Cgo packages cannot have a package name different than its folder name

Go allows a package name different from its folder name. However, we have to tell cgo the package name so it generates .go files with right package declaration. It was possible to do that at revision fdb121f6f803ad14c7ab77c0381e81da6ae06fab, but after #1994, it is no longer possible. As a result, we cannot build github.com/mattn/go-sqlite3 with Buck anymore.

Steps to reproduce the error:

1. Checkout the sqlite branch of my fork of buck
2. Run this test

As a comparison, Go toolchain is able to build the same package:

cd test/com/facebook/buck/features/go/testdata/cgo
GOPATH=$(pwd) go run src/different_package/cli/main.go

In order for the Go toolchain to build the package, we cannot change the import statements in main.go.

[mkaczanowski]

After long discussion with @linzhp on slack we got to the root of the problem, which is frankly speaking very non-obvious.

Because cgo package is always embedded in go binary generated by “go build” the package name is not expected to be the same as the binary package name.

“go build” would infer the package name from the source files (not the location / directory name) and use it as “cgo” package_name.

For example:

go_library(
    name='lib',
    package_name="github.com/mattn/go-sqlite3",
    srcs=['doc.go', 'sqlite3_func_crypt.go', 'sqlite3_go18.go'],
    cgo=':cgo_lib',
    visibility=['PUBLIC']
)

cgo_library(
    name='cgo_lib',
    package_name = "sqlite3",

This used to work before, because the package_name is different for cgo and go libraries. The former is not the import path (ex. github.com/whatever/go-sqlite3) but sqlite3 which “go build” would infer from the source files.

The solution is to add extra argument such as:

declared_package_name = "sqlite3"

to cgo_library

[mkaczanowski]

It’s used in only one place (CGoGenImport.java) so likely it can