fast-path.js

"use strict";

const assert = require("assert");
const util = require("./util");
const startsWithNoLookaheadToken = util.startsWithNoLookaheadToken;

function FastPath(value) {
  assert.ok(this instanceof FastPath);
  this.stack = [value];
}

// The name of the current property is always the penultimate element of
// this.stack, and always a String.
FastPath.prototype.getName = function getName() {
  const s = this.stack;
  const len = s.length;
  if (len > 1) {
    return s[len - 2];
  }
  // Since the name is always a string, null is a safe sentinel value to
  // return if we do not know the name of the (root) value.
  /* istanbul ignore next */
  return null;
};

// The value of the current property is always the final element of
// this.stack.
FastPath.prototype.getValue = function getValue() {
  const s = this.stack;
  return s[s.length - 1];
};

function getNodeHelper(path, count) {
  const s = path.stack;

  for (let i = s.length - 1; i >= 0; i -= 2) {
    const value = s[i];

    if (value && !Array.isArray(value) && --count < 0) {
      return value;
    }
  }

  return null;
}

FastPath.prototype.getNode = function getNode(count) {
  return getNodeHelper(this, ~~count);
};

FastPath.prototype.getParentNode = function getParentNode(count) {
  return getNodeHelper(this, ~~count + 1);
};

// Temporarily push properties named by string arguments given after the
// callback function onto this.stack, then call the callback with a
// reference to this (modified) FastPath object. Note that the stack will
// be restored to its original state after the callback is finished, so it
// is probably a mistake to retain a reference to the path.
FastPath.prototype.call = function call(callback /*, name1, name2, ... */) {
  const s = this.stack;
  const origLen = s.length;
  let value = s[origLen - 1];
  const argc = arguments.length;
  for (let i = 1; i < argc; ++i) {
    const name = arguments[i];
    value = value[name];
    s.push(name, value);
  }
  const result = callback(this);
  s.length = origLen;
  return result;
};

// Similar to FastPath.prototype.call, except that the value obtained by
// accessing this.getValue()[name1][name2]... should be array-like. The
// callback will be called with a reference to this path object for each
// element of the array.
FastPath.prototype.each = function each(callback /*, name1, name2, ... */) {
  const s = this.stack;
  const origLen = s.length;
  let value = s[origLen - 1];
  const argc = arguments.length;

  for (let i = 1; i < argc; ++i) {
    const name = arguments[i];
    value = value[name];
    s.push(name, value);
  }

  for (let i = 0; i < value.length; ++i) {
    if (i in value) {
      s.push(i, value[i]);
      // If the callback needs to know the value of i, call
      // path.getName(), assuming path is the parameter name.
      callback(this);
      s.length -= 2;
    }
  }

  s.length = origLen;
};

// Similar to FastPath.prototype.each, except that the results of the
// callback function invocations are stored in an array and returned at
// the end of the iteration.
FastPath.prototype.map = function map(callback /*, name1, name2, ... */) {
  const s = this.stack;
  const origLen = s.length;
  let value = s[origLen - 1];
  const argc = arguments.length;

  for (let i = 1; i < argc; ++i) {
    const name = arguments[i];
    value = value[name];
    s.push(name, value);
  }

  const result = new Array(value.length);

  for (let i = 0; i < value.length; ++i) {
    if (i in value) {
      s.push(i, value[i]);
      result[i] = callback(this, i);
      s.length -= 2;
    }
  }

  s.length = origLen;

  return result;
};

FastPath.prototype.needsParens = function(options) {
  const parent = this.getParentNode();
  if (!parent) {
    return false;
  }

  const name = this.getName();
  const node = this.getNode();

  // If the value of this path is some child of a Node and not a Node
  // itself, then it doesn't need parentheses. Only Node objects (in
  // fact, only Expression nodes) need parentheses.
  if (this.getValue() !== node) {
    return false;
  }

  // Only statements don't need parentheses.
  if (isStatement(node)) {
    return false;
  }

  // Closure compiler requires that type casted expressions to be surrounded by
  // parentheses.
  if (util.hasClosureCompilerTypeCastComment(options.originalText, node)) {
    return true;
  }

