internal/api: implement package imported-by endpoint

- Implement ServePackageImportedBy handler and GetImportedBy and GetImportedByCount datasource methods.

Change-Id: I8c4cc65fbff7172eaf48e5426e4f3f41c82bd38e
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/754865
Reviewed-by: Jonathan Amsterdam <jba@google.com>
kokoro-CI: kokoro <noreply+kokoro@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ethan Lee <ethanalee@google.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/internal/fetchdatasource/fetchdatasource.go b/internal/fetchdatasource/fetchdatasource.go
index dfe30fc9..af03c733 100644
--- a/internal/fetchdatasource/fetchdatasource.go
+++ b/internal/fetchdatasource/fetchdatasource.go
@@ -436,3 +436,13 @@ func (ds *FetchDataSource) GetSymbols(ctx context.Context, pkgPath, modulePath,
 	}
 	return doc.API, nil
 }
+
+// GetImportedBy is not implemented.
+func (ds *FetchDataSource) GetImportedBy(ctx context.Context, pkgPath, modulePath string, limit int) ([]string, error) {
+	return nil, nil
+}
+
+// GetImportedByCount is not implemented.
+func (ds *FetchDataSource) GetImportedByCount(ctx context.Context, pkgPath, modulePath string) (int, error) {
+	return 0, nil
+}