lezer-template-plaintext

A Lezer grammar for parsing template plaintext (plaintext with {{variable}} holes) with incremental parsing support and TypeScript definitions.

Install

npm i lezer-template-plaintext

Features

• Parse free-form plaintext with {{variable}} holes
• Backslash escapes for {, }, and \\ both in text and inside variables
• Incremental parsing ready for editors

Usage

Basic

import { parser } from "lezer-template-plaintext";

const tree = parser.parse(
  "Hello \\{world\\} and {{name}}! \{\{ not a variable"
);
console.log(tree.toString());

With CodeMirror

import {
  parser,
  templatePlaintextHighlighting,
} from "lezer-template-plaintext";
import { LRLanguage } from "@codemirror/language";
import { HighlightStyle, syntaxHighlighting } from "@codemirror/language";

const templatePlaintextLanguage = LRLanguage.define({
  parser,
  languageData: { name: "template-plaintext" },
});

const highlightStyle = HighlightStyle.define([templatePlaintextHighlighting]);
const extensions = [
  templatePlaintextLanguage,
  syntaxHighlighting(highlightStyle),
];

Tree Navigation

import { parser } from "lezer-template-plaintext";
import * as terms from "lezer-template-plaintext";

const tree = parser.parse("Hi {{first}} {{last}}! \{escaped\}");
const cursor = tree.cursor();
do {
  if (cursor.type.id === terms.Variable) {
    console.log("Found variable at:", cursor.from, cursor.to);
  }
} while (cursor.next());

Error Handling

import { parser } from "lezer-template-plaintext";

function parseWithErrors(pattern: string) {
  const tree = parser.parse(pattern);
  const errors: { from: number; to: number; message: string }[] = [];

  tree.iterate({
    enter: (node) => {
      if (node.type.isError) {
        errors.push({
          from: node.from,
          to: node.to,
          message: `Syntax error at ${node.from}-${node.to}`,
        });
      }
    },
  });

  return { tree, errors };
}

API

Exports

• parser - Lezer parser instance
• templatePlaintextHighlighting - CodeMirror syntax highlighting
• Grammar terms - Node type constants for tree navigation (e.g. Variable)

Types

parser.parse(input: string, fragments?: TreeFragment[], ranges?: {from: number, to: number}[]): Tree

Development

git clone https://github.com/Sec-ant/lezer-template-plaintext
cd lezer-template-plaintext
pnpm install
pnpm build
pnpm test

Commands:

• pnpm test:run - Run all tests
• pnpm test:ui - Interactive test UI

Contributing

1. Fork the repository
2. Create a feature branch
3. Add tests in tests/fixtures/
4. Ensure tests pass
5. Submit a pull request

License

MIT