error: `Foo` declared multiple times
  --> a1.proto:4:9
   |
 4 | message Foo {
   |         ^^^ first here, as a message type
   |
  ::: a2.proto:4:9
   |
 4 | message Foo {
   |         --- ...also declared here
   |
   = help: symbol names must be unique across all files; for example, "a2.proto"
           declares `pkgname.Foo` but it is not directly imported

error: `Zed` declared multiple times
  --> a1.proto:11:9
   |
11 | message Zed {}
   |         ^^^ first here, as a message type
   |
  ::: a2.proto:11:9
   |
11 | message Zed {}
   |         --- ...also declared here
   |
   = help: symbol names must be unique across all files; for example, "a2.proto"
           declares `pkgname.Zed` but it is not directly imported

error: `Svc` declared multiple times
  --> a1.proto:12:9
   |
12 | service Svc {}
   |         ^^^ first here, as a service definition
   |
  ::: a2.proto:12:9
   |
12 | service Svc {}
   |         --- ...also declared here
   |
   = help: symbol names must be unique across all files; for example, "a2.proto"
           declares `pkgname.Svc` but it is not directly imported

encountered 3 errors
