TxtAST Interface

TxtAST define AST(Abstract Syntax Tree) for processing in textlint.

What is AST?

Abstract syntax tree is a tree representation of the abstract syntactic structure of text.

textlint's plugin parse text to AST. AST is a tree structure that is consist of Txt{{Type}}Node like TxtParagraphNode. Each node has common properties like type, raw, loc, range and parent that is defined in TxtNode interface.

Each node has own properties that is defined in each node type.

AST explorer for textlint is useful for understanding AST.

`TxtNode`

TxtNode is an abstract node.

/**
 * Basic TxtNode
 * Probably, Real TxtNode implementation has more properties.
 */
interface TxtNode {
    type: string;
    raw: string;
    range: TxtNodeRange;
    loc: TxtNodeLineLocation;
    // parent is runtime information
    // Not need in AST
    // For example, top Root Node like `Document` has not parent.
    parent?: TxtNode;
}


/**
 * Location
 */
interface TxtNodeLineLocation {
    start: TxtNodePosition;
    end: TxtNodePosition;
}

/**
 * Position's line start with 1.
 * Position's column start with 0.
 * This is for compatibility with JavaScript AST.
 * https://gist.github.com/azu/8866b2cb9b7a933e01fe
 */
interface TxtNodePosition {
    line: number; // start with 1
    column: number; // start with 0
}

/**
 * Range start with 0
 */
export type TxtNodeRange = readonly [startIndex: number, endIndex: number];

TxtNode must have these properties.

type: type of Node
raw: raw value of Node
- if you want to get raw value, please use getSource(<node>) instead of it..
loc: location object
range: location info array like [startIndex, endIndex]
parent: (optional) parent node of this node.
- It is attached in runtime
- Parser user ignore this property

`TxtTextNode`

TxtTextNode is an abstract node that inherit TxtNode interface.

/**
 * Text Node.
 * Text Node has inline value.
 * For example, `Str` Node is a TxtTextNode.
 */
interface TxtTextNode extends TxtNode {
    value: string;
}

TxtTextNode must have these properties.

value: the value of inline node.

Example: Str node is a TxtTextNode.

`TxtParentNode`

TxtParentNode is an abstract node that inherit TxtNode interface.

/**
 * Parent Node.
 * Parent Node has children that are consist of TxtNode or TxtTextNode
 */
interface TxtParentNode extends TxtNode {
    children: Array<TxtNode | TxtTextNode>;
}

TxtParentNode must have these properties.

children: child nodes of this node.

Example: Paragraph node is a TxtParentNode.

`type`

type is TxtNode type.

All Types are defined in @textlint/ast-node-types. You can use this ASTNodeTypes value via following way:

import { ASTNodeTypes } from "@textlint/ast-node-types";

console.log(ASTNodeTypes.Str); // "Str"

You can get Node type for Type name by TypeofTxtNode in TypeScript.

// In TypeScript
import { ASTNodeTypes } from "@textlint/ast-node-types";

const nodeType = TypeofTxtNode<ASTNodeTypes.Str>; // TxtTextNode

All node types

These types are defined in @textlint/ast-node-types.

