rather than the actual
current working directory.

By localizing and clearing chpwd_functions within the subshell before executing
cd, we prevent these hooks from firing during the directory traversal, resolving
the side effects while keeping the traversal logic intact.

Test plan:

Run this script. Before this commit, it will print the path to the repository
root. After this commit, it will print the current working directory.

#!/usr/bin/env zsh

# Clear previous output
rm -f /tmp/ghostty_bug_repro.txt
rm -f /tmp/ghostty_log.txt

# Create a self-contained temporary home/zdotdir for this test
REPRO_ZDOTDIR=$(mktemp -d)

# Write out the minimal reproducible .zshrc
cat << 'ZSHRC_EOF' > "$REPRO_ZDOTDIR/.zshrc"
# We need prompt_subst to allow function execution in prompt
setopt prompt_subst

# Load the buggy sapling prompt (assuming it's installed at this path)
source ~/workspace/github.com/facebook/sapling/eden/scm/contrib/scm-prompt.sh

# Set the prompt to trigger the bug
export PS1='$(_scm_prompt) %~ %# '

# To test Ghostty OSC 7 tracking, we need Ghostty shell integration
source "$GHOSTTY_RESOURCES_DIR/shell-integration/zsh/ghostty-integration"
ZSHRC_EOF

# Launch Ghostty with logging and our minimal zshrc
# We use ZDOTDIR to point zsh to our custom zshrc
GHOSTTY_LOG=stderr ZDOTDIR="$REPRO_ZDOTDIR" /Users/bytedance/workspace/github.com/ghostty-org/ghostty/zig-out/Ghostty.app/Contents/MacOS/ghostty > /tmp/ghostty_log.txt 2>&1 &
GHOSTTY_PID=$!

# Give it a moment to start
sleep 1

# Run the AppleScript to drive the UI
osascript << 'APPLESCRIPT'
tell application "System Events"
    tell application "/Users/bytedance/workspace/github.com/ghostty-org/ghostty/zig-out/Ghostty.app" to activate
    delay 1

    -- cd to a deeply nested directory in the sapling repo
    keystroke "cd ~/workspace/github.com/facebook/sapling/eden/scm/"
    keystroke return
    delay 1

    -- open a new tab
    keystroke "t" using command down
    delay 1

    -- get the pwd in the new tab and write it to a file
    keystroke "pwd > /tmp/ghostty_bug_repro.txt"
    keystroke return
    delay 1

    -- quit Ghostty
    keystroke "q" using command down
end tell
APPLESCRIPT

# Read the output
echo "The new tab's working directory was:"
cat /tmp/ghostty_bug_repro.txt

echo "Ghostty PID was $GHOSTTY_PID"

echo "Ghostty logs are in: /tmp/ghostty_log.txt"

# Clean up
rm -rf "$REPRO_ZDOTDIR"

Co-authored-by: Trae trae@bytedance.com

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates SCM prompt path-canonicalization to avoid chpwd_functions side effects while walking up parent directories.

Changes:

• Clears chpwd_functions before builtin cd -P during the prompt’s “realpath” loop to suppress Zsh chpwd hook execution in that subshell.

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[facebook-github-tools]

@vegerot has updated the pull request. You must reimport the pull request before landing.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

[meta-codesync]

@facebook-github-bot has imported this pull request. If you are a Meta employee, you can view this in D106557429. (Because this pull request was imported automatically, there will not be any future comments.)

[facebook-github-tools]

@vegerot has updated the pull request. You must reimport the pull request before landing.

[quark-zju]

Review automatically exported from Phabricator review in Meta.

[meta-codesync]

This pull request has been merged in e4453e0.