chore(compiler): clean up codes and update docs for isolatedModules: false

docs/user/config/index.md

@@ -190,7 +190,6 @@ All options have default values which should fit most of the projects. Click on
 | [**`compiler`**][compiler] | [TypeScript module to use as compiler.][compiler] | `string` | `"typescript"` |
 | [**`tsConfig`**][tsConfig] | [TypeScript compiler related configuration.][tsConfig] | `string`\|`object`\|`boolean` | _auto_ |
 | [**`isolatedModules`**][isolatedModules] | [Disable type-checking][isolatedModules] | `boolean` | `false` |
-| [**`compilerHost`**][compilerHost] | [Use TypeScript Compiler API][compilerHost] | `boolean` | `false` |
 | [**`diagnostics`**][diagnostics] | [Diagnostics related configuration.][diagnostics] | `boolean`\|`object` | `true` |
 | [**`babelConfig`**][babelConfig] | [Babel(Jest) related configuration.][babelConfig] | `boolean`\|`object` | _disabled_ |
 | [**`stringifyContentPathRegex`**][stringifyContentPathRegex] | [Files which will become modules returning self content.][stringifyContentPathRegex] | `string`\|`RegExp` | _disabled_ |

docs/user/config/isolatedModules.md

@@ -10,6 +10,21 @@ You'll lose type-checking ability and some features such as `const enum`, but in
 
 Here is how to disable type-checking and compile each file as an isolated module:
 
+## Performance
+
+Using `isolatedModules: false` (default) might impact the performance of your tests. To solve this, there are 2 ways:
+- Either use `isolatedModules: true` (see disadvantages above)
+- Or use `isolatedModules: false` and check your `tsconfig.json` which `ts-jest` uses. Make sure that your test `tsconfig` only includes the files which are needed
+for your test environment. These necessary files can **ONLY** be:
+    - Your global modules imported via namespaces
+    - Polyfills
+    - Other test environment files
+
+When creating `LanguageService` instance, `LanguageServiceHost` takes all the files declared by the combination of `files`, 
+`includes` and `excludes` which are provided via your test `tsconfig`. If `tsconfig` includes all the files in a project, 
+this will make internal `TypeScript` take lots of time because `TypeScript` is busy with reading files which creates 
+lots of unnecessary I/O threads before it actually creates the instance which will impact to the performance.
+
 ### Example
 
 <div class="row"><div class="col-md-6" markdown="block">

e2e/__helpers__/templates.ts

@@ -7,4 +7,3 @@ export enum PackageSets {
 }
 export const allValidPackageSets = [PackageSets.default, PackageSets.babel7, PackageSets.babel7StringConfig]
 export const allPackageSetsWithPreset = [PackageSets.default, PackageSets.babel7, PackageSets.babel7StringConfig]
-export const allPackageSetsWithProgram = [PackageSets.default, PackageSets.babel7, PackageSets.babel7StringConfig]