The top-level directive include specifies which files should be included for compilation. It is based on the location of the file relative to .tsconfig.json and by default includes all files in the project within the ** wildcard. Files not specified in the include directive will not be compiled.
The compilerOptions.rootDir setting determines the root directory for the output at outDir. By default, it identifies the common path among the included folders. For instance, in a project with files src/services/user.ts and src/services/auth.ts, the rootDir would automatically adjust to src/services/ (i.e., the longest common path shared by all input files). Consequently, the output directory structure would appear as follows:
dist
├── auth.js
└── user.js
If manually specifying rootDir as src, the resulting output directory structure would be:
dist
└── services
├── auth.js
└── user.js
Furthermore, if there are files outside of the designated rootDir that are included in the include directive, an error will occur:
error TS6059: File '~/project/outside.ts' is not under 'rootDir' '~/project/src'. 'rootDir' must encompass all source files.
The file is part of the program due to:
Inclusion pattern '**/*' matches it in '~/project/tsconfig.json'