yarn-spinner-runner-ts/dist/parse/lexer.js

TypeScript parser, compiler, and runtime for Yarn Spinner 3.x with React adapter [NPM package](https://www.npmjs.com/package/yarn-spinner-runner-ts)

// Minimal indentation-sensitive lexer to support options and their bodies.
export function lex(input) {
    const lines = input.replace(/\r\n?/g, "\n").split("\n");
    const tokens = [];
    const indentStack = [0];
    let inHeaders = true;
    function push(type, text, line, column) {
        tokens.push({ type, text, line, column });
    }
    for (let i = 0; i < lines.length; i++) {
        const raw = lines[i];
        const lineNum = i + 1;
        const indent = raw.match(/^[ \t]*/)?.[0] ?? "";
        const content = raw.slice(indent.length);
        if (content.trim() === "") {
            push("EMPTY", "", lineNum, 1);
            continue;
        }
        // Manage indentation tokens only within node bodies and on non-empty lines
        if (!inHeaders) {
            const prev = indentStack[indentStack.length - 1];
            if (indent.length > prev) {
                indentStack.push(indent.length);
                push("INDENT", "", lineNum, 1);
            }
            else if (indent.length < prev) {
                while (indentStack.length && indent.length < indentStack[indentStack.length - 1]) {
                    indentStack.pop();
                    push("DEDENT", "", lineNum, 1);
                }
            }
        }
        if (content === "---") {
            inHeaders = false;
            push("NODE_START", content, lineNum, indent.length + 1);
            continue;
        }
        if (content === "===") {
            inHeaders = true;
            // flush indentation to root
            while (indentStack.length > 1) {
                indentStack.pop();
                push("DEDENT", "", lineNum, 1);
            }
            push("NODE_END", content, lineNum, indent.length + 1);
            continue;
        }
        // Header: key: value (only valid while inHeaders)
        if (inHeaders) {
            const m = content.match(/^([A-Za-z_][A-Za-z0-9_]*)\s*:\s*(.*)$/);
            if (m) {
                push("HEADER_KEY", m[1], lineNum, indent.length + 1);
                push("HEADER_VALUE", m[2], lineNum, indent.length + 1 + m[0].indexOf(m[2]));
                continue;
            }
        }
        if (content.startsWith("->")) {
            push("OPTION", content.slice(2).trim(), lineNum, indent.length + 1);
            continue;
        }
        // Commands like <<...>> (single line)
        const cmd = content.match(/^<<(.+?)>>\s*$/);
        if (cmd) {
            push("COMMAND", cmd[1].trim(), lineNum, indent.length + 1);
            continue;
        }
        // Plain text line
        push("TEXT", content, lineNum, indent.length + 1);
    }
    // close remaining indentation at EOF
    while (indentStack.length > 1) {
        indentStack.pop();
        tokens.push({ type: "DEDENT", text: "", line: lines.length, column: 1 });
    }
    tokens.push({ type: "EOF", text: "", line: lines.length + 1, column: 1 });
    return tokens;
}
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