Performance of getSemanticDiagnostics in compiler API

The setup is somewhat similar to the one in the compiler API example (https://github.com/Microsoft/TypeScript/wiki/Using-the-Compiler-API#incremental-build-support-using-the-language-services)

The problem, as in the example, is that errors are reported only for files that were directly changed. It doesn't cover the case in which the changed file was a dependency of another file, and even though the file depending on it was not changed, it will still have errors, which won't be reported.

To be more specific, the setup I am talking about is ts-loader + webpack.

What happens is that getSemanticDiagnostics(file) has to be called for every file in the project, which ends up increasing the incremental build times considerably. Even program.getSemanticDiagnostics() iterates through all of the source files as it is seen in the typescript source code.

I can only see this problem fixed from the compiler API. It could expose a method which finds all files dependent on a given file. Because in an incremental build only a single file changed, this should be faster than calling getSemanticDiagnostics() for each and every project file.

The alternative would be some sort of caching on getSemanticDiagnostics() itself, but the compiler would probably have to do internally the same work as above to invalidate the cache on file change. This seems to be equivalent to a getSemanticDiagnosticsForFileAndDependents(file)-like function.

首先阅读 TypeScript compiler API 中 getSemanticDiagnostics(file) 和 program.getSemanticDiagnostics() 的实现，包括 issue 中引用的源代码。确定增量构建如何识别依赖于已更改文件的文件，然后评估一种 API 或缓存方案，避免检查项目中的每个文件，同时仍报告所有受影响的诊断信息。