fix(compiler): make sure language service use updated compiler options

[cexbrayat]

Summary

When a file initially exists in compiler file set when TsCompiler is created, later in getCompiledOutput the value of compilerOptions which makes LanguageService is not aware of because _updateMemoryCache checks and sees that the file is the same so projectVersion value is not increased which makes LanguageService uses the outdated _compilerOptions.

This commit adds a comparison via JSON stringify between _compilerOptions and _initialCompilerOptions. If there is a difference, increase projectVersion for LanguageService.

This regression came to light when bumping vue-jest to ts-jest v27.
The tsconfig used has : "module": "es2015", and ts-jest used to compile the files to commonjs anyway.
This is no longer the case when using ts-jest v27.0.0

Closes #2629

Test plan

Added unit test
Green CI

Does this PR introduce a breaking change?

• Yes
• No

Other information

N.A.

[ahnpnl]

projectVersion is bumped when memory cache is updated, not before. Would you please link the issue which is caused by v27?

Would be good to have a reproduce scenario first to see what causes the problem. Bumping projectVersion can cause the whole language service mechanism kicks in, including module resolution, file reading, etc.. in LanguageServiceHost.

[ahnpnl]

ok the scenario happens when a file already exists in initial compiler file set and initially, module is es2015. Later when LanguageService starts compilation, updateMemoryCache checks and sees that file already exists while compilerOptions is already updated with module: commonjs. LanguageService will then use that module: es2015 to compile which leads to the problem.

The solution I'd say is: at this line https://github.com/kulshekhar/ts-jest/blob/master/src/compiler/ts-compiler.ts#L408 do a check to see if this._compilerOptions vs this._initialCompilerOptions is different. If it is different, simply set shouldIncrementProjectVersion to true.

[coveralls]

Pull Request Test Coverage Report for Build 880000634

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 94.394%

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Totals
Change from base Build 878331062:	0.02%
Covered Lines:	1011
Relevant Lines:	1037

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💛 - Coveralls

[cexbrayat]

@ahnpnl thank you for your quick response and release (and much better fix 👍).