[rcoreilly]

A package variable whose initializer uses a declaration of another file of its package, such as a struct type, is initialized lazily through a getter, since that file may not be evaluated yet. But a variable that only reads such a variable stayed eager, so its initializer called the getter at module evaluation, which ran the lazy initializer early anyway. When the file declaring the class is evaluated after the reader's file, as happens in an import cycle between the files, this throws a ReferenceError (Cannot access 'X' before initialization).

github.com/pkg/sftp has this pattern: sftp.go declares supportedSFTPExtensions as a slice of sshExtensionPair, a type of packet.go, and then sftpExtensions = supportedSFTPExtensions. A program that imports it failed at load time.

lazyPackageVars now makes such readers lazy too, transitively, through markLazyReaders. It only propagates from variables made lazy because their initializers or zero values need other files, so the whole-program handling of deferred tables is unchanged, and it leaves eager the initializers with runtime effects and blank variables, which must still run at package initialization.

The cross_file_struct_typeinfo_zero fixture gains a third file, whose table of a type of b.go is read by another variable, and b.go uses that variable, so b.go is evaluated after it; it failed with the ReferenceError before. The full compiler test suite passes, with no other generated fixture changes.