vend: Correctly copy replaced modules to their replacement directory.

file/file.go

@@ -34,7 +34,7 @@ dep:
 }
 
 // CopyModuleDependencies copies module level dependencies transitively.
-func CopyModuleDependencies(deps []Dep) {
+func CopyModuleDependencies(mod GoMod, deps []Dep) {
 	modFile := cli.ReadModFile(vendorDir())
 	deleteVendorDir()
 
@@ -44,6 +44,14 @@ func CopyModuleDependencies(deps []Dep) {
 		copy(d.Dir, dest)
 	}
 
+	for _, d := range mod.Replace {
+		if d.Old.Path != d.New.Path {
+			src := path.Join(vendorDir(), d.New.Path)
+			dest := path.Join(vendorDir(), d.Old.Path)
+			copy(src, dest)
+		}
+	}
+
 	SaveReport(modFile)
 }
 

main.go

@@ -16,15 +16,13 @@ func main() {
 		cli.UpdateModule()
 		json := cli.ReadDownloadJSON()
 		deps := file.ParseDownloadJSON(json)
+		json = cli.ReadModJSON()
+		mod := file.ParseModJSON(json)
 
 		if options.PkgOnly {
-			json = cli.ReadModJSON()
-			mod := file.ParseModJSON(json)
-
 			file.CopyPkgDependencies(mod, deps)
 		} else {
-
-			file.CopyModuleDependencies(deps)
+			file.CopyModuleDependencies(mod, deps)
 		}
 	}
 }