pkg/eval: Check FD when using it as redir source.

This fixes #788.

pkg/eval/compile_effect.go

@@ -478,6 +478,10 @@ type redirOp struct {
 	flag    int
 }
 
+type invalidFD struct{ fd int }
+
+func (err invalidFD) Error() string { return fmt.Sprintf("invalid fd: %d", err.fd) }
+
 func (op *redirOp) invoke(fm *Frame) error {
 	var dst int
 	if op.dstOp.body == nil {
@@ -509,10 +513,13 @@ func (op *redirOp) invoke(fm *Frame) error {
 		if err != nil {
 			return err
 		}
-		if src == -1 {
+		switch {
+		case src == -1:
 			// close
 			fm.ports[dst] = &Port{}
-		} else {
+		case src >= len(fm.ports) || fm.ports[src] == nil:
+			return invalidFD{src}
+		default:
 			fm.ports[dst] = fm.ports[src].Fork()
 		}
 	} else {

pkg/eval/compile_effect_test.go

@@ -1,8 +1,15 @@
 package eval
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/elves/elvish/pkg/util"
+)
 
 func TestCompileEffect(t *testing.T) {
+	_, cleanup := util.InTestDir()
+	defer cleanup()
+
 	Test(t,
 		// Chunks
 		// ------
@@ -67,21 +74,26 @@ func TestCompileEffect(t *testing.T) {
 		// Redirections
 		// ------------
 
-		That("f=(mktemp elvXXXXXX); echo 233 > $f; cat < $f; rm $f").
-			Prints("233\n"),
-
+		That("echo 233 > out1", " slurp < out1").
+			Puts("233\n"),
 		// Redirections from special form.
-		That(`f = (mktemp elvXXXXXX)`,
-			`for x [lorem ipsum] { echo $x } > $f`,
-			`cat $f`,
-			`rm $f`).Prints("lorem\nipsum\n"),
-
+		That(`for x [lorem ipsum] { echo $x } > out2`, `slurp < out2`).
+			Puts("lorem\nipsum\n"),
+		// Using numeric FDs as source and destination.
+		That(`{ echo foobar >&2 } 2> out3`, `slurp < out3`).
+			Puts("foobar\n"),
+		// Using named FDs as source and destination.
+		That(`{ echo foobar >&stderr } stderr> out4`, `slurp < out4`).
+			Puts("foobar\n"),
+		// Using a new FD as source throws an exception.
+		That(`echo foo >&4`).ThrowsAny(),
+		// Using a new FD as destination is OK, and makes it available.
+		That(`{ echo foo >&4 } 4>out5`, `slurp < out5`).Puts("foo\n"),
 		// Redirections from File object.
-		That(`fname=(mktemp elvXXXXXX); echo haha > $fname;
-			f=(fopen $fname); cat <$f; fclose $f; rm $fname`).Prints("haha\n"),
-
+		That(`echo haha > out3`, `f = (fopen out3)`, `slurp <$f`, ` fclose $f`).
+			Puts("haha\n"),
 		// Redirections from Pipe object.
-		That(`p=(pipe); echo haha > $p; pwclose $p; cat < $p; prclose $p`).
-			Prints("haha\n"),
+		That(`p = (pipe); echo haha > $p; pwclose $p; slurp < $p; prclose $p`).
+			Puts("haha\n"),
 	)
 }

pkg/eval/frame.go

@@ -121,7 +121,9 @@ func linesToChan(r io.Reader, ch chan<- interface{}) {
 func (fm *Frame) fork(name string) *Frame {
 	newPorts := make([]*Port, len(fm.ports))
 	for i, p := range fm.ports {
-		newPorts[i] = p.Fork()
+		if p != nil {
+			newPorts[i] = p.Fork()
+		}
 	}
 	return &Frame{
 		fm.Evaler, fm.srcMeta,