feat: preserve original formatting, maintaining things like comments …

…in the generated dockerfile (#9)

cmd/anchor/root.go

@@ -89,20 +89,32 @@ var rootCmd = &cobra.Command{
 		}
 		appendArch := len(options.Architectures) > 1
 
+		content, err := os.Open(options.InputFile)
+		if err != nil {
+			return err
+		}
+		defer content.Close()
+		lines := []string{}
+		scanner := bufio.NewScanner(content)
+		for scanner.Scan() {
+			lines = append(lines, scanner.Text())
+		}
+
+		if err := scanner.Err(); err != nil {
+			return err
+		}
 		for _, architecture := range options.Architectures {
 			content, err := os.Open(options.InputFile)
 			if err != nil {
 				return err
 			}
-
 			defer content.Close()
 			result, err := parser.Parse(content)
 			if err != nil {
 				return err
 			}
 
 			node := result.AST
-			anchor.PrintNode(node)
 
 			color.Cyan("Anchoring to architecture: %s\n", architecture)
 			image := ""
@@ -112,7 +124,7 @@ var rootCmd = &cobra.Command{
 			}
 
 			var builder strings.Builder
-			anchor.WriteDockerfile(&builder, node, true)
+			anchor.WriteDockerfile(&builder, node, true, 0, lines)
 			outputName := options.OutputFile
 			if appendArch {
 				outputName = fmt.Sprintf("%s.%s", outputName, architecture)

docker.go

@@ -29,7 +29,19 @@ func attachDockerSha(node *parser.Node) (string, error) {
 	return node.Value, nil
 }
 
-func WriteDockerfile(builder *strings.Builder, node *parser.Node, useOriginal bool) {
+func WriteDockerfile(builder *strings.Builder, node *parser.Node, useOriginal bool, currentLine int, lines []string) int {
+	// this allows us to maintain things like comments and newlines in the original Dockerfile
+	if currentLine != 0 && node.StartLine != 0 && currentLine < node.StartLine {
+		for i := currentLine + 1; i < node.StartLine; i++ {
+			builder.WriteString(lines[i-1])
+			builder.WriteString("\n")
+		}
+	}
+	if currentLine == 0 {
+		currentLine = 1
+	} else if node.EndLine != 0 {
+		currentLine = node.EndLine
+	}
 	if node.Value == "FROM" || node.Value == "RUN" {
 		useOriginal = false
 	}
@@ -47,24 +59,15 @@ func WriteDockerfile(builder *strings.Builder, node *parser.Node, useOriginal bo
 		builder.WriteString(s)
 	}
 	for _, child := range node.Children {
-		WriteDockerfile(builder, child, useOriginal)
-		builder.WriteString("\n\n")
+		currentLine = WriteDockerfile(builder, child, useOriginal, currentLine, lines)
+		builder.WriteString("\n")
 	}
 
 	if node.Next != nil {
 		builder.WriteString(" ")
-		WriteDockerfile(builder, node.Next, useOriginal)
-	}
-}
-
-func PrintNode(node *parser.Node) {
-	for _, child := range node.Children {
-		PrintNode(child)
-	}
-
-	if node.Next != nil {
-		PrintNode(node.Next)
+		currentLine = WriteDockerfile(builder, node.Next, useOriginal, currentLine, lines)
 	}
+	return currentLine
 }
 
 func ParseNode(ctx context.Context, node *parser.Node, architecture string, image *string) error {