node: implement heredocs + string interpolation

node.go

@@ -1465,6 +1465,19 @@ func (this *conversionState) convertNoFreeFloating(n_ node.Node) (string, error)
 
 		return quoteGoString(rawValue), nil // Go source code quoting format
 
+	case *scalar.EncapsedStringPart:
+		// The n.Value that we receive here does not contain quotes at all
+		// TODO what happens with embedded escape characters? Did the parser
+		// remove them for us already or do we just have to assume we are in
+		// a double-quoted-equivalent situation?
+		return quoteGoString(n.Value), nil // Go source code quoting format
+
+	case *scalar.Encapsed:
+		return this.convertEncapsedString(n.Parts)
+
+	case *scalar.Heredoc:
+		return this.convertEncapsedString(n.Parts)
+
 	case *scalar.MagicConstant:
 		// magic constants are case-insensitive
 		switch strings.ToLower(n.Value) {
@@ -1599,6 +1612,13 @@ func removeParens(expr string) string {
 	return expr
 }
 
+// asSingleExpression makes the expr into a single expression that is safe for
+// embedding in a larger statement e.g. multiple string concatenation.
+func asSingleExpression(expr string) string {
+	return `(` + removeParens(expr) + `)`
+	// TODO simplify this in cases where we can tell it is already a single expression e.g. quoted strings, number literals, variable literals, ...
+}
+
 func quoteGoString(s string) string {
 
 	if !strings.Contains(s, "`") && strings.Count(s, "\n") >= 3 { // TODO make the heuristic configurable
@@ -1611,6 +1631,27 @@ func quoteGoString(s string) string {
 }
 
 func (this *conversionState) convertEncapsedString(parts []node.Node) (string, error) {
+	// This is used for string interpolation: `echo "bar $ref";`
+	// And also for heredocs
+	// Child nodes are either EncapsedStringPart or expr.**
+	ret := make([]string, 0, len(parts))
+	for _, part := range parts {
+		pp, err := this.convert(part)
+		if err != nil {
+			return "", parseErr{part, err}
+		}
+
+		if _, ok := part.(*scalar.EncapsedStringPart); !ok {
+			// Subexpression - should probably parenthesise just in case
+			pp = asSingleExpression(pp)
+		}
+
+		ret = append(ret, pp)
+	}
+
+	return `(` + strings.Join(ret, ` + `) + `)`, nil
+}
+
 // resolveName turns a `*name.Name` node into a Go string.
 func (this *conversionState) resolveName(n node.Node) (string, error) {
 	// TODO support namespace lookups