[emcfarlane]

When an option import publicly imports a file that another import also brings in, the experimental compiler cleared the option import's flag. The file was then written to dependency instead of option_dependency, and it lost its options-only restriction. For example:

// a.proto
import "other.proto";      // other.proto has `import option "b.proto"`
import option "b.proto";   // b.proto has `import public "c.proto"`

protoc emits option_dependency: ["b.proto"]. We emitted dependency: ["other.proto", "b.proto"]. Edition 2026 makes this common, because google/protobuf/json_options.proto publicly imports json_enumvalue_options.proto.

The cause was not enough details in the flags to handle this case. Both to record how the dependency was imported and whether it is restricted to options. New field dependency is true when a file is reachable through a non-option import. Which is either directly, or through that import's public export. Visibility checks now use dependency.