  // Identifiers never need parentheses.
  if (node.type === "Identifier") {
    return false;
  }

  if (parent.type === "ParenthesizedExpression") {
    return false;
  }

  // Add parens around the extends clause of a class. It is needed for almost
  // all expressions.
  if (
    (parent.type === "ClassDeclaration" || parent.type === "ClassExpression") &&
    parent.superClass === node &&
    (node.type === "ArrowFunctionExpression" ||
      node.type === "AssignmentExpression" ||
      node.type === "AwaitExpression" ||
      node.type === "BinaryExpression" ||
      node.type === "ConditionalExpression" ||
      node.type === "LogicalExpression" ||
      node.type === "NewExpression" ||
      node.type === "ObjectExpression" ||
      node.type === "ParenthesizedExpression" ||
      node.type === "SequenceExpression" ||
      node.type === "TaggedTemplateExpression" ||
      node.type === "UnaryExpression" ||
      node.type === "UpdateExpression" ||
      node.type === "YieldExpression")
  ) {
    return true;
  }

  if (
    (parent.type === "ArrowFunctionExpression" &&
    parent.body === node &&
    node.type !== "SequenceExpression" && // these have parens added anyway
      startsWithNoLookaheadToken(node, /* forbidFunctionAndClass */ false)) ||
    (parent.type === "ExpressionStatement" &&
      startsWithNoLookaheadToken(node, /* forbidFunctionAndClass */ true))
  ) {
    return true;
  }

  switch (node.type) {
    case "CallExpression": {
      let firstParentNotMemberExpression = parent;
      let i = 0;
      while (
        firstParentNotMemberExpression &&
        firstParentNotMemberExpression.type === "MemberExpression"
      ) {
        firstParentNotMemberExpression = this.getParentNode(++i);
      }

      if (
        firstParentNotMemberExpression.type === "NewExpression" &&
        firstParentNotMemberExpression.callee === this.getParentNode(i - 1)
      ) {
        return true;
      }
      return false;
    }

    case "SpreadElement":
    case "SpreadProperty":
      return (
        parent.type === "MemberExpression" &&
        name === "object" &&
        parent.object === node
      );

    case "UpdateExpression":
      if (parent.type === "UnaryExpression") {
        return (
          node.prefix &&
          ((node.operator === "++" && parent.operator === "+") ||
            (node.operator === "--" && parent.operator === "-"))
        );
      }
    // else fallthrough
    case "UnaryExpression":
      switch (parent.type) {
        case "UnaryExpression":
          return (
            node.operator === parent.operator &&
            (node.operator === "+" || node.operator === "-")
          );

        case "MemberExpression":
          return name === "object" && parent.object === node;

        case "TaggedTemplateExpression":
          return true;

        case "NewExpression":
        case "CallExpression":
          return name === "callee" && parent.callee === node;

        case "BinaryExpression":
          return parent.operator === "**" && name === "left";

        default:
          return false;
      }

    case "BinaryExpression": {
      if (parent.type === "UpdateExpression") {
        return true;
      }

      const isLeftOfAForStatement = node => {
        let i = 0;
        while (node) {
          const parent = this.getParentNode(i++);
          if (!parent) {
            return false;
          }
          if (parent.type === "ForStatement" && parent.init === node) {
            return true;
          }
          node = parent;
        }
        return false;
      };
      if (node.operator === "in" && isLeftOfAForStatement(node)) {
        return true;
      }
    }
    // fallthrough
    case "TSTypeAssertionExpression":
    case "TSAsExpression":
    case "LogicalExpression":
      switch (parent.type) {
        case "ConditionalExpression":
          return node.type === "TSAsExpression";

        case "CallExpression":
        case "NewExpression":
          return name === "callee" && parent.callee === node;

        case "ClassDeclaration":
        case "TSAbstractClassDeclaration":
          return name === "superClass" && parent.superClass === node;
        case "TSTypeAssertionExpression":
        case "TaggedTemplateExpression":
        case "UnaryExpression":
        case "SpreadElement":
        case "SpreadProperty":
        case "ExperimentalSpreadProperty":
        case "BindExpression":
        case "AwaitExpression":
        case "TSAsExpression":
        case "TSNonNullExpression":
          return true;

        case "MemberExpression":
          return name === "object" && parent.object === node;

        case "AssignmentExpression":
          return (
            parent.left === node &&
            (node.type === "TSTypeAssertionExpression" ||
              node.type === "TSAsExpression")
          );
        case "Decorator":
          return (
            parent.expression === node &&
            (node.type === "TSTypeAssertionExpression" ||
              node.type === "TSAsExpression")
          );

        case "BinaryExpression":
        case "LogicalExpression": {
          if (!node.operator && node.type !== "TSTypeAssertionExpression") {
            return true;
          }

          const po = parent.operator;
          const pp = util.getPrecedence(po);
          const no = node.operator;
          const np = util.getPrecedence(no);

          if (pp > np) {
            return true;
          }

          if ((po === "||" || po === "??") && no === "&&") {
            return true;
          }

          if (pp === np && name === "right") {
            assert.strictEqual(parent.right, node);
            return true;
          }

          if (pp === np && !util.shouldFlatten(po, no)) {
            return true;
          }

