protoc-gen-go: stop generating package "// import" comment

Usage of the import comment is being deprecated in favor of a go.mod
file as the Go ecosystem moves towards modules.

Fixes #678

protoc-gen-go/generator/generator.go

@@ -1208,12 +1208,7 @@ func (g *Generator) generateHeader() {
 	}
 	g.P()
 
-	importPath, _, _ := g.file.goPackageOption()
-	if importPath == "" {
-		g.P("package ", g.file.packageName)
-	} else {
-		g.P("package ", g.file.packageName, " // import ", GoImportPath(g.ImportPrefix)+importPath)
-	}
+	g.P("package ", g.file.packageName)
 	g.P()
 
 	if loc, ok := g.file.comments[strconv.Itoa(packagePath)]; ok {

protoc-gen-go/golden_test.go

@@ -3,7 +3,6 @@ package main
 import (
 	"bytes"
 	"flag"
-	"fmt"
 	"go/build"
 	"go/parser"
 	"go/token"
@@ -150,7 +149,7 @@ func TestParameters(t *testing.T) {
 		wantPackageB: "test_beta",
 		wantImportsA: map[string]bool{
 			"github.com/golang/protobuf/proto": true,
-			"beta": true,
+			"beta":                             true,
 		},
 	}, {
 		parameters: "import_prefix=prefix",
@@ -323,64 +322,6 @@ func TestParameters(t *testing.T) {
 	}
 }
 
-func TestPackageComment(t *testing.T) {
-	workdir, err := ioutil.TempDir("", "proto-test")
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer os.RemoveAll(workdir)
-
-	var packageRE = regexp.MustCompile(`(?m)^package .*`)
-
-	for i, test := range []struct {
-		goPackageOption string
-		wantPackage     string
-	}{{
-		goPackageOption: ``,
-		wantPackage:     `package proto_package`,
-	}, {
-		goPackageOption: `option go_package = "go_package";`,
-		wantPackage:     `package go_package`,
-	}, {
-		goPackageOption: `option go_package = "import/path/of/go_package";`,
-		wantPackage:     `package go_package // import "import/path/of/go_package"`,
-	}, {
-		goPackageOption: `option go_package = "import/path/of/something;go_package";`,
-		wantPackage:     `package go_package // import "import/path/of/something"`,
-	}, {
-		goPackageOption: `option go_package = "import_path;go_package";`,
-		wantPackage:     `package go_package // import "import_path"`,
-	}} {
-		srcName := filepath.Join(workdir, fmt.Sprintf("%d.proto", i))
-		tgtName := filepath.Join(workdir, fmt.Sprintf("%d.pb.go", i))
-
-		buf := &bytes.Buffer{}
-		fmt.Fprintln(buf, `syntax = "proto3";`)
-		fmt.Fprintln(buf, `package proto_package;`)
-		fmt.Fprintln(buf, test.goPackageOption)
-		if err := ioutil.WriteFile(srcName, buf.Bytes(), 0666); err != nil {
-			t.Fatal(err)
-		}
-
-		protoc(t, []string{"-I" + workdir, "--go_out=paths=source_relative:" + workdir, srcName})
-
-		out, err := ioutil.ReadFile(tgtName)
-		if err != nil {
-			t.Fatal(err)
-		}
-
-		pkg := packageRE.Find(out)
-		if pkg == nil {
-			t.Errorf("generated .pb.go contains no package line\n\nsource:\n%v\n\noutput:\n%v", buf.String(), string(out))
-			continue
-		}
-
-		if got, want := string(pkg), test.wantPackage; got != want {
-			t.Errorf("unexpected package statement with go_package = %q\n got: %v\nwant: %v", test.goPackageOption, got, want)
-		}
-	}
-}
-
 // parseFile returns a file's package name and a list of all packages it imports.
 func parseFile(source string) (packageName string, imports []string, err error) {
 	fset := token.NewFileSet()