Type name	Node type	Description
ASTNodeTypes.Document	TxtDocumentNode(TxtParentNode)	Root Node
ASTNodeTypes.DocumentExit	TxtDocumentNode(TxtParentNode)
ASTNodeTypes.Paragraph	TxtParagraphNode(TxtParentNode)	Paragraph Node
ASTNodeTypes.ParagraphExit	TxtParagraphNode(TxtParentNode)
ASTNodeTypes.BlockQuote	TxtBlockQuoteNode(TxtParentNode)	> Block Quote Node
ASTNodeTypes.BlockQuoteExit	TxtBlockQuoteNode(TxtParentNode)
ASTNodeTypes.List	TxtListNode(TxtParentNode)	List Node
ASTNodeTypes.ListExit	TxtListNode(TxtParentNode)
ASTNodeTypes.ListItem	TxtListItemNode(TxtParentNode)	List (each) item Node
ASTNodeTypes.ListItemExit	TxtListItemNode(TxtParentNode)
ASTNodeTypes.Header	TxtHeaderNode(TxtParentNode)	# Header Node
ASTNodeTypes.HeaderExit	TxtHeaderNode(TxtParentNode)
ASTNodeTypes.CodeBlock	TxtCodeBlockNode	Code Block Node
ASTNodeTypes.CodeBlockExit	TxtCodeBlockNode
ASTNodeTypes.HtmlBlock	TxtHtmlBlockNode(TxtParentNode)	HTML Block Node
ASTNodeTypes.HtmlBlockExit	TxtHtmlBlockNode(TxtParentNode)
ASTNodeTypes.Link	TxtLinkNode(TxtParentNode)	Link Node
ASTNodeTypes.LinkExit	TxtLinkNode(TxtParentNode)
ASTNodeTypes.LinkReference	TxtLinkReferenceNode(TxtParentNode)	Link Reference Node(`[link][1]`)
ASTNodeTypes.LinkReferenceExit	TxtLinkReferenceNode(TxtParentNode)
ASTNodeTypes.Delete	TxtDeleteNode(TxtParentNode)	Delete Node(`~Str~`)
ASTNodeTypes.DeleteExit	TxtDeleteNode(TxtParentNode)
ASTNodeTypes.Emphasis	TxtEmphasisNode(TxtParentNode)	Emphasis(`Str`)
ASTNodeTypes.EmphasisExit	TxtEmphasisNode(TxtParentNode)
ASTNodeTypes.Strong	TxtStrongNode(TxtParentNode)	Strong Node(`Str`)
ASTNodeTypes.StrongExit	TxtStrongNode(TxtParentNode)
ASTNodeTypes.Break	TxtBreakNode	Hard Break Node(`Str<space><space>`)
ASTNodeTypes.BreakExit	TxtBreakNode
ASTNodeTypes.Image	TxtImageNode	Image Node
ASTNodeTypes.ImageExit	TxtImageNode
ASTNodeTypes.ImageReference	TxtImageReferenceNode	Image Reference Node(`![alt][1]`)
ASTNodeTypes.ImageReferenceExit	TxtImageReferenceNode
ASTNodeTypes.Definition	TxtDefinitionNode	Definition Node(`[1]: https://example.com`)
ASTNodeTypes.DefinitionExit	TxtDefinitionNode
ASTNodeTypes.HorizontalRule	TxtHorizontalRuleNode	Horizontal Node(`---`)
ASTNodeTypes.HorizontalRuleExit	TxtHorizontalRuleNode
ASTNodeTypes.Comment	TxtCommentNode	Comment Node
ASTNodeTypes.CommentExit	TxtCommentNode
ASTNodeTypes.Str	TxtStrNode	Str Node
ASTNodeTypes.StrExit	TxtStrNode
ASTNodeTypes.Code	TxtCodeNode	Inline Code Node
ASTNodeTypes.CodeExit	TxtCodeNode
ASTNodeTypes.Html	TxtHtmlNode	Inline HTML Node
ASTNodeTypes.HtmlExit	TxtHtmlNode
ASTNodeTypes.Table	TxtTableNode	Table Node. textlint 13+
ASTNodeTypes.TableExit	TxtTableNode
ASTNodeTypes.TableRow	TxtTableRowNode	Table row Node. textlint 13+
ASTNodeTypes.TableRowExit	TxtTableRowNode
ASTNodeTypes.TableCell	TxtTableCellNode	Table cell Node. textlint 13+
ASTNodeTypes.TableCellExit	TxtTableCellNode

📝Note LinkReference, ImageReference and Definition are introduced in textlint v14.5.0.

Some node have additional properties. For example, TxtHeaderNode has level property.

export interface TxtHeaderNode extends TxtParentNode {
    type: "Header";
    depth: 1 | 2 | 3 | 4 | 5 | 6;
    children: PhrasingContent[];
}

For more details, see @textlint/ast-node-types.

@textlint/ast-node-types/src/NodeType.ts.

These type are based on HTML tag and Markdown syntax. Other plugin has defined other node type that is not defined in @textlint/ast-node-types, but you can specify it as just a string.

// A rule can treat "Example" node type
export default () => {
    return {
        ["Example"](node) {
            // do something
        }
    };
};

Minimal node property

TxtAST allow to extend node property. But, Following node should have some properties.