          // Add parenthesis when working with binary operators
          // It's not stricly needed but helps with code understanding
          if (util.isBitwiseOperator(po)) {
            return true;
          }

          return false;
        }

        default:
          return false;
      }

    case "TSParenthesizedType": {
      const grandParent = this.getParentNode(1);
      if (
        (parent.type === "TypeParameter" ||
          parent.type === "VariableDeclarator" ||
          parent.type === "TypeAnnotation" ||
          parent.type === "GenericTypeAnnotation" ||
          parent.type === "TSTypeReference") &&
        (node.typeAnnotation.type === "TypeAnnotation" &&
          node.typeAnnotation.typeAnnotation.type !== "TSFunctionType" &&
          grandParent.type !== "TSTypeOperator")
      ) {
        return false;
      }
      // Delegate to inner TSParenthesizedType
      if (node.typeAnnotation.type === "TSParenthesizedType") {
        return false;
      }
      return true;
    }

    case "SequenceExpression":
      switch (parent.type) {
        case "ReturnStatement":
          return false;

        case "ForStatement":
          // Although parentheses wouldn't hurt around sequence
          // expressions in the head of for loops, traditional style
          // dictates that e.g. i++, j++ should not be wrapped with
          // parentheses.
          return false;

        case "ExpressionStatement":
          return name !== "expression";

        case "ArrowFunctionExpression":
          // We do need parentheses, but SequenceExpressions are handled
          // specially when printing bodies of arrow functions.
          return name !== "body";

        default:
          // Otherwise err on the side of overparenthesization, adding
          // explicit exceptions above if this proves overzealous.
          return true;
      }

    case "YieldExpression":
      if (
        parent.type === "UnaryExpression" ||
        parent.type === "AwaitExpression" ||
        parent.type === "TSAsExpression" ||
        parent.type === "TSNonNullExpression"
      ) {
        return true;
      }
    // else fallthrough
    case "AwaitExpression":
      switch (parent.type) {
        case "TaggedTemplateExpression":
        case "BinaryExpression":
        case "LogicalExpression":
        case "SpreadElement":
        case "SpreadProperty":
        case "TSAsExpression":
        case "TSNonNullExpression":
          return true;

        case "MemberExpression":
          return parent.object === node;

        case "NewExpression":
        case "CallExpression":
          return parent.callee === node;

        case "ConditionalExpression":
          return parent.test === node;

        default:
          return false;
      }

    case "ArrayTypeAnnotation":
      return parent.type === "NullableTypeAnnotation";

    case "IntersectionTypeAnnotation":
    case "UnionTypeAnnotation":
      return (
        parent.type === "ArrayTypeAnnotation" ||
        parent.type === "NullableTypeAnnotation" ||
        parent.type === "IntersectionTypeAnnotation" ||
        parent.type === "UnionTypeAnnotation"
      );

    case "NullableTypeAnnotation":
      return parent.type === "ArrayTypeAnnotation";

    case "FunctionTypeAnnotation":
      return (
        parent.type === "UnionTypeAnnotation" ||
        parent.type === "IntersectionTypeAnnotation" ||
        parent.type === "ArrayTypeAnnotation"
      );

    case "StringLiteral":
    case "NumericLiteral":
    case "Literal":
      if (
        typeof node.value === "string" &&
        parent.type === "ExpressionStatement" &&
        // TypeScript workaround for eslint/typescript-eslint-parser#267
        // See corresponding workaround in printer.js case: "Literal"
        ((options.parser !== "typescript" && !parent.directive) ||
          (options.parser === "typescript" &&
            options.originalText.substr(util.locStart(node) - 1, 1) === "("))
      ) {
        // To avoid becoming a directive
        const grandParent = this.getParentNode(1);

        return (
          grandParent.type === "Program" ||
          grandParent.type === "BlockStatement"
        );
      }

      return (
        parent.type === "MemberExpression" &&
        typeof node.value === "number" &&
        name === "object" &&
        parent.object === node
      );

    case "AssignmentExpression": {
      const grandParent = this.getParentNode(1);

