tests: nogo over generated code

This add a test that demonstrate the current behavior of nogo today:
code which was generated under rules_go during internal/external test
package compilation is subjected to static analysis.

This behavior is not ideal as end users have very little control over
the way rules_go generated these code and would not be able to fix them
to please the analyzer.

In a future patch, we will introduce a mechanism to alleviate this pain
and flip the expectation in this test.

tests/core/nogo/generate/BUILD.bazel

@@ -0,0 +1,6 @@
+load("@io_bazel_rules_go//go/tools/bazel_testing:def.bzl", "go_bazel_test")
+
+go_bazel_test(
+    name = "empty_test",
+    srcs = ["empty_test.go"],
+)

tests/core/nogo/generate/README.rst

@@ -0,0 +1,12 @@
+nogo test with generated code
+=======================
+
+.. _nogo: /go/nogo.rst
+
+Tests to ensure `nogo`_ interaction with generated code.
+
+empty_test
+-------------
+Checks that `nogo`_ is running over the `_empty.go` file that was
+generated as part of GoCompilePkg.
+

tests/core/nogo/generate/empty_test.go

@@ -0,0 +1,116 @@
+// Copyright 2019 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package empty_test
+
+import (
+	"errors"
+	"os/exec"
+	"strings"
+	"testing"
+
+	"github.com/bazelbuild/rules_go/go/tools/bazel_testing"
+)
+
+func TestMain(m *testing.M) {
+	bazel_testing.TestMain(m, bazel_testing.Args{
+		Main: `
+-- BUILD.bazel --
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test", "nogo")
+
+go_test(
+    name = "simple_test",
+    size = "small",
+    srcs = ["simple_test.go"],
+)
+
+nogo(
+    name = "nogo",
+    deps = ["//noempty"],
+    visibility = ["//visibility:public"],
+)
+-- simple_test.go --
+package simple
+
+import (
+	"testing"
+)
+
+func TestFoo(t *testing.T) {
+}
+-- noempty/BUILD.bazel --
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "noempty",
+    srcs = ["analyzer.go"],
+    importpath = "noempty",
+    visibility = ["//visibility:public"],
+    deps = [
+        "@org_golang_x_tools//go/analysis",
+    ],
+)
+-- noempty/analyzer.go --
+package noempty
+
+import (
+	"fmt"
+	"path/filepath"
+	"strings"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var Analyzer = &analysis.Analyzer{
+	Name:     "noempty",
+	Doc:      "noempty ensure that source code was not a generated file created by rules_go test rewrite",
+	Run:      run,
+}
+
+func run(pass *analysis.Pass) (interface{}, error) {
+	for _, f := range pass.Files {
+		pos := pass.Fset.PositionFor(f.Pos(), false)
+
+		if strings.HasSuffix(pos.Filename, filepath.Join(".", "_empty.go")) {
+			pass.Report(analysis.Diagnostic{
+				Pos:     0,
+				Message: fmt.Sprintf("Detected generated source code from rules_go: %s", pos.Filename),
+			})
+		}
+	}
+
+	return nil, nil
+}
+`,
+		Nogo: `@//:nogo`,
+	})
+}
+
+func TestNogoGenEmptyCode(t *testing.T) {
+	out, err := bazel_testing.BazelOutput("build", "-k", "//:simple_test")
+	if err == nil {
+		t.Fatal("test should fail")
+	}
+
+	var eErr *exec.ExitError
+	if errors.As(err, &eErr) &&
+		strings.Contains(string(eErr.Stderr), "Detected generated source code from rules_go") &&
+		strings.Contains(string(eErr.Stderr), "(noempty)") {
+		// Expected failure
+		return
+	}
+
+	println(string(out))
+	t.Fatal(err)
+}