Implement backtick expansion

commands/shell/quotes.go

@@ -12,6 +12,9 @@ func (p *QuoteParameters) SubParsers() []Parser {
 		&BaseParser{
 			parameters: &DollarParameters{},
 		},
+		&BaseParser{
+			parameters: &BacktickParameters{},
+		},
 		&BaseParser{
 			parameters: &CharParserParameters{},
 		},

commands/shell/quotes_test.go

@@ -27,7 +27,8 @@ func (t *QuotesTest) TestParse() {
 	t.NoError(err)
 
 	expanded, _ := token.(Expandable).Expand(nil, nil, nil)
-	t.Equal("word1 word2    word3\n word4", strings.Join(expanded, " "))
+	t.Equal(1, len(expanded))
+	t.Equal("word1 word2    word3\n word4", expanded[0])
 }
 
 func (t *QuotesTest) TestExpandVariables() {
@@ -72,6 +73,52 @@ func (t *QuotesTest) TestExpandSubshell() {
 	t.Equal("This is a subshell", expanded[0])
 }
 
+func (t *QuotesTest) TestExpandBacktick() {
+	parser := &BaseParser{&QuoteParameters{}}
+	reader := bufio.NewReader(
+		strings.NewReader("\"This is `echo a backtick`\""),
+	)
+
+	state := NewShellState()
+
+	echo := &builtins.Echo{}
+	state.SetCommand(echo.Name(), echo)
+
+	iterator, err := NewCharIterator(reader)
+	t.NoError(err)
+
+	token, err := parser.Parse(iterator, &CharCollection{})
+	t.NoError(err)
+
+	expanded, _ := token.(Expandable).Expand(state, nil, nil)
+	t.Equal(1, len(expanded))
+	t.Equal("This is a backtick", expanded[0])
+}
+
+// The only way backticks can be nested at the moment is by wrapping them in
+// quotes.
+func (t *QuotesTest) TestExpandNestedBacktick() {
+	parser := &BaseParser{&QuoteParameters{}}
+	reader := bufio.NewReader(
+		strings.NewReader("\"This is `echo a \"`echo backtick`\"`\""),
+	)
+
+	state := NewShellState()
+
+	echo := &builtins.Echo{}
+	state.SetCommand(echo.Name(), echo)
+
+	iterator, err := NewCharIterator(reader)
+	t.NoError(err)
+
+	token, err := parser.Parse(iterator, &CharCollection{})
+	t.NoError(err)
+
+	expanded, _ := token.(Expandable).Expand(state, nil, nil)
+	t.Equal(1, len(expanded))
+	t.Equal("This is a backtick", expanded[0])
+}
+
 func TestQuotesTest(t *testing.T) {
 	suite.Run(t, new(QuotesTest))
 }

commands/shell/subshell.go

@@ -1,6 +1,7 @@
 package shell
 
 import (
+	"bytes"
 	"io"
 	"log"
 )
@@ -64,11 +65,17 @@ func (s *Subshell) Evaluate(state State, stdin io.Reader, stdout io.Writer, stde
 }
 
 type Backtick struct {
-	Subshell
+	BaseToken
 }
 
-type BacktickParameters struct {
-	SubshellParameters
+type BacktickParameters struct{}
+
+func (p *BacktickParameters) MakeToken() Token {
+	return &Backtick{}
+}
+
+func (p *BacktickParameters) Enter(i *CharIterator) error {
+	return i.Next()
 }
 
 func (p *BacktickParameters) Supports(charsBefore []rune, r rune) bool {
@@ -88,3 +95,53 @@ func (p *BacktickParameters) ShouldLeave(charsBefore []rune, r rune) bool {
 
 	return false
 }
+
+func (b *Backtick) Expand(state State, stdin io.Reader, stderr io.Writer) ([]string, uint8) {
+	var ret uint8
+	stdout := bytes.NewBuffer([]byte{})
+
+	for _, token := range b.Tokens() {
+		if eval, ok := token.(Evalable); ok {
+			ret = state.Eval(eval, stdin, stdout, stderr)
+		} else {
+			logstr := "shell: Unexpected token: " + token.String()
+			log.Println(logstr)
+			stderr.Write([]byte(logstr))
+		}
+	}
+
+	return []string{stdout.String()}, ret
+}
+
+func (p *BacktickParameters) SubParsers() []Parser {
+	return []Parser{
+		&BaseParser{
+			parameters: &StatementInsideBacktickparameters{},
+		},
+	}
+}
+
+type StatementInsideBacktickparameters struct {
+	StatementParameters
+}
+
+// Note: this is a bit of a hack. There is no way to know whether the new
+// backtick is supposed to open a new backtick statement within the backtick, or
+// close the current one. At least not in the current implementation that
+// doesn't allow us to look ahead. Which means that backticks inside backticks
+// are not supported.
+func (p *StatementInsideBacktickparameters) ShouldLeave(charsBefore []rune, r rune) bool {
+	if r == '\n' || r == ';' || r == ')' || r == '`' {
+		return countBackslashSuffixes(charsBefore)%2 == 0
+	}
+
+	return false
+}
+
+func (p *StatementInsideBacktickparameters) Leave(i *CharIterator) error {
+	if i.Current() == '`' {
+		return i.Previous()
+	}
+
+	return nil
+}