gimports is a simple tool to operate as something of an inverse of "go list". It reports by package which source files in a dir tree import that package.
For example, if you want to know which go source files under a directory tree import the errors package from the standard library, you could run:
$ gimports path/to/src/tree errors
You would get output something like this:
IMPORTERS OF "errors":
../openssl/examples/evpexpl/main.go
../openssl/ssl/httpsclient.go
../webster/webster.go
If you omit the package name, then gimports will report the imports for all files under the tree by package.
For more detailed reporting, you can call gimports -calls <dir> [<package>] - this will trigger the per-file reporting of all function calls by package (or for the specific package if named on the command line):
IMPORTERS of net/http (2 results):
../webster/webster.go
Line: 25 http.Response
Line: 76 http.Response
Line: 84 http.Client
../webster/webster_types.go
Line: 9 http.Client