      if (parent.type === "ArrowFunctionExpression" && parent.body === node) {
        return true;
      } else if (
        parent.type === "ClassProperty" &&
        parent.key === node &&
        parent.computed
      ) {
        return false;
      } else if (
        parent.type === "TSPropertySignature" &&
        parent.name === node
      ) {
        return false;
      } else if (
        parent.type === "ForStatement" &&
        (parent.init === node || parent.update === node)
      ) {
        return false;
      } else if (parent.type === "ExpressionStatement") {
        return node.left.type === "ObjectPattern";
      } else if (parent.type === "TSPropertySignature" && parent.key === node) {
        return false;
      } else if (parent.type === "AssignmentExpression") {
        return false;
      } else if (
        parent.type === "SequenceExpression" &&
        grandParent &&
        grandParent.type === "ForStatement" &&
        (grandParent.init === parent || grandParent.update === parent)
      ) {
        return false;
      }
      return true;
    }
    case "ConditionalExpression":
      switch (parent.type) {
        case "TaggedTemplateExpression":
        case "UnaryExpression":
        case "SpreadElement":
        case "SpreadProperty":
        case "BinaryExpression":
        case "LogicalExpression":
        case "ExportDefaultDeclaration":
        case "AwaitExpression":
        case "JSXSpreadAttribute":
        case "TSTypeAssertionExpression":
        case "TSAsExpression":
        case "TSNonNullExpression":
          return true;

        case "NewExpression":
        case "CallExpression":
          return name === "callee" && parent.callee === node;

        case "ConditionalExpression":
          return name === "test" && parent.test === node;

        case "MemberExpression":
          return name === "object" && parent.object === node;

        default:
          return false;
      }

    case "FunctionExpression":
      switch (parent.type) {
        case "CallExpression":
          return name === "callee"; // Not strictly necessary, but it's clearer to the reader if IIFEs are wrapped in parentheses.
        case "TaggedTemplateExpression":
          return true; // This is basically a kind of IIFE.
        case "ExportDefaultDeclaration":
          return true;
        default:
          return false;
      }

    case "ArrowFunctionExpression":
      switch (parent.type) {
        case "CallExpression":
          return name === "callee";

        case "NewExpression":
          return name === "callee";

        case "MemberExpression":
          return name === "object";

        case "TSAsExpression":
        case "BindExpression":
        case "TaggedTemplateExpression":
        case "UnaryExpression":
        case "LogicalExpression":
        case "BinaryExpression":
        case "AwaitExpression":
        case "TSTypeAssertionExpression":
          return true;

        case "ConditionalExpression":
          return name === "test";

        default:
          return false;
      }

    case "ClassExpression":
      return parent.type === "ExportDefaultDeclaration";
  }

  return false;
};

function isStatement(node) {
  return (
    node.type === "BlockStatement" ||
    node.type === "BreakStatement" ||
    node.type === "ClassBody" ||
    node.type === "ClassDeclaration" ||
    node.type === "ClassMethod" ||
    node.type === "ClassProperty" ||
    node.type === "ClassPrivateProperty" ||
    node.type === "ContinueStatement" ||
    node.type === "DebuggerStatement" ||
    node.type === "DeclareClass" ||
    node.type === "DeclareExportAllDeclaration" ||
    node.type === "DeclareExportDeclaration" ||
    node.type === "DeclareFunction" ||
    node.type === "DeclareInterface" ||
    node.type === "DeclareModule" ||
    node.type === "DeclareModuleExports" ||
    node.type === "DeclareVariable" ||
    node.type === "DoWhileStatement" ||
    node.type === "ExportAllDeclaration" ||
    node.type === "ExportDefaultDeclaration" ||
    node.type === "ExportNamedDeclaration" ||
    node.type === "ExpressionStatement" ||
    node.type === "ForAwaitStatement" ||
    node.type === "ForInStatement" ||
    node.type === "ForOfStatement" ||
    node.type === "ForStatement" ||
    node.type === "FunctionDeclaration" ||
    node.type === "IfStatement" ||
    node.type === "ImportDeclaration" ||
    node.type === "InterfaceDeclaration" ||
    node.type === "LabeledStatement" ||
    node.type === "MethodDefinition" ||
    node.type === "ReturnStatement" ||
    node.type === "SwitchStatement" ||
    node.type === "ThrowStatement" ||
    node.type === "TryStatement" ||
    node.type === "TSAbstractClassDeclaration" ||
    node.type === "TSEnumDeclaration" ||
    node.type === "TSImportEqualsDeclaration" ||
    node.type === "TSInterfaceDeclaration" ||
    node.type === "TSModuleDeclaration" ||
    node.type === "TSNamespaceExportDeclaration" ||
    node.type === "TSNamespaceFunctionDeclaration" ||
    node.type === "TypeAlias" ||
    node.type === "VariableDeclaration" ||
    node.type === "WhileStatement" ||
    node.type === "WithStatement"
  );
}

module.exports = FastPath;