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…JS (#44271)

* Always issue cannot find name did-you-mean error

This PR issues "cannot find ${name}, did you mean ${name}" errors for
identifiers and propery access expressions in JS files *without*
`// @ts-check` and without `// @ts-nocheck`. This brings some benefits of
Typescript's binder to all Javascript users, even those who haven't
opted into Typescript checking.

```js
export var inModule = 1
inmodule.toFixed() // errors on exports

function f() {
    var locals = 2
    locale.toFixed() // errors on locals
}
var object = {
    spaaace: 3
}
object.spaaaace // error on read
object.spaace = 2 // error on write
object.fresh = 12 // OK, no spelling correction to offer
```

To disable the errors, add `// @ts-nocheck` to the file. To get the
normal checkJs experience, add `// @ts-check`.

== Why This Works ==

In a word: precision. This change has low recall — it misses lots
of correct errors that would be nice to show — but it has high
precision: almost all the errors it shows are correct. And they come
with a suggested correction.

Here are the ingredients:

1. For unchecked JS files, the compiler suppresses all errors except
two did-you-mean name resolution errors.
2. Did-you-mean spelling correction is already tuned for high
precision/low recall, and doesn't show many bogus errors even in JS.
3. For identifiers, the error is suppressed for suggestions from global files.
These are often DOM feature detection, for example.
4. For property accesses, the error is suppressed for suggestions from
other files, for the same reason.
5. For property accesses, the error is suppressed for `this` property
accesses because the compiler doesn't understand JS constructor
functions well enough.
In particular, it doesn't understand any inheritance patterns.

== Work Remaining ==

1. Code cleanup.
2. Fix a couple of failures in existing tests.
3. Suppress errors on property access suggestions from large objects.
4. Combine (3) and (4) above to suppress errors on suggestions from other, global files.
5. A little more testing on random files to make sure that precision
is good there too.
6. Have people from the regular Code editor meeting test the code and
suggest ideas.

* all (most?) tests pass

* NOW they all pass

* add tonnes of semi-colons

* restore this.x check+add a test case

* make ts-ignore/no-check codefix work in unchecked js

* Issues errors only in the language service

* add a few more tests

* fix incorrect parentheses

* More cleanup in program.ts

* Improve readability of isExcludedJSError

* make diff in program.ts smaller via closure

* Switch unchecked JS did-you-mean to suggestion

Instead of selectively letting errors through.

* undo more missed changes

* disallow ignoring suggestions

* Issue different messages for plain JS than others

Straw text for the messages, I just changed the modals to avoid name
collisions.
e53f19f

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TypeScript

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TypeScript is a language for application-scale JavaScript. TypeScript adds optional types to JavaScript that support tools for large-scale JavaScript applications for any browser, for any host, on any OS. TypeScript compiles to readable, standards-based JavaScript. Try it out at the playground, and stay up to date via our blog and Twitter account.

Find others who are using TypeScript at our community page.

Installing

For the latest stable version:

npm install -g typescript

For our nightly builds:

npm install -g typescript@next

Contribute

There are many ways to contribute to TypeScript.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.

Documentation

Building

In order to build the TypeScript compiler, ensure that you have Git and Node.js installed.

Clone a copy of the repo:

git clone https://github.com/microsoft/TypeScript.git

Change to the TypeScript directory:

cd TypeScript

Install Gulp tools and dev dependencies:

npm install -g gulp
npm ci

Use one of the following to build and test:

gulp local             # Build the compiler into built/local.
gulp clean             # Delete the built compiler.
gulp LKG               # Replace the last known good with the built one.
                       # Bootstrapping step to be executed when the built compiler reaches a stable state.
gulp tests             # Build the test infrastructure using the built compiler.
gulp runtests          # Run tests using the built compiler and test infrastructure.
                       # You can override the specific suite runner used or specify a test for this command.
                       # Use --tests=<testPath> for a specific test and/or --runner=<runnerName> for a specific suite.
                       # Valid runners include conformance, compiler, fourslash, project, user, and docker
                       # The user and docker runners are extended test suite runners - the user runner
                       # works on disk in the tests/cases/user directory, while the docker runner works in containers.
                       # You'll need to have the docker executable in your system path for the docker runner to work.
gulp runtests-parallel # Like runtests, but split across multiple threads. Uses a number of threads equal to the system
                       # core count by default. Use --workers=<number> to adjust this.
gulp baseline-accept   # This replaces the baseline test results with the results obtained from gulp runtests.
gulp lint              # Runs eslint on the TypeScript source.
gulp help              # List the above commands.

Usage

node built/local/tsc.js hello.ts

Roadmap

For details on our planned features and future direction please refer to our roadmap.