Refactor the writer functionality into a package (#22)

* Refactoring the writer into a package

* Fixing things up and trimming some fat

e2e_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/unmango/go-make"
 	"github.com/unmango/go-make/printer"
 	"github.com/unmango/go-make/token"
+	"github.com/unmango/go-make/writer"
 )
 
 //go:embed testdata
@@ -58,7 +59,7 @@ var _ = Describe("E2E", func() {
 			Expect(err).NotTo(HaveOccurred())
 
 			buf := &bytes.Buffer{}
-			w := make.NewWriter(buf)
+			w := writer.New(buf)
 
 			Expect(printer.Fprint(w, f)).To(BeNumerically(">", 0))
 			Expect(buf.String()).To(Equal(input))

printer/printer.go

@@ -106,6 +106,10 @@ func (p *printer) recipeList(l []*ast.Recipe) {
 }
 
 func (p *printer) rule(r *ast.Rule) {
+	if r == nil {
+		return
+	}
+
 	p.targetList(r.Targets)
 	fillSpace(p, r.Colon)
 	p.tok(p.posFor(r.Colon), token.COLON)
@@ -118,6 +122,10 @@ func (p *printer) rule(r *ast.Rule) {
 }
 
 func (p *printer) variable(v *ast.Variable) {
+	if v == nil {
+		return
+	}
+
 	p.expr(v.Name)
 	fillSpace(p, v.OpPos)
 	p.tok(p.posFor(v.OpPos), v.Op)
@@ -143,7 +151,9 @@ func (p *printer) declList(l []ast.Decl) {
 }
 
 func (p *printer) file(file *ast.File) {
-	p.declList(file.Decls)
+	if file != nil {
+		p.declList(file.Decls)
+	}
 }
 
 func (p *printer) printNode(node any) error {