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Crazy checker.ts refactor experiment (25kloc)

See original GitHub issue

I have made tool-assisted refactoring experiment on typeChecker. The goal is to convert checker.ts from incapsulated js scope to a class. For better extensibility and publicity (#17680).

All tests are passing, excluding linting (because of auto converting). We can fix linting issues later.

How I refactored 25k lines of code:

  1. All types moved to ts namespace out of createTypeChecker;
  2. Class TypeCheckerImpl was created.
  3. All variables from createTypeChecker moved to public properties of TypeCheckerImpl;
  4. Property initializers were moved to constructor. (because of constructor parameters dependency) declarations now looks ugly, because
    public propName = (false as true) && this.someMethod();
    is only way to auto infer type of function return value; We can fix it later.
  5. All nested functions from createTypeChecker converted to public methods of TypeCheckerImpl;
  6. For all converted functions auto inserted “this” keyword.
  7. For methods that contain nested functions I have to create ugly conv_self to enclosure “this”.
  8. Added ugly code to bind all methods. We can fix it later.
  9. Now TypeCheckerImpl instance is not exposed to public, but I want to do it later.

Here is commit in my fork: Unfortunetly GitHub can`t show diff, and that is one more point for necessity of refactoring.

Raw checker.ts before


This is only experiment.

I have spend around 16 hours for these transforms. I think that this experiment is successful. For better typescript future I think checker.ts should be separated into multiple files/classes, and this is the first step. This code is not merge ready. Of course we should think about methods to be provided to public api, and may be unsafe access for people who do really complicated transformations.

What do you think about it?

I can dedicate more time, improve documents and publish tools I’ve made, if more people support this experiment.

Issue Analytics

  • State:open
  • Created 6 years ago
  • Reactions:18
  • Comments:13 (10 by maintainers)

github_iconTop GitHub Comments

andy-mscommented, Aug 22, 2017

I ran our internal performance tests and it looks like there is a large increase in check time. (There were also large increases in emit time, which may just be my hard drive acting up.) There was no change to parse or bind time or memory usage.

Monaco - node (v8.2.1, x64)

Project Baseline Current Delta Best Worst
Memory used 357,006k (± 0.00%) 356,252k (± 0.00%) -754k (- 0.21%) 356,247k 356,258k
Parse Time 2.10s (± 1.10%) 2.10s (± 0.62%) +0.01s (+ 0.43%) 2.09s 2.12s
Bind Time 0.81s (± 1.15%) 0.81s (± 1.61%) +0.01s (+ 0.74%) 0.80s 0.83s
Check Time 4.19s (± 0.60%) 4.89s (± 0.53%) +0.70s (+ 16.62%) 4.86s 4.92s
Emit Time 2.77s (± 0.73%) 6.92s (± 1.01%) +4.15s (+149.96%) 6.88s 7.03s
Total Time 9.87s (± 0.45%) 14.74s (± 0.48%) +4.87s (+ 49.37%) 14.69s 14.84s

Monaco - tsc (x86)

Project Baseline Current Delta Best Worst
Parse Time 1.51s (± 3.64%) 1.48s (± 0.88%) -0.03s (- 1.85%) 1.47s 1.50s
Bind Time 0.58s (± 1.82%) 0.58s (± 2.95%) -0.01s (- 1.03%) 0.56s 0.60s
Check Time 3.98s (± 0.98%) 4.93s (± 0.58%) +0.96s (+ 24.13%) 4.89s 4.95s
Emit Time 7.54s (± 6.52%) 7.24s (± 0.41%) -0.30s (- 3.98%) 7.23s 7.29s
Total Time 13.61s (± 3.93%) 14.24s (± 0.43%) +0.63s (+ 4.64%) 14.16s 14.31s

TFS - node (v8.2.1, x64)

Project Baseline Current Delta Best Worst
Memory used 309,696k (± 0.01%) 308,820k (± 0.01%) -876k (- 0.28%) 308,805k 308,841k
Parse Time 1.53s (± 1.92%) 1.54s (± 4.00%) +0.01s (+ 0.85%) 1.45s 1.58s
Bind Time 0.68s (± 4.95%) 0.69s (± 10.07%) +0.01s (+ 1.02%) 0.66s 0.80s
Check Time 3.60s (± 0.51%) 4.24s (± 0.79%) +0.64s (+ 17.84%) 4.20s 4.28s
Emit Time 2.45s (± 0.33%) 4.09s (± 1.23%) +1.65s (+ 67.31%) 4.06s 4.17s
Total Time 8.26s (± 0.33%) 10.57s (± 0.66%) +2.31s (+ 27.92%) 10.51s 10.66s

TFS - tsc (x86)

Project Baseline Current Delta Best Worst
Parse Time 1.09s (± 5.00%) 1.07s (± 0.90%) -0.02s (- 1.84%) 1.06s 1.08s
Bind Time 0.58s (± 5.24%) 0.57s (± 3.35%) -0.00s (- 0.86%) 0.55s 0.59s
Check Time 3.26s (± 1.15%) 3.95s (± 1.10%) +0.70s (+ 21.44%) 3.90s 3.99s
Emit Time 4.44s (± 1.49%) 4.36s (± 1.21%) -0.08s (- 1.85%) 4.29s 4.41s
Total Time 9.37s (± 1.10%) 9.96s (± 0.86%) +0.59s (+ 6.32%) 9.89s 10.05s

I’d really like to see the checker cut down to size – it’s so big that vscode doesn’t support collapsing code, and it takes several seconds to update errors. I think some of the candidates for removal from checker.ts were isTypeAssignableTo and typeToString. @sandersn might have some comments.

RyanCavanaughcommented, Jan 26, 2021

This gets asked a ton of times, so here’s the short version

Imagine you have this code structure

function fn(x) {
  // There are ~450 of these variables
  let y1 = someFunc1(x);
  let y2 = someFunc2(x);

  // There are ~1200 of these functions
  function a() {
    console.log(y1 - x);
  function b(z) {
    console.log(y2 + x * z);

It is a fact in modern JS engines that bare-name lookups like y1 and y2 are much faster than property accesses like obj.y1 and obj.y2. The challenge, then: how do you “split up” fn in a way that preserves that performance improvement?

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