typescript-poor-man-reflection

An unconventional way of getting TypeScript code information (like types), as text.

NOT READY, not yet...

Why ?

• https://github.com/Microsoft/TypeScript/issues/14419
• I need to get a type text at runtime and I cannot hardcode it as string since it will get outdated on code refactors
• I don't want to use a tsc wrapper like ttypescript
• And then I discovered a lots of other things can be accomplished by running code at compile time...

What ?

A preprocessor tool to modify input TypeScript files embedding requested types or nodes text in the code. Supports several extractor implementations. See Default Extractors.

The tool will modify TypeScript source files calling the library's functions, embedding referenced node's text in the source file. It should be called before tsc or before npm test, and it can be called with the option --clean to clean-up source files (for example before commit or after npm test).

Cost: You need to pre-process your TS files before compiling them with tsc in order for this to work and they will be modified.

You can undo the changes later, perhaps before commit / linting the code. Or perhaps never, if you maintain your instrumented files isolated probably you won't notice any changes and the default transformation is very discrete.

Usage

npm install -D typescript-poor-man-reflection
# preprocess before compile
npx typescript-poor-man-reflection
npx tsc
npm test
# Undo the changes before lint / commit
npx typescript-poor-man-reflection --clean
nxp prettier

Snippets

Compile-time conditionals

const logger = If({
  condition: () => process.env.NODE_ENV==='production',
  then: () => new LightLogger(),
  else: () => new DevLogger()
})

Overrides

Want to make sure your classes methods and properties are actually overriding a super class/interface member ?

import { Overrides } from 'typescript-poor-man-reflection'
import { AbstractAnimal, Alive } from 'a-library'
export class ConcreteAnimal extends AbstractAnimal implements Alive {
  energy: number = Overrides(1)
  eat(food: Alive) {
    Override()
    this.energy++
  }
}

If property energy or method eat are not overriding a super class property or method respectively, then the extractor will generate a call with a Type Error so you are aware if they are actually overriding something, at compile time.

ReadFiles

Embed files in your source, at compile time:

// assets.ts - contains example files embedded from FS at compile time
// files exports an array of objects `{name: string, content: string}`
import { ReadFiles } from 'typescript-poor-man-reflection'
export const files = ReadFiles({path: '../examples/example*.ts'})

Organize imports - remove unused - infer types, exec

Execute TypeScript known refactors in current or all files:

import { OrganizeImports, RemoveUnused, Exec } from 'typescript-poor-man-reflection'
OrganizeImports({path: 'src/**/*.ts*'})
RemoveUnused({path: 'src/**/*.ts*'})
if(Exec('npm run prettier').code!==0){
  process.exit(1)
}
// or just in current file:
InferTypes()

Refactor tools

(Expect more!)

TODO: extract interface

TypeText

Be able to get types text so we don't hardcode them as strings. Taken from tsd-check-runtime - its sibling project - using jest matchers.

import { Type } from 'tsd-check-runtime';
import {UnionOf} from '../util'
interface A {}
describe('toMatchType', () => {
  var testVariable1: B = { b: 8 }
  it('using toMatchType against types, nodes and strings', () => {
    // hardcoded strings (no reflection - Bad will get outdated on refactor)
    expect('a').not.toMatchType(`UnionOf<[1, false]>`)
    // reflection - referencing nodes from several scopes
    expect(1).toMatchType(Type<UnionOf<[1, false]>>())
    interface B extends A { b: number }
    expect(testVariable1).toMatchType(Type<B>, { exactly: true })
    expect(testVariable1).toMatchType('B')
    interface II {
      foo: Date[][]
      m(): string[]
    }
    const var2 = number[]
    expect((II, mReturnType) =>
      `var a: ${II} = {foo: [], m() { return null as any as ${mReturnType} } }`
    ).not.toCompile(Type<II>(), Type<typeof var2>())
  })
})

As you can see I'm referencing types as text, declared in any scope. A call like Type<typeof var2>(), in this case, will return the string "Type<UnionOf<[1, false]>>()". That's tsd-check-runtime project's implementation specialized for testing, builded un top of this framework which is easy to extend.

Usage

npm install -D typescript-poor-man-reflection 

We will use one of the built-in tools, TypeText that extracts given type text as a string.

import { TypeText } from 'typescript-poor-man-reflection'
type UnionOf<T extends any[]> = T[number]
const x = TypeText<UnionOf<[1, Date[]]>>()
const z = TypeText<UnionOf<[1, boolean | string]>>()
console.log(x, z)

Executing the program, gives, as expected:

$ npx ts-node test.ts 
undefined undefined

But now we transpile our code and:

$ npx typescript-poor-man-reflection
$ npx ts-node test.ts 
UnionOf<[1, Date[]]> UnionOf<[1, boolean | string]>

But at a terrible cost, your files have been modified!

Data Modes

(Different modalities on how your files are modified)

• folderFile (Default). The data is stored in a separate file that exports a function to access to array. An import declaration will be added to the file and function calls will use the imported function to access the array. There will be one of these files per folder with the name given by option extractorDataFolderFileName that will contain the data of all this folder's immediate children.

• If prependVariable, an array variable will be prepended at the top of the same file and function calls will access the array directly.

• If asArgument then the whole thing will be passed as a single string in the parameter (this is mostly useful for debugging since it will pollute the code a lot)

Options

In general all API options are supported in the CLI as long as their types supported (function options are not supported in the CLI). All options are documented in ReplaceProjectFunctionCallOptions interface.

CLI API

npx typescript-poor-man-reflection

Options:

• --clean clean up arguments from project previously modified with this tool

• --tsConfigFilePath get project configuration from different file than default './tsconfig.json'

• --extractorDataMode data extraction mode: 'folderFile': (default) all folder's files data is stored in a single new file (--extractorDataFolderFileName). 'prependVariable' each file data is stored in a variable which is declared at the top of the file (--extractorDataVariableName)

• --filePattern if provided it will only modify files that match the given glob. Example: --filePattern "/tests//withTypes/**/.ts"

• --moduleSpecifier extract only from function calls imported from this module

• --extractorDataVariableName name of the variable for --extractorDataMode==='prependVariable'

• --extractorDataFolderFileName name of the file for --extractorDataMode==='folderFile'

• --out write modified files in that folder instead of writing files in-place

• --debug print debug information while executing

Workflow

Basically use this only for test projects. Run npx typescript-poor-man-reflection before npm test or tsc, ts-node, jest, etc.

To rollback the changes execute the following command. It will clean all the added arguments:

npx typescript-poor-man-reflection --clean

API

• Per-project JS API
• Per-file JS API
• CLI main function

All the options apply to the CLI if their type supports it (not functions)

Motivation

Trying to test types utilities, like:

import TypeText from 'typescript-poor-man-reflection'
import { UnionOf } from '..'
test('UnionOf transform a tuple into an union type', () => {
  expect(2).not.toMatchType(TypeText<UnionOf<[1, false]>>)
  expect(1).toMatchType(TypeText<UnionOf<[1, false]>>)
})

Trying to develop a preprocessing tool to mutate TypeScript and replace certain function call expressions with referenced type text so we have access to this info at runtime. tsd-check is not enough for me since I need to verify types at runtime to reproduce false positives, and isNot helpers. (I cannot reproduce an error at compile time in a test)

TODO and ideas

See (TODO.md)[TODO.md]