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prompt.go
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prompt.go
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// Package prompt implements the prompt subsystem of the editor.
package prompt
import (
"io/ioutil"
"math"
"os"
"sync"
"time"
"github.com/u-root/u-root/cmds/core/elvish/edit/eddefs"
"github.com/u-root/u-root/cmds/core/elvish/edit/ui"
"github.com/u-root/u-root/cmds/core/elvish/eval"
"github.com/u-root/u-root/cmds/core/elvish/eval/vals"
"github.com/u-root/u-root/cmds/core/elvish/eval/vars"
"github.com/u-root/u-root/cmds/core/elvish/util"
)
var logger = util.GetLogger("[edit/prompt] ")
// Init initializes the prompt subsystem of the editor.
func Init(ed eddefs.Editor, ns eval.Ns) {
prompt := makePrompt(ed, defaultPrompt)
rprompt := makePrompt(ed, defaultRPrompt)
ed.SetPrompt(prompt)
ed.SetRPrompt(rprompt)
installAPI(ns, prompt, "prompt")
installAPI(ns, rprompt, "rprompt")
}
func installAPI(ns eval.Ns, p *prompt, basename string) {
ns.Add(basename, vars.FromPtr(&p.fn))
ns.Add(basename+"-stale-threshold", vars.FromPtr(&p.staleThreshold))
ns.Add(basename+"-stale-transform", vars.FromPtr(&p.staleTransform))
ns.Add("-"+basename+"-eagerness", vars.FromPtr(&p.eagerness))
}
type prompt struct {
ed eddefs.Editor
// The main callback.
fn eval.Callable
// Callback used to transform stale prompts.
staleTransform eval.Callable
// Threshold in seconds for a prompt to be considered as stale.
staleThreshold float64
// How eager the prompt should be updated. When >= 5, updated when directory
// is changed. When >= 10, always update. Default is 5.
eagerness int
// Working directory when prompt was last updated.
lastWd string
// Channel for update requests.
updateReq chan struct{}
// Channel on which prompt contents are sent.
ch chan []*ui.Styled
// Last prompt content
last []*ui.Styled
lastMutex *sync.RWMutex
}
var unknownContent = []*ui.Styled{{"???> ", ui.Styles{}}}
func makePrompt(ed eddefs.Editor, fn eval.Callable) *prompt {
p := &prompt{
ed, fn, defaultStaleTransform, 0.2, 5,
"", make(chan struct{}, 1), make(chan []*ui.Styled, 1),
unknownContent, new(sync.RWMutex)}
go p.loop()
return p
}
func (p *prompt) loop() {
content := unknownContent
ch := make(chan []*ui.Styled)
for range p.updateReq {
go func() {
ch <- callPrompt(p.ed, p.fn)
}()
select {
case <-makeMaxWaitChan(p.staleThreshold):
// The prompt callback did not finish within the threshold. Send the
// previous content, marked as stale.
p.send(callTransformer(p.ed, p.staleTransform, content))
content = <-ch
select {
case <-p.updateReq:
// If another update is already requested by the time we finish,
// keep marking the prompt as stale. This reduces flickering.
p.send(callTransformer(p.ed, p.staleTransform, content))
p.queueUpdate()
default:
p.send(content)
}
case content = <-ch:
p.send(content)
}
}
}
func (p *prompt) Chan() <-chan []*ui.Styled {
return p.ch
}
func (p *prompt) Update(force bool) {
if force || p.shouldUpdate() {
p.queueUpdate()
}
}
func (p *prompt) Last() []*ui.Styled {
p.lastMutex.RLock()
defer p.lastMutex.RUnlock()
return p.last
}
func (p *prompt) Close() error {
// TODO: Close p.updateReq. However, doing this can cause
// write-to-closed-channel panics.
return nil
}
func (p *prompt) queueUpdate() {
select {
case p.updateReq <- struct{}{}:
default:
}
}
func (p *prompt) send(content []*ui.Styled) {
p.lastMutex.Lock()
p.last = content
p.lastMutex.Unlock()
p.ch <- content
}
func (p *prompt) shouldUpdate() bool {
if p.eagerness >= 10 {
return true
}
if p.eagerness >= 5 {
wd, err := os.Getwd()
if err != nil {
wd = "error"
}
oldWd := p.lastWd
p.lastWd = wd
return wd != oldWd
}
return false
}
// maxSeconds is the maximum number of seconds time.Duration can represent.
const maxSeconds = float64(math.MaxInt64 / time.Second)
// makeMaxWaitChan makes a channel that sends the current time after f seconds.
// If f does not fits in a time.Duration value, it returns nil, which is a
// channel that never sends any value.
func makeMaxWaitChan(f float64) <-chan time.Time {
if f > maxSeconds {
return nil
}
return time.After(time.Duration(f * float64(time.Second)))
}
// callPrompt calls a function with no arguments and closed input, and converts
// its outputs to styled objects. Used to call prompt callbacks.
func callPrompt(ed eddefs.Editor, fn eval.Callable) []*ui.Styled {
ports := []*eval.Port{
eval.DevNullClosedChan,
{}, // Will be replaced when capturing output
{File: os.Stderr},
}
return callAndGetStyled(ed, fn, ports)
}
// callTransformer calls a function with no arguments and the given inputs, and
// converts its outputs to styled objects. Used to call stale transformers.
func callTransformer(ed eddefs.Editor, fn eval.Callable, currentPrompt []*ui.Styled) []*ui.Styled {
input := make(chan interface{})
stopInputWriter := make(chan struct{})
ports := []*eval.Port{
{Chan: input, File: eval.DevNull},
{}, // Will be replaced when capturing output
{File: os.Stderr},
}
go func() {
defer close(input)
for _, char := range currentPrompt {
select {
case input <- char:
case <-stopInputWriter:
return
}
}
}()
defer close(stopInputWriter)
return callAndGetStyled(ed, fn, ports)
}
func callAndGetStyled(ed eddefs.Editor, fn eval.Callable, ports []*eval.Port) []*ui.Styled {
var (
styleds []*ui.Styled
styledsMutex sync.Mutex
)
add := func(s *ui.Styled) {
styledsMutex.Lock()
styleds = append(styleds, s)
styledsMutex.Unlock()
}
// Value output may be of type ui.Styled or any other type, in which case
// they are converted to ui.Styled.
valuesCb := func(ch <-chan interface{}) {
for v := range ch {
if s, ok := v.(*ui.Styled); ok {
add(s)
} else {
add(&ui.Styled{vals.ToString(v), ui.Styles{}})
}
}
}
// Byte output is added to the prompt as a single unstyled text.
bytesCb := func(r *os.File) {
allBytes, err := ioutil.ReadAll(r)
if err != nil {
logger.Println("error reading prompt byte output:", err)
}
if len(allBytes) > 0 {
add(&ui.Styled{string(allBytes), ui.Styles{}})
}
}
// XXX There is no source to pass to NewTopEvalCtx.
ec := eval.NewTopFrame(ed.Evaler(), eval.NewInternalSource("[prompt]"), ports)
err := ec.CallWithOutputCallback(fn, nil, eval.NoOpts, valuesCb, bytesCb)
if err != nil {
ed.Notify("prompt function error: %v", err)
return nil
}
return styleds
}