I have an idea for a fix for this problem

diff --git a/go/analysis/passes/copylock/copylock.go b/go/analysis/passes/copylock/copylock.go
index c4ebf785..e856a14c 100644
--- a/go/analysis/passes/copylock/copylock.go
+++ b/go/analysis/passes/copylock/copylock.go
@@ -252,6 +252,17 @@ func lockPath(tpkg *types.Package, typ types.Type) typePath {
                typ = atyp.Elem()
        }
 
+       ttyp, ok := typ.Underlying().(*types.Tuple)
+       if ok {
+               for i := 0; i < ttyp.Len(); i++ {
+                       subpath := lockPath(tpkg, ttyp.At(i).Type())
+                       if subpath != nil {
+                               return append(subpath, typ)
+                       }
+               }
+               return nil
+       }
+

But I could use some help with directions on how to test the solution. I have stepped through it using dlv and it seems to do the right thing but some pointers for writing and running the unit tests would be helpful.

@ajwans: You should be able to run the unit tests by running the copylock_test in the copylock directory. The test cases themselves can be found here: https://github.com/golang/tools/tree/master/go/analysis/passes/copylock/testdata/src/a. Each want comment indicates a diagnostic that should be reported at the given line, so you can add your repro case to one of those files and add a // want diagnostic where you expect it to add a test case.

It would be good to also test this change on functions returning multiple values. Function returns can be a bit tricky: https://github.com/golang/tools/blob/master/go/analysis/passes/copylock/copylock.go#L162-L165

Tests for these could go in:
https://github.com/golang/tools/blob/master/go/analysis/passes/copylock/testdata/src/a/copylock_func.go

It would be good to also test this change on functions returning multiple values. Function returns can be a bit tricky: https://github.com/golang/tools/blob/master/go/analysis/passes/copylock/copylock.go#L162-L165

Tests for these could go in:
https://github.com/golang/tools/blob/master/go/analysis/passes/copylock/testdata/src/a/copylock_func.go

I looked into making this suggested change. It looks like this case is already considered and handled. The comments at copylocks.go:162 & copylocks.go:228 indicate that it not an error because a function is allowed to return a T{} with an empty lock.

I created a PR for this golang/tools#319

golang/tools#319 has been merged and I think this issue can be closed. (the referenced issue in the Fixes line is Fixes #45896).

Looks closed to me too. I believe the Fixes #45896 message was just mis formatted for the gopherbot on an x/tools change.