Always import non-weak imported proto packages.

This is required so we get the transitive closure of proto types.

This has negligible impact on generated binary sizes.

protoc-gen-go/generator/generator.go

@@ -1271,15 +1271,14 @@ func (g *Generator) generateImports() {
 			g.P("// skipping weak import ", fd.PackageName(), " ", strconv.Quote(importPath))
 			continue
 		}
-		if _, ok := g.usedPackages[fd.PackageName()]; ok {
-			g.P("import ", fd.PackageName(), " ", strconv.Quote(importPath))
-		} else {
-			// TODO: Re-enable this when we are more feature-complete.
-			// For instance, some protos use foreign field extensions, which we don't support.
-			// Until then, this is just annoying spam.
-			//log.Printf("protoc-gen-go: discarding unused import from %v: %v", *g.file.Name, s)
-			g.P("// discarding unused import ", fd.PackageName(), " ", strconv.Quote(importPath))
-		}
+		// We need to import all the dependencies, even if we don't reference them,
+		// because other code and tools depend on having the full transitive closure
+		// of protocol buffer types in the binary.
+		pname := fd.PackageName()
+		if _, ok := g.usedPackages[pname]; !ok {
+			pname = "_"
+		}
+		g.P("import ", pname, " ", strconv.Quote(importPath))
 	}
 	g.P()
 	// TODO: may need to worry about uniqueness across plugins

protoc-gen-go/testdata/Makefile

@@ -40,6 +40,9 @@ test:	golden testbuild
 #	./extension_test
 #	@echo PASS
 
+my_test/test.pb.go: my_test/test.proto
+	protoc --go_out=Mmulti/multi1.proto=github.com/golang/protobuf/protoc-gen-go/testdata/multi:. $<
+
 golden:
 	make -B my_test/test.pb.go
 	diff -w my_test/test.pb.go my_test/test.pb.go.golden

protoc-gen-go/testdata/golden_test.go

@@ -73,7 +73,7 @@ func TestGolden(t *testing.T) {
 	// Compute the original checksum.
 	goldenSum := sum(t, "my_test/test.pb.go")
 	// Run the proto compiler.
-	run(t, "protoc", "--go_out="+os.TempDir(), "my_test/test.proto")
+	run(t, "protoc", "--go_out=Mmulti/multi1.proto=github.com/golang/protobuf/protoc-gen-go/testdata/multi:"+os.TempDir(), "my_test/test.proto")
 	newFile := filepath.Join(os.TempDir(), "my_test/test.pb.go")
 	defer os.Remove(newFile)
 	// Compute the new checksum.

protoc-gen-go/testdata/main_test.go

@@ -36,8 +36,8 @@ package testdata
 import (
 	"testing"
 
-	multipb "./multi"
 	mytestpb "./my_test"
+	multipb "github.com/golang/protobuf/protoc-gen-go/testdata/multi"
 )
 
 func TestLink(t *testing.T) {

protoc-gen-go/testdata/my_test/test.pb.go

@@ -24,8 +24,7 @@ package my_test
 import proto "github.com/golang/protobuf/proto"
 import fmt "fmt"
 import math "math"
-
-// discarding unused import multitest2 "multi"
+import _ "github.com/golang/protobuf/protoc-gen-go/testdata/multi"
 
 // Reference imports to suppress errors if they are not otherwise used.
 var _ = proto.Marshal

protoc-gen-go/testdata/my_test/test.pb.go.golden

@@ -24,8 +24,7 @@ package my_test
 import proto "github.com/golang/protobuf/proto"
 import fmt "fmt"
 import math "math"
-
-// discarding unused import multitest2 "multi"
+import _ "github.com/golang/protobuf/protoc-gen-go/testdata/multi"
 
 // Reference imports to suppress errors if they are not otherwise used.
 var _ = proto.Marshal