E091: A module exists in this build, but this package may not import it

// turf.toml of myapp:  [dependencies] plotter = { path = "../plotter" }// plotter depends on geometryimport geometry;// ERROR: Package 'geometry' is not a dependency of 'myapp'.//     It is in this build because 'plotter' depends on it.//   Hint: A package can import only its own modules, its direct//   dependencies and the standard library. Add 'geometry' to//   [dependencies] in myapp's turf.toml to import it here.

In a project, import m; can name exactly three kinds of module:

• one of your own package’s modules (a m.tr anywhere under src/),
• a package you list under [dependencies], by its package name, or
• a standard-library module.

This error means m is in the build but is none of those three for the package doing the import. It comes in two forms.

A transitive dependency. The package is built because something you depend on depends on it, but you do not depend on it yourself. Using it anyway would make your code break the day that dependency stops needing it, so add it to your own [dependencies].

Another package’s internal module. Every module of a package except its root module (src/<package name>.tr) is internal to it:

import shapes;// ERROR: Module 'shapes' is internal to package 'geometry'.

Import the package itself (import geometry;) and use what its root module makes pub. If the package’s author meant shapes to be part of its interface, the root module is where they expose it.

This is a different error from “Could not find module” (E027): here the file exists, and a rule decides it is out of reach.

Run turf --explain E091 in a terminal to read this again.