is not under 'rootDir' 'src/'. even with exclude

exclude compiler option is not working at all! I'm specifying exclude to the folder gen (and even ./gen) and still receiving the error below.

TypeScript Version: 3.3.3333

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Code

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.

Expected behavior: No errors.

Actual behavior:

error TS6059: File '.../ts-lang/gen/grammar/MyLangLexer.ts' is not under 'rootDir' 'src/'. 'rootDir' is expected to contain all source files.

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