lazygit/pkg/gui/main_view_render.go

package gui

import (
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"runtime"
	"strings"

	"github.com/jesseduffield/lazygit/pkg/config"
	"github.com/jesseduffield/lazygit/pkg/gocui"
	"github.com/jesseduffield/lazygit/pkg/tasks"
	"github.com/samber/lo"
)

// renderSpec describes a render of a command's output into a view: what a way
// of running the command (see runRender) needs to know about it.
type renderSpec struct {
	view *gocui.View
	cmd  *exec.Cmd
	// The width the renderer lays its rendering out to, and the width the view
	// counts its own wrapping against. Read after the layout pass, which
	// settles it.
	width int
	// The configured stdin filter, empty unless one is configured. How git gets
	// to run it depends on the way the render runs. An external diff renderer
	// is named to git in the environment before the render is set up, whichever
	// way it runs, so it doesn't appear here; nothing else is a command of its
	// own.
	stdinFilter string
}

// newRenderTask renders cmd's output into view, through the diff renderer the
// user has configured. The renderer lays its rendering out to the width of the
// view, which only the layout settles, so the task is created after it.
func (gui *Gui) newRenderTask(view *gocui.View, cmd *exec.Cmd, prefix string) error {
	// Ask whatever renders the diff to state, in an OSC 1717 record per line,
	// which line of which file it is rendering. This lets us act on the line the
	// user is pointing at even when the rendering no longer looks like a diff.
	// The variable names the protocol versions we understand, and a renderer
	// that doesn't understand it ignores it, so we can set it always. It has to
	// be set before the plain path below, since on that path git renders the
	// diff itself, and git speaks the protocol too, for its word-diff formats,
	// whose markup we could not otherwise resolve.
	cmd.Env = append(cmd.Env, "OSC1717=V1")

	if gui.stateAccessor.GetDiffRendererConfigManager().GetDiffRendererType() == config.DiffRendererType_RawGit {
		// If we're not using a custom diff renderer, then we don't need to use a pty
		return gui.newCmdTask(view, cmd, prefix)
	}

	// The key the render is remembered under says which diff it is of, so that a
	// re-render of the same diff can be told from a render of another one. Take
	// it before anything else can touch the command's arguments.
	cmdStr := strings.Join(cmd.Args, " ")

	// Mark the view as loading synchronously now, before the layout pass: the
	// actual task is created in afterLayout (below), which runs after layout, so
	// without this the next layout pass would clamp the scroll position to the
	// not-yet-loaded content.
	gui.getManager(view).StartLoading()
	// Hold the scrollbar at its current height while the re-render loads, so the
	// thumb doesn't shrink and snap back when the first partial paint swaps in
	// (see the matching call in newCmdTask).
	view.FreezeScrollbarHeight()

	// Run the render after layout so that it gets the correct size
	gui.afterLayout(func() error {
		// The layout may have changed the size of the view, so only now is the
		// width to render at known, and with it the renderer command.
		width := view.InnerWidth()
		diffRendererConfigManager := gui.stateAccessor.GetDiffRendererConfigManager()
		values := config.DiffRendererValues{
			Width:           width,
			DiffContext:     gui.c.UserConfig().Git.DiffContextSize,
			LightBackground: gui.terminalHasLightBackground(),
		}
		stdinFilter, stdinFilterErr := diffRendererConfigManager.GetStdinFilterCommand(values)
		externalDiff, externalDiffErr := diffRendererConfigManager.GetExternalDiffCommand(values)
		if err := errors.Join(stdinFilterErr, externalDiffErr); err != nil {
			// The commands are checked with made-up values when the config is
			// loaded, so only one that fails for some values and not for others
			// gets here. Git's own diff is shown instead.
			gui.c.ErrorToast(err.Error())
		}

		// This communicates to diff renderers that we're in a very simple
		// terminal that they should not expect to have much capabilities.
		// Moving the cursor, clearing the screen, or querying for colors are among such "advanced" capabilities.
		// Context: https://github.com/jesseduffield/lazygit/issues/3419
		cmd.Env = removeExistingTermEnvVars(cmd.Env)
		cmd.Env = append(cmd.Env, "TERM=dumb")

		// An external diff command is named to git here, in the environment,
		// because the width it renders at is only known after the layout, and
		// the command's arguments were settled before it. An empty command
		// means the user wants git's own diff.external config to apply, so
		// leave the variable unset in that case; git takes it being set at all
		// as an instruction, however little it says.
		if externalDiff != "" {
			cmd.Env = append(cmd.Env, "GIT_EXTERNAL_DIFF="+externalDiff)
		}

		spec := renderSpec{
			view:        view,
			cmd:         cmd,
			width:       width,
			stdinFilter: stdinFilter,
		}
		run := gui.ptyRender
		if rendersThroughAPipe() {
			run = gui.pipedRender
		}
		return gui.newTaskForRender(spec, prefix, cmdStr, run)
	})

	return nil
}

// The start and onClose functions a render hands to its task: how to get the
// command running and the output reader for it, and how to tear it down again
// once the task is stopped.
type (
	startRender   func() (tasks.Cmd, io.Reader)
	onCloseRender func()
)

