fixImplicitThis.ts

import {
    codeFixAll,
    createCodeFixAction,
    registerCodeFix,
} from "../_namespaces/ts.codefix.js";
import {
    ANONYMOUS,
    Debug,
    DiagnosticOrDiagnosticAndArguments,
    Diagnostics,
    emptyArray,
    factory,
    FindAllReferences,
    findChildOfKind,
    getThisContainer,
    getTokenAtPosition,
    isFunctionDeclaration,
    isFunctionExpression,
    isSourceFile,
    isThis,
    SourceFile,
    SyntaxKind,
    textChanges,
    TypeChecker,
} from "../_namespaces/ts.js";

const fixId = "fixImplicitThis";
const errorCodes = [Diagnostics.this_implicitly_has_type_any_because_it_does_not_have_a_type_annotation.code];
registerCodeFix({
    errorCodes,
    getCodeActions: function getCodeActionsToFixImplicitThis(context) {
        const { sourceFile, program, span } = context;
        let diagnostic: DiagnosticOrDiagnosticAndArguments | undefined;
        const changes = textChanges.ChangeTracker.with(context, t => {
            diagnostic = doChange(t, sourceFile, span.start, program.getTypeChecker());
        });
        return diagnostic ? [createCodeFixAction(fixId, changes, diagnostic, fixId, Diagnostics.Fix_all_implicit_this_errors)] : emptyArray;
    },
    fixIds: [fixId],
    getAllCodeActions: context =>
        codeFixAll(context, errorCodes, (changes, diag) => {
            doChange(changes, diag.file, diag.start, context.program.getTypeChecker());
        }),
});

function doChange(changes: textChanges.ChangeTracker, sourceFile: SourceFile, pos: number, checker: TypeChecker): DiagnosticOrDiagnosticAndArguments | undefined {
    const token = getTokenAtPosition(sourceFile, pos);
    if (!isThis(token)) return undefined;

    const fn = getThisContainer(token, /*includeArrowFunctions*/ false, /*includeClassComputedPropertyName*/ false);
    if (!isFunctionDeclaration(fn) && !isFunctionExpression(fn)) return undefined;

    if (!isSourceFile(getThisContainer(fn, /*includeArrowFunctions*/ false, /*includeClassComputedPropertyName*/ false))) { // 'this' is defined outside, convert to arrow function
        const fnKeyword = Debug.checkDefined(findChildOfKind(fn, SyntaxKind.FunctionKeyword, sourceFile));
        const { name } = fn;
        const body = Debug.checkDefined(fn.body); // Should be defined because the function contained a 'this' expression
        if (isFunctionExpression(fn)) {
            if (name && FindAllReferences.Core.isSymbolReferencedInFile(name, checker, sourceFile, body)) {
                // Function expression references itself. To fix we would have to extract it to a const.
                return undefined;
            }

            // `function() {}` --> `() => {}`
            changes.delete(sourceFile, fnKeyword);
            if (name) {
                changes.delete(sourceFile, name);
            }
            changes.insertText(sourceFile, body.pos, " =>");
            return [Diagnostics.Convert_function_expression_0_to_arrow_function, name ? name.text : ANONYMOUS];
        }
        else {
            // `function f() {}` => `const f = () => {}`
            // `name` should be defined because we only do this in inner contexts, and name is only undefined for `export default function() {}`.
            changes.replaceNode(sourceFile, fnKeyword, factory.createToken(SyntaxKind.ConstKeyword));
            changes.insertText(sourceFile, name!.end, " = ");
            changes.insertText(sourceFile, body.pos, " =>");
            return [Diagnostics.Convert_function_declaration_0_to_arrow_function, name!.text];
        }
    }
}