addMissingConst.ts

import {
    codeFixAll,
    createCodeFixAction,
    registerCodeFix,
} from "../_namespaces/ts.codefix.js";
import {
    Diagnostics,
    every,
    Expression,
    findAncestor,
    getTokenAtPosition,
    isArrayLiteralExpression,
    isAssignmentExpression,
    isBinaryExpression,
    isExpressionStatement,
    isForInOrOfStatement,
    isIdentifier,
    Node,
    Program,
    SourceFile,
    SyntaxKind,
    textChanges,
    tryAddToSet,
    TypeChecker,
} from "../_namespaces/ts.js";

const fixId = "addMissingConst";
const errorCodes = [
    Diagnostics.Cannot_find_name_0.code,
    Diagnostics.No_value_exists_in_scope_for_the_shorthand_property_0_Either_declare_one_or_provide_an_initializer.code,
];

registerCodeFix({
    errorCodes,
    getCodeActions: function getCodeActionsToAddMissingConst(context) {
        const changes = textChanges.ChangeTracker.with(context, t => makeChange(t, context.sourceFile, context.span.start, context.program));
        if (changes.length > 0) {
            return [createCodeFixAction(fixId, changes, Diagnostics.Add_const_to_unresolved_variable, fixId, Diagnostics.Add_const_to_all_unresolved_variables)];
        }
    },
    fixIds: [fixId],
    getAllCodeActions: context => {
        const fixedNodes = new Set<Node>();
        return codeFixAll(context, errorCodes, (changes, diag) => makeChange(changes, diag.file, diag.start, context.program, fixedNodes));
    },
});

function makeChange(changeTracker: textChanges.ChangeTracker, sourceFile: SourceFile, pos: number, program: Program, fixedNodes?: Set<Node>) {
    const token = getTokenAtPosition(sourceFile, pos);
    const forInitializer = findAncestor(token, node =>
        isForInOrOfStatement(node.parent) ? node.parent.initializer === node :
            isPossiblyPartOfDestructuring(node) ? false : "quit");
    if (forInitializer) return applyChange(changeTracker, forInitializer, sourceFile, fixedNodes);

    const parent = token.parent;
    if (isBinaryExpression(parent) && parent.operatorToken.kind === SyntaxKind.EqualsToken && isExpressionStatement(parent.parent)) {
        return applyChange(changeTracker, token, sourceFile, fixedNodes);
    }

    if (isArrayLiteralExpression(parent)) {
        const checker = program.getTypeChecker();
        if (!every(parent.elements, element => arrayElementCouldBeVariableDeclaration(element, checker))) {
            return;
        }

        return applyChange(changeTracker, parent, sourceFile, fixedNodes);
    }

    const commaExpression = findAncestor(token, node =>
        isExpressionStatement(node.parent) ? true :
            isPossiblyPartOfCommaSeperatedInitializer(node) ? false : "quit");
    if (commaExpression) {
        const checker = program.getTypeChecker();
        if (!expressionCouldBeVariableDeclaration(commaExpression, checker)) {
            return;
        }

        return applyChange(changeTracker, commaExpression, sourceFile, fixedNodes);
    }
}

function applyChange(changeTracker: textChanges.ChangeTracker, initializer: Node, sourceFile: SourceFile, fixedNodes?: Set<Node>) {
    if (!fixedNodes || tryAddToSet(fixedNodes, initializer)) {
        changeTracker.insertModifierBefore(sourceFile, SyntaxKind.ConstKeyword, initializer);
    }
}

function isPossiblyPartOfDestructuring(node: Node): boolean {
    switch (node.kind) {
        case SyntaxKind.Identifier:
        case SyntaxKind.ArrayLiteralExpression:
        case SyntaxKind.ObjectLiteralExpression:
        case SyntaxKind.PropertyAssignment:
        case SyntaxKind.ShorthandPropertyAssignment:
            return true;
        default:
            return false;
    }
}

function arrayElementCouldBeVariableDeclaration(expression: Expression, checker: TypeChecker): boolean {
    const identifier = isIdentifier(expression) ? expression :
        isAssignmentExpression(expression, /*excludeCompoundAssignment*/ true) && isIdentifier(expression.left) ? expression.left :
        undefined;
    return !!identifier && !checker.getSymbolAtLocation(identifier);
}

function isPossiblyPartOfCommaSeperatedInitializer(node: Node): boolean {
    switch (node.kind) {
        case SyntaxKind.Identifier:
        case SyntaxKind.BinaryExpression:
        case SyntaxKind.CommaToken:
            return true;
        default:
            return false;
    }
}

function expressionCouldBeVariableDeclaration(expression: Node, checker: TypeChecker): boolean {
    if (!isBinaryExpression(expression)) {
        return false;
    }

    if (expression.operatorToken.kind === SyntaxKind.CommaToken) {
        return every([expression.left, expression.right], expression => expressionCouldBeVariableDeclaration(expression, checker));
    }

    return expression.operatorToken.kind === SyntaxKind.EqualsToken
        && isIdentifier(expression.left)
        && !checker.getSymbolAtLocation(expression.left);
}