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/**
* @fileoverview A rule to disallow using `this`/`super` before `super()`.
* @author Toru Nagashima
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("../util/ast-utils");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
/**
* Checks whether or not a given node is a constructor.
* @param {ASTNode} node - A node to check. This node type is one of
* `Program`, `FunctionDeclaration`, `FunctionExpression`, and
* `ArrowFunctionExpression`.
* @returns {boolean} `true` if the node is a constructor.
*/
function isConstructorFunction(node) {
return (
node.type === "FunctionExpression" &&
node.parent.type === "MethodDefinition" &&
node.parent.kind === "constructor"
);
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
docs: {
description: "disallow `this`/`super` before calling `super()` in constructors",
category: "ECMAScript 6",
recommended: true,
url: "https://eslint.org/docs/rules/no-this-before-super"
},
schema: []
},
create(context) {
/*
* Information for each constructor.
* - upper: Information of the upper constructor.
* - hasExtends: A flag which shows whether the owner class has a valid
* `extends` part.
* - scope: The scope of the owner class.
* - codePath: The code path of this constructor.
*/
let funcInfo = null;
/*
* Information for each code path segment.
* Each key is the id of a code path segment.
* Each value is an object:
* - superCalled: The flag which shows `super()` called in all code paths.
* - invalidNodes: The array of invalid ThisExpression and Super nodes.
*/
let segInfoMap = Object.create(null);
/**
* Gets whether or not `super()` is called in a given code path segment.
* @param {CodePathSegment} segment - A code path segment to get.
* @returns {boolean} `true` if `super()` is called.
*/
function isCalled(segment) {
return !segment.reachable || segInfoMap[segment.id].superCalled;
}
/**
* Checks whether or not this is in a constructor.
* @returns {boolean} `true` if this is in a constructor.
*/
function isInConstructorOfDerivedClass() {
return Boolean(funcInfo && funcInfo.isConstructor && funcInfo.hasExtends);
}
/**
* Checks whether or not this is before `super()` is called.
* @returns {boolean} `true` if this is before `super()` is called.
*/
function isBeforeCallOfSuper() {
return (
isInConstructorOfDerivedClass() &&
!funcInfo.codePath.currentSegments.every(isCalled)
);
}
/**
* Sets a given node as invalid.
* @param {ASTNode} node - A node to set as invalid. This is one of
* a ThisExpression and a Super.
* @returns {void}
*/
function setInvalid(node) {
const segments = funcInfo.codePath.currentSegments;
for (let i = 0; i < segments.length; ++i) {
const segment = segments[i];
if (segment.reachable) {
segInfoMap[segment.id].invalidNodes.push(node);
}
}
}
/**
* Sets the current segment as `super` was called.
* @returns {void}
*/
function setSuperCalled() {
const segments = funcInfo.codePath.currentSegments;
for (let i = 0; i < segments.length; ++i) {
const segment = segments[i];
if (segment.reachable) {
segInfoMap[segment.id].superCalled = true;
}
}
}
return {
/**
* Adds information of a constructor into the stack.
* @param {CodePath} codePath - A code path which was started.
* @param {ASTNode} node - The current node.
* @returns {void}
*/
onCodePathStart(codePath, node) {
if (isConstructorFunction(node)) {
// Class > ClassBody > MethodDefinition > FunctionExpression
const classNode = node.parent.parent.parent;
funcInfo = {
upper: funcInfo,
isConstructor: true,
hasExtends: Boolean(
classNode.superClass &&
!astUtils.isNullOrUndefined(classNode.superClass)
),
codePath
};
} else {
funcInfo = {
upper: funcInfo,
isConstructor: false,
hasExtends: false,
codePath
};
}
},
/**
* Removes the top of stack item.
*
* And this treverses all segments of this code path then reports every
* invalid node.
*
* @param {CodePath} codePath - A code path which was ended.
* @param {ASTNode} node - The current node.
* @returns {void}
*/
onCodePathEnd(codePath) {
const isDerivedClass = funcInfo.hasExtends;
funcInfo = funcInfo.upper;
if (!isDerivedClass) {
return;
}
codePath.traverseSegments((segment, controller) => {
const info = segInfoMap[segment.id];
for (let i = 0; i < info.invalidNodes.length; ++i) {
const invalidNode = info.invalidNodes[i];
context.report({
message: "'{{kind}}' is not allowed before 'super()'.",
node: invalidNode,
data: {
kind: invalidNode.type === "Super" ? "super" : "this"
}
});
}
if (info.superCalled) {
controller.skip();
}
});
},
/**
* Initialize information of a given code path segment.
* @param {CodePathSegment} segment - A code path segment to initialize.
* @returns {void}
*/
onCodePathSegmentStart(segment) {
if (!isInConstructorOfDerivedClass()) {
return;
}
// Initialize info.
segInfoMap[segment.id] = {
superCalled: (
segment.prevSegments.length > 0 &&
segment.prevSegments.every(isCalled)
),
invalidNodes: []
};
},
/**
* Update information of the code path segment when a code path was
* looped.
* @param {CodePathSegment} fromSegment - The code path segment of the
* end of a loop.
* @param {CodePathSegment} toSegment - A code path segment of the head
* of a loop.
* @returns {void}
*/
onCodePathSegmentLoop(fromSegment, toSegment) {
if (!isInConstructorOfDerivedClass()) {
return;
}
// Update information inside of the loop.
funcInfo.codePath.traverseSegments(
{ first: toSegment, last: fromSegment },
(segment, controller) => {
const info = segInfoMap[segment.id];
if (info.superCalled) {
info.invalidNodes = [];
controller.skip();
} else if (
segment.prevSegments.length > 0 &&
segment.prevSegments.every(isCalled)
) {
info.superCalled = true;
info.invalidNodes = [];
}
}
);
},
/**
* Reports if this is before `super()`.
* @param {ASTNode} node - A target node.
* @returns {void}
*/
ThisExpression(node) {
if (isBeforeCallOfSuper()) {
setInvalid(node);
}
},
/**
* Reports if this is before `super()`.
* @param {ASTNode} node - A target node.
* @returns {void}
*/
Super(node) {
if (!astUtils.isCallee(node) && isBeforeCallOfSuper()) {
setInvalid(node);
}
},
/**
* Marks `super()` called.
* @param {ASTNode} node - A target node.
* @returns {void}
*/
"CallExpression:exit"(node) {
if (node.callee.type === "Super" && isBeforeCallOfSuper()) {
setSuperCalled();
}
},
/**
* Resets state.
* @returns {void}
*/
"Program:exit"() {
segInfoMap = Object.create(null);
}
};
}
};