This PR fixes a critical performance issue where the language
service makes a MASSIVE number of filesystem calls when performing
module resolution.
This is because there is no caching. To make matters worse, module
resolution is performed for **every** program change (which means every
few keystrokes trigger a massive number of fs calls).
PR Close#32479
The language service relies on a "context" file that is used as the
canonical "containing file" when performing module resolution.
This file is unnecessary since the language service host's current
directory always default to the location of tsconfig.json for the
project, which would give the correct result.
This refactoring allows us to simplify the "typescript host" and also
removes the need for custom logic to find tsconfig.json.
PR Close#32015
With this change we reduce the amount of IO operations. This is especially a huge factor in windows since IO ops are slower.
With this change mainly we cache `existsSync` and `readFileSync` calls
Here's the results
Before
```
//packages/language-service/test:test
INFO: Elapsed time: 258.755s, Critical Path: 253.91s
```
After
```
//packages/language-service/test:test
INFO: Elapsed time: 66.403s, Critical Path: 63.13s
```
PR Close#30585
The 2.6 version of TypeScript's `resolveModuleName` started to
require paths passed to be separated by '/' instead of being
able to handle '\'.
`ngc` and `ng` already do this transformation.
Fixes: #21811
PR Close#21812
Keen Yee Liau
Keen Yee Liau
Alan
Chuck Jazdzewski