Attachment: Download

Issue Description:

I have a project that's structured as follows:

{{ - Sources}}
{{ |- Clibuv}}
{{ |- Foo}}

where Clibuv is a wrapper around the libuv library (in real life it's a git submodule under Sources/Clibuv/), and Foo depends on Clibuv. See attached Foo-51.zip.

The project builds fine in Swift 5.1.

With Swift 5.2.3 however, I get errors like these:

While building module 'Clibuv' imported from Foo/Sources/Foo/main.c:2:

In file included from <module-includes>:3:

Foo/Sources/Clibuv/libuv/include/uv/bsd.h:25:9: warning: 'UV_PLATFORM_FS_EVENT_FIELDS' macro redefined [-Wmacro-redefined]

{{#define UV_PLATFORM_FS_EVENT_FIELDS }}

{{ ^}}

Foo/Sources/Clibuv/libuv/include/uv/darwin.h:45:9: note: previous definition is here

#define UV_PLATFORM_FS_EVENT_FIELDS

Checking the build output I see that a module map is automatically generated for Clibuv:

module Clibuv {

{{ umbrella "/Users/ylee/Downloads/Foo/Sources/Clibuv/libuv/include"}}

{{ export *}}

{{}}}

To address the build issue, I add a custom module map under Sources/Clibuv/include/:

module Clibuv {

{{ header "uv.h"}}

{{ export *}}

{{}}}

And updated Package.swift. See Foo-52-fix.zip.

{{ }}