Remove use of sprintf in formatter

Do not format strings before writing them to output. String formatting
was only being used for concatenation and caused problems for Rego
strings that contain printf verbs.

format/format.go

@@ -378,12 +378,12 @@ func (w *writer) writeFunctionCall(t []*ast.Term, comments []*ast.Comment) []*as
 			fallthrough
 		case 2:
 			comments = w.writeTerm(t[1], comments)
-			w.write(" %s ", string(bi.Infix))
+			w.write(" " + string(bi.Infix) + " ")
 			return w.writeTerm(t[2], comments)
 		}
 	}
 
-	w.write("%s(", string(t[0].Value.(ast.String)))
+	w.write(string(t[0].Value.(ast.String)) + "(")
 	for _, v := range t[1 : len(t)-1] {
 		comments = w.writeTerm(v, comments)
 		w.write(", ")
@@ -425,7 +425,7 @@ func (w *writer) writeTerm(term *ast.Term, comments []*ast.Comment) []*ast.Comme
 	case ast.String:
 		if term.Location.Text[0] == '.' {
 			// This string was parsed from a ref, so preserve the value.
-			w.write(`"%s"`, string(x))
+			w.write(`"` + string(x) + `"`)
 		} else {
 			// To preserve raw strings, we need to output the original text,
 			// not what x.String() would give us.
@@ -901,18 +901,17 @@ func (w *writer) blankLine() {
 	w.write("\n")
 }
 
-// write formats the input string and writes it to the buffer.
-func (w *writer) write(s string, a ...interface{}) {
-	w.buf.WriteString(fmt.Sprintf(s, a...))
+// write the input string and writes it to the buffer.
+func (w *writer) write(s string) {
+	w.buf.WriteString(s)
 }
 
-// writeLine writes the formatted string on a newly started line, then terminates
-// the line.
-func (w *writer) writeLine(s string, a ...interface{}) {
+// writeLine writes the string on a newly started line, then terminate the line.
+func (w *writer) writeLine(s string) {
 	if !w.inline {
 		w.startLine()
 	}
-	w.write(s, a...)
+	w.write(s)
 	w.endLine()
 }
 

format/testfiles/test.rego

@@ -53,7 +53,7 @@ fn(x) = y {
 }
 
 long(x) = true {
-    x = "foo"
+    x = "foo %host"
     }
 
     short(x) {

format/testfiles/test.rego.formatted

@@ -58,7 +58,7 @@ fn(x) = y {
 }
 
 long(x) {
-	x = "foo"
+	x = "foo %host"
 }
 
 short(x) {