internal/tests: add a dependency test for cmd/pkgsite

Ensuring that it keeps its limited set of dependencies.
The test is rather slow: it takes about 5 seconds for me. I tried
parallelizing it and only got it down to about 3 seconds so I figured
it wasn't worth it.

For golang/go#61399

Change-Id: I34b75a1f77480e02368ddb7d552e89ab106bf28e
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/551515
LUCI-TryBot-Result: Go LUCI <[email protected]>
kokoro-CI: kokoro <[email protected]>
Reviewed-by: Jonathan Amsterdam <[email protected]>

Author: matloob

internal/tests/deps/cmd_pkgsite_deps_test.go

@@ -0,0 +1,69 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// deps_test tests dependencies of cmd/pkgsite are kept to a limited set.
+package deps_test
+
+import (
+	"os/exec"
+	"strings"
+	"testing"
+)
+
+// non-test packages are allowed to depend on licensecheck and safehtml, x/ repos, and markdown.
+var allowedModDeps = map[string]bool{
+	"github.com/google/licensecheck": true,
+	"github.com/google/safehtml":     true,
+	"golang.org/x/mod":               true,
+	"golang.org/x/net":               true,
+	"golang.org/x/pkgsite":           true,
+	"golang.org/x/sync":              true,
+	"golang.org/x/text":              true,
+	"golang.org/x/tools":             true,
+	"rsc.io/markdown":                true,
+}
+
+// test packages are also allowed to depend on go-cmp
+var additionalAllowedTestModDeps = map[string]bool{
+	"github.com/google/go-cmp": true,
+}
+
+func TestCmdPkgsiteDeps(t *testing.T) {
+	// First, list all dependencies of pkgsite.
+	out, err := exec.Command("go", "list", "-deps", "golang.org/x/pkgsite/cmd/pkgsite").Output()
+	if err != nil {
+		t.Fatal("running go list: ", err)
+	}
+	pkgs := strings.Fields(string(out))
+	for _, pkg := range pkgs {
+		// Filter to only the dependencies that are in the pkgsite module.
+		if !strings.HasPrefix(pkg, "golang.org/x/pkgsite") {
+			continue
+		}
+
+		// Get the test module