`Header`

depth: level of header
- Example: <h1> is depth:1, <h2> is depth:2...

`Link`

url: link url

`Image`

url: image url

Built-in Parser

textlint has built-in parsers.

Package	Version	Description
`@textlint/markdown-to-ast`		markdown parser
`@textlint/text-to-ast`		plain text parser

If you want to get other type, please create new issue.

Package

That TxtNode interface is defined in packages/ast-node-types.

If you want to use this interface from TypeScript, packages/ast-node-types is useful.

Online Parsing Demo

AST explorer for textlint is useful for understanding AST.

Minimum(recommended) rules is following code:

/**
 * @param {RuleContext} context
 */
export default function(context) {
    const { Syntax } = context;
    // root object
    return {
        [Syntax.Document](node) {
        },
        [Syntax.Paragraph](node) {
        },
        [Syntax.Str](node) {
        }
    };
}

`loc`

loc is location info object.

{
  "loc": {
    "start": {
      "line": 2,
      "column": 4
    },
    "end": {
      "line": 2,
      "column": 10
    }
  }
}

line of location start with 1 (1-indexed).
column of location start with 0 (0-indexed).

This is for compatibility with JavaScript AST.

Why do line of location in JavaScript AST(ESTree) start with 1 and not 0?

Important Note:

Text -> AST TxtNode(0-based columns here) -> textlint -> TextLintMessage(1-based columns)

TxtNode has 0-based columns, but the result of linting named TextLintMessage has 1-based columns.

In other word, textlint's rule handle TxtNode, but formatter handle TextLintMessage.

Example

Input: *text*

Output: The AST by AST explorer for textlint + Markdown

{
  "type": "Document",
  "children": [
    {
      "type": "Paragraph",
      "children": [
        {
          "type": "Emphasis",
          "children": [
            {
              "type": "Str",
              "value": "text",
              "loc": {
                "start": {
                  "line": 1,
                  "column": 1
                },
                "end": {
                  "line": 1,
                  "column": 5
                }
              },
              "range": [
                1,
                5
              ],
              "raw": "text"
            }
          ],
          "loc": {
            "start": {
              "line": 1,
              "column": 0
            },
            "end": {
              "line": 1,
              "column": 6
            }
          },
          "range": [
            0,
            6
          ],
          "raw": "*text*"
        }
      ],
      "loc": {
        "start": {
          "line": 1,
          "column": 0
        },
        "end": {
          "line": 1,
          "column": 6
        }
      },
      "range": [
        0,
        6
      ],
      "raw": "*text*"
    }
  ],
  "loc": {
    "start": {
      "line": 1,
      "column": 0
    },
    "end": {
      "line": 1,
      "column": 6
    }
  },
  "range": [
    0,
    6
  ],
  "raw": "*text*"
}

Illustration

          *   text   *
          |   |__|   |
          |   value  |
          |__________|
               raw

Document is a TxtParentNode and type is Document
- have children, but not have value
Paragraph is a TxtParentNode and type is Paragraph
- have children, but not have value
Emphasis is a TxtTextNode and type is Emphasis
- have value
"text" is a TxtTextNode and type is Str
- have value

Unist

TxtAST have a minimum of compatibility for unist: Universal Syntax Tree.

We have discussed Unist in Compliances tests for TxtNode #141.

For testing Processor plugin

You can use @textlint/ast-tester for testing your processor plugin's parser.

textlint/@textlint/ast-tester: Compliance tests for textlint's AST

import { test, isTxtAST } from "@textlint/ast-tester";
// your implement
import yourParse from "your-parser";
// recommenced: test much pattern test
const AST = yourParse("This is text");

// Validate AST
test(AST); // if the AST is invalid, then throw Error

isTxtAST(AST); // true or false

⚠️ Current test function does not check node specific properties. For example, TxtHeaderNode has level property, but test function does not check it.

Issue: ast-tester should validate individual Node type · Issue #1009 · textlint/textlint

What is AST?​

TxtNode​

TxtTextNode​

TxtParentNode​

type​

All node types​

Minimal node property​

Header​

Link​

Image​

Built-in Parser​

Package​

Online Parsing Demo​

loc​

Example​

Unist​

For testing Processor plugin​