fix(compiler): update memory cache for compiler using received file c…

…ontent (#3194)

The ts-jest transform is currently ignoring the file content it receives until there is already a hit in the memory cache. That prevents us from doing things like chaining transforms (see https://github.com/anc95/jest-chain-transform), as `ts-jest` will just read the original file from disk and ignore the transformation.

The changes I'm proposing were enough to resolve the issue for my use case. I haven't done extensive research into it, but it seems pretty straightforward.

src/compiler/ts-compiler.ts

@@ -386,6 +386,8 @@ export class TsCompiler implements TsCompilerInstance {
     if (!hit) {
       // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
       this._fileVersionCache!.set(fileName, 1)
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      this._fileContentCache!.set(fileName, contents)
       shouldIncrementProjectVersion = true
     } else {
       // eslint-disable-next-line @typescript-eslint/no-non-null-assertion