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Printer: Implement Indentation Printer (#1300)
This pull request implements a new `IndentPrinter` class in the `@herb-tools/printer` package that can be used to print an AST and preserve all content as-is while replacing leading whitespace on each line with the correct indentation based on the AST nesting depth. Example: ```html <div> <ul> <li> Hello </li> </ul> </div> ``` Becomes: ```html <div> <ul> <li> Hello </li> </ul> </div> ``` This is going to be useful when changing the nodes hierarchy in the AST and want the indentation to be reflected based on that transformation without needing to fully format it. Especially for things like the autofix for the `erb-no-duplicate-branch-elements` linter rule in #1301.
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‎javascript/packages/printer/src/indent-printer.ts‎

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import { IdentityPrinter } from "./identity-printer.js"
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import type * as Nodes from "@herb-tools/core"
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/**
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* IndentPrinter - Re-indentation printer that preserves content but adjusts indentation
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*
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* Extends IdentityPrinter to preserve all content as-is while replacing
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* leading whitespace on each line with the correct indentation based on
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* the AST nesting depth.
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*/
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export class IndentPrinter extends IdentityPrinter {
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protected indentLevel: number = 0
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protected indentWidth: number
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private pendingIndent: boolean = false
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constructor(indentWidth: number = 2) {
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super()
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this.indentWidth = indentWidth
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}
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protected get indent(): string {
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return " ".repeat(this.indentLevel * this.indentWidth)
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}
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protected write(content: string): void {
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if (this.pendingIndent && content.length > 0) {
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this.pendingIndent = false
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this.context.write(this.indent + content)
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} else {
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this.context.write(content)
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}
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}
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visitLiteralNode(node: Nodes.LiteralNode): void {
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this.writeWithIndent(node.content)
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}
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visitHTMLTextNode(node: Nodes.HTMLTextNode): void {
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this.writeWithIndent(node.content)
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}
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visitHTMLElementNode(node: Nodes.HTMLElementNode): void {
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const tagName = node.tag_name?.value
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if (tagName) {
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this.context.enterTag(tagName)
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}
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if (node.open_tag) {
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this.visit(node.open_tag)
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}
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if (node.body) {
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this.indentLevel++
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node.body.forEach(child => this.visit(child))
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this.indentLevel--
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}
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if (node.close_tag) {
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this.visit(node.close_tag)
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}
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if (tagName) {
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this.context.exitTag()
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}
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}
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visitERBIfNode(node: Nodes.ERBIfNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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if (node.subsequent) {
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this.visit(node.subsequent)
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}
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if (node.end_node) {
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this.visit(node.end_node)
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}
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}
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visitERBElseNode(node: Nodes.ERBElseNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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}
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visitERBBlockNode(node: Nodes.ERBBlockNode): void {
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this.printERBNode(node)
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if (node.body) {
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this.indentLevel++
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node.body.forEach(child => this.visit(child))
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this.indentLevel--
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}
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if (node.end_node) {
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this.visit(node.end_node)
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}
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}
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visitERBCaseNode(node: Nodes.ERBCaseNode): void {
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this.printERBNode(node)
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if (node.children) {
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this.indentLevel++
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node.children.forEach(child => this.visit(child))
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this.indentLevel--
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}
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if (node.conditions) {
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this.indentLevel++
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node.conditions.forEach(condition => this.visit(condition))
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this.indentLevel--
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}
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if (node.else_clause) {
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this.indentLevel++
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this.visit(node.else_clause)
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this.indentLevel--
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}
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if (node.end_node) {
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this.visit(node.end_node)
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}
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}
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visitERBWhenNode(node: Nodes.ERBWhenNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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}
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visitERBWhileNode(node: Nodes.ERBWhileNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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if (node.end_node) {
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this.visit(node.end_node)
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}
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}
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visitERBUntilNode(node: Nodes.ERBUntilNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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if (node.end_node) {
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this.visit(node.end_node)
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}
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}
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visitERBForNode(node: Nodes.ERBForNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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if (node.end_node) {
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this.visit(node.end_node)
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}
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}
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visitERBBeginNode(node: Nodes.ERBBeginNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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if (node.rescue_clause) {
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this.visit(node.rescue_clause)
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}
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if (node.else_clause) {
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this.visit(node.else_clause)
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}
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if (node.ensure_clause) {
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this.visit(node.ensure_clause)
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}
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if (node.end_node) {
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this.visit(node.end_node)
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}
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}
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visitERBRescueNode(node: Nodes.ERBRescueNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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if (node.subsequent) {
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this.visit(node.subsequent)
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}
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}
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visitERBEnsureNode(node: Nodes.ERBEnsureNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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}
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visitERBUnlessNode(node: Nodes.ERBUnlessNode): void {
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this.printERBNode(node)
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if (node.statements) {
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this.indentLevel++
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node.statements.forEach(statement => this.visit(statement))
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this.indentLevel--
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}
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if (node.else_clause) {
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this.visit(node.else_clause)
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}
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if (node.end_node) {
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this.visit(node.end_node)
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}
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}
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/**
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* Write content, replacing leading whitespace on each line with the current indent.
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*
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* Uses a pendingIndent mechanism: when content ends with a newline followed by
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* whitespace-only, sets pendingIndent=true instead of writing the indent immediately.
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* The indent is then applied at the correct level when the next node writes content
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* (via the overridden write() method).
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*/
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protected writeWithIndent(content: string): void {
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if (!content.includes("\n")) {
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if (this.pendingIndent) {
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this.pendingIndent = false
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const trimmed = content.replace(/^[ \t]+/, "")
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if (trimmed.length > 0) {
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this.context.write(this.indent + trimmed)
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}
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} else {
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this.context.write(content)
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}
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return
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}
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const lines = content.split("\n")
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const lastIndex = lines.length - 1
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for (let i = 0; i < lines.length; i++) {
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if (i > 0) {
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this.context.write("\n")
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}
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const line = lines[i]
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const trimmed = line.replace(/^[ \t]+/, "")
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if (i === 0) {
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if (this.pendingIndent) {
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this.pendingIndent = false
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if (trimmed.length > 0) {
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this.context.write(this.indent + trimmed)
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}
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} else {
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this.context.write(line)
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}
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} else if (i === lastIndex && trimmed.length === 0) {
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this.pendingIndent = true
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} else if (trimmed.length === 0) {
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// Middle whitespace-only line: write nothing (newline already written above)
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} else {
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this.context.write(this.indent + trimmed)
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}
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}
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}
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}

‎javascript/packages/printer/src/index.ts‎

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export { IdentityPrinter } from "./identity-printer.js"
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export { IndentPrinter } from "./indent-printer.js"
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export { ERBToRubyStringPrinter } from "./erb-to-ruby-string-printer.js"
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export { PrintContext } from "./print-context.js"
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export { Printer, DEFAULT_PRINT_OPTIONS } from "./printer.js"

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