hcl/scanner: scan interpolations properly

hcl/scanner/scanner.go

@@ -375,6 +375,7 @@ func (s *Scanner) scanExponent(ch rune) rune {
 
 // scanString scans a quoted string
 func (s *Scanner) scanString() {
+	braces := 0
 	for {
 		// '"' opening already consumed
 		// read character after quote
@@ -385,10 +386,21 @@ func (s *Scanner) scanString() {
 			return
 		}
 
-		if ch == '"' {
+		if ch == '"' && braces == 0 {
 			break
 		}
 
+		// If we're going into a ${} then we can ignore quotes for awhile
+		if braces == 0 && ch == '$' && s.peek() == '{' {
+			braces++
+			s.next()
+		} else if braces > 0 && ch == '{' {
+			braces++
+		}
+		if braces > 0 && ch == '}' {
+			braces--
+		}
+
 		if ch == '\\' {
 			s.scanEscape()
 		}

hcl/scanner/scanner_test.go

@@ -74,6 +74,7 @@ var tokenLists = map[string][]tokenPair{
 		{token.STRING, `" "`},
 		{token.STRING, `"a"`},
 		{token.STRING, `"本"`},
+		{token.STRING, `"${file("foo")}"`},
 		{token.STRING, `"\a"`},
 		{token.STRING, `"\b"`},
 		{token.STRING, `"\f"`},