// runRender is a way of running a render's command and getting at its output:
// plainly, in a pty, or through a pipe with the stdin filter as a command of our
// own. It returns the functions the task drives the command by.
type runRender func(spec renderSpec) (startRender, onCloseRender)

// newTaskForRender creates the task that reads the render's output into its
// view, running the command the given way. key names what is rendered, so that
// a re-render of the same content can be told from a render of other content.
func (gui *Gui) newTaskForRender(spec renderSpec, prefix string, key string, run runRender) error {
	setColumnsEnvVar(spec.cmd, spec.width)

	start, onClose := run(spec)

	manager := gui.getManager(spec.view)
	linesToRead := gui.linesToReadFromCmdTask(spec.view)
	return manager.NewTask(manager.NewCmdTask(start, prefix, linesToRead, onClose), key)
}

// renderWithoutPtyEnvVar makes a render take the piped path on a platform that
// would otherwise use a pty, so that tests can exercise it anywhere.
const renderWithoutPtyEnvVar = "LAZYGIT_RENDER_WITHOUT_PTY"

// rendersThroughAPipe reports whether a render feeds the diff renderer the
// command's output through a pipe rather than running it in a pty.
//
// On Windows it has to. ConPTY doesn't pass a command's output through; it
// parses it into a screen buffer and re-encodes that for the terminal side,
// and it hands a sequence it can't represent there the moment it parses it,
// separately from the text around it. So what a renderer writes is not what
// lazygit reads. A pipe carries the bytes as the renderer wrote them.
//
// Everywhere else the pty is kept, since a renderer can read the width it
// should lay out to off it, and a configuration that doesn't name a width would
// otherwise render at whatever width the renderer falls back to.
func rendersThroughAPipe() bool {
	return runtime.GOOS == "windows" || os.Getenv(renderWithoutPtyEnvVar) != ""
}

// pipedRender feeds the diff renderer the command's output through a pipe.
//
// A stdin filter becomes a command of our own here, because git only invokes
// the one named by GIT_PAGER when it thinks it is talking to a terminal, so
// with a pipe the filter would never run. An external diff renderer is git's
// own business, named in the environment and run by git per file, so with one
// the command runs alone.
func (gui *Gui) pipedRender(spec renderSpec) (startRender, onCloseRender) {
	if spec.stdinFilter == "" {
		return gui.plainRender(spec)
	}

	view := spec.view
	cmd := spec.cmd

	var pipe io.ReadCloser
	start := func() (tasks.Cmd, io.Reader) {
		// See the matching call in ptyRender for why this happens here.
		view.SetContentWidth(spec.width)

		// The filter runs in a plain shell, without lazygit's shell functions
		// sourced, since that is the shell git would have run it in. It is
		// handed git's environment for the same reason: as git's child it
		// would have inherited exactly that.
		pipeline, reader, err := gui.os.StartPipeline(
			gui.os.Cmd.NewFromCmd(cmd).DontLog(),
			gui.os.Cmd.NewShell(spec.stdinFilter, "").SetEnviron(cmd.Env).DontLog(),
		)
		if err != nil {
			gui.c.Log.Error(err)
			// The command has been started and stopped again by now, so it
			// can't be run a second time without the renderer. Show what went
			// wrong where the diff would have been.
			return tasks.ExecCmd{Cmd: cmd}, strings.NewReader(err.Error())
		}
		pipe = reader
		return pipeline, reader
	}

	onClose := func() {
		// Closing the reader brings the pipeline down. The renderer's next write
		// fails, so it exits, and git's write into the pipe the renderer was
		// reading fails in turn.
		if pipe != nil {
			pipe.Close()
			pipe = nil
		}
	}

	return start, onClose
}

// setColumnsEnvVar tells a command how wide the view its output goes into is.
// git reads COLUMNS in preference to the size of the terminal it is talking to,
// and lays the diffstat graph out to it; a diff renderer with no terminal to
// ask may read it too (difftastic and diff-so-fancy do, delta does not). A
// command told nothing renders for 80 columns.
func setColumnsEnvVar(cmd *exec.Cmd, width int) {
	cmd.Env = append(cmd.Env, fmt.Sprintf("COLUMNS=%d", width))
}

func removeExistingTermEnvVars(env []string) []string {
	return lo.Filter(env, func(envVar string, _ int) bool {
		return !isTermEnvVar(envVar)
	})
}

// Terminals set a variety of different environment variables
// to identify themselves to processes. This list should catch the most common among them.
func isTermEnvVar(envVar string) bool {
	return strings.HasPrefix(envVar, "TERM=") ||
		strings.HasPrefix(envVar, "TERM_PROGRAM=") ||
		strings.HasPrefix(envVar, "TERM_PROGRAM_VERSION=") ||
		strings.HasPrefix(envVar, "TERMINAL_EMULATOR=") ||
		strings.HasPrefix(envVar, "TERMINAL_NAME=") ||
		strings.HasPrefix(envVar, "TERMINAL_VERSION_")
}