From e7be3e02aa52f2aae5dee31ea3b1ab87e9c4737c Mon Sep 17 00:00:00 2001
From: Oliver Joseph Ash <oliverjash@gmail.com>
Date: Fri, 20 Mar 2026 00:02:30 +0000
Subject: [PATCH] feat(preview): set preview subprocess size via env (#608)

* Set preview subprocess size via env
---
 internal/ui/context/command_runner.go | 10 +++++++++-
 internal/ui/preview/preview.go        |  9 ++++++++-
 test/test_command_runner.go           |  4 ++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/internal/ui/context/command_runner.go b/internal/ui/context/command_runner.go
index d5dbc77..aeff202 100644
--- a/internal/ui/context/command_runner.go
+++ b/internal/ui/context/command_runner.go
@@ -21,6 +21,7 @@ import (
 
 type CommandRunner interface {
 	RunCommandImmediate(args []string) ([]byte, error)
+	RunCommandImmediateWithEnv(args []string, env []string) ([]byte, error)
 	RunCommandStreaming(ctx context.Context, args []string) (*StreamingCommand, error)
 	RunCommand(args []string, continuations ...tea.Cmd) tea.Cmd
 	RunCommandWithInput(args []string, input string, continuations ...tea.Cmd) tea.Cmd
@@ -35,9 +36,12 @@ type MainCommandRunner struct {
 
 func (a *MainCommandRunner) nextID() int { return int(a.idCounter.Add(1)) }
 
-func (a *MainCommandRunner) RunCommandImmediate(args []string) ([]byte, error) {
+func (a *MainCommandRunner) RunCommandImmediateWithEnv(args []string, env []string) ([]byte, error) {
 	c := exec.Command("jj", args...)
 	c.Dir = a.Location
+	if len(env) > 0 {
+		c.Env = append(os.Environ(), env...)
+	}
 	if output, err := c.Output(); err != nil {
 		var exitError *exec.ExitError
 		if errors.As(err, &exitError) {
@@ -49,6 +53,10 @@ func (a *MainCommandRunner) RunCommandImmediate(args []string) ([]byte, error) {
 	}
 }
 
+func (a *MainCommandRunner) RunCommandImmediate(args []string) ([]byte, error) {
+	return a.RunCommandImmediateWithEnv(args, nil)
+}
+
 func (a *MainCommandRunner) RunCommandStreaming(ctx context.Context, args []string) (*StreamingCommand, error) {
 	c := exec.CommandContext(ctx, "jj", args...)
 	c.Dir = a.Location
diff --git a/internal/ui/preview/preview.go b/internal/ui/preview/preview.go
index fec542a..25dcb1c 100644
--- a/internal/ui/preview/preview.go
+++ b/internal/ui/preview/preview.go
@@ -219,7 +219,14 @@ func (m *Model) refreshPreviewForItem(item common.SelectedItem) tea.Cmd {
 			})
 		}
 
-		output, _ := m.context.RunCommandImmediate(args)
+		env := []string{
+			// The preview subprocess does not run in a pane-sized PTY, so let
+			// width-sensitive tools like `jj diff` see the preview size via the
+			// conventional terminal size environment variables.
+			"COLUMNS=" + strconv.Itoa(m.view.Width()),
+			"LINES=" + strconv.Itoa(m.view.Height()),
+		}
+		output, _ := m.context.RunCommandImmediateWithEnv(args, env)
 		return updatePreviewContentMsg{
 			Content: string(output),
 		}
diff --git a/test/test_command_runner.go b/test/test_command_runner.go
index ea0a855..aa53488 100644
--- a/test/test_command_runner.go
+++ b/test/test_command_runner.go
@@ -59,6 +59,10 @@ func (t *CommandRunner) RunCommandImmediate(args []string) ([]byte, error) {
 	return nil, nil
 }
 
+func (t *CommandRunner) RunCommandImmediateWithEnv(args []string, _ []string) ([]byte, error) {
+	return t.RunCommandImmediate(args)
+}
+
 func (t *CommandRunner) RunCommandStreaming(_ context.Context, args []string) (*appContext.StreamingCommand, error) {
 	reader, err := t.RunCommandImmediate(args)
 	return &appContext.StreamingCommand{