interp: drop muesli/cancelreader for os.File.SetReadDeadline

The docs for SetReadDeadline are very clear:

    SetReadDeadline sets the deadline for future Read calls
    and any currently-blocked Read call.

Given that it works for any currently blocked Read call as well,
we don't need all the extra machinery and code from cancelreader.
Particularly now that Reader.stdin is always a file.

go.mod

@@ -7,7 +7,6 @@ require (
 	github.com/go-quicktest/qt v1.101.0
 	github.com/google/go-cmp v0.6.0
 	github.com/google/renameio/v2 v2.0.0
-	github.com/muesli/cancelreader v0.2.2
 	github.com/rogpeppe/go-internal v1.13.1
 	golang.org/x/sync v0.9.0
 	golang.org/x/sys v0.27.0

go.sum

@@ -11,8 +11,6 @@ github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
-github.com/muesli/cancelreader v0.2.2 h1:3I4Kt4BQjOR54NavqnDogx/MIoWBFa0StPA8ELUXHmA=
-github.com/muesli/cancelreader v0.2.2/go.mod h1:3XuTXfFS2VjM+HTLZY9Ak0l6eUKfijIfMUZ4EgX0QYo=
 github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/rogpeppe/go-internal v1.13.1 h1:KvO1DLK/DRN07sQ1LQKScxyZJuNnedQ5/wKSR38lUII=

interp/builtin.go

@@ -10,14 +10,13 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"io"
 	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
 	"syscall"
+	"time"
 
-	"github.com/muesli/cancelreader"
 	"golang.org/x/term"
 
 	"mvdan.cc/sh/v3/expand"
@@ -942,39 +941,22 @@ func (r *Runner) readLine(ctx context.Context, raw bool) ([]byte, error) {
 	var line []byte
 	esc := false
 
-	stdin := io.Reader(r.stdin)
-	// [cancelreader.NewReader] may fail under some circumstances, such as r.stdin being
-	// a regular file on Linux, in which case epoll returns an "operation not permitted" error
-	// given that regular files can always be read immediately. Polling them makes no sense.
-	// As such, if cancelreader fails, fall back to no cancellation, meaning this is best-effort.
-	//
-	// TODO: it would be nice if the cancelreader library classified errors so that we could
-	// safely handle "this file does not need polling" by skipping the polling as we do below
-	// but still fail on other errors, which may be unexpected or hide bugs.
-	// See the upstream issue: https://github.com/muesli/cancelreader/issues/23
-	if cr, err := cancelreader.NewReader(r.stdin); err == nil {
-		stopc := make(chan struct{})
-		stop := context.AfterFunc(ctx, func() {
-			cr.Cancel()
-			close(stopc)
-		})
-		defer func() {
-			if !stop() {
-				// The AfterFunc was started; wait for it to complete and close the cancel reader.
-				// Could put the Close in the above goroutine, but if "read" is
-				// immediately called again, the Close might overlap with creating a
-				// new cancelreader. Want this cancelreader to be completely closed
-				// by the time readLine returns.
-				<-stopc
-				cr.Close()
-			}
-		}()
-		stdin = cr
-	}
-
+	stopc := make(chan struct{})
+	stop := context.AfterFunc(ctx, func() {
+		r.stdin.SetReadDeadline(time.Now())
+		close(stopc)
+	})
+	defer func() {
+		if !stop() {
+			// The AfterFunc was started.
+			// Wait for it to complete, and reset the file's deadline.
+			<-stopc
+			r.stdin.SetReadDeadline(time.Time{})
+		}
+	}()
 	for {
 		var buf [1]byte
-		n, err := stdin.Read(buf[:])
+		n, err := r.stdin.Read(buf[:])
 		if n > 0 {
 			b := buf[0]
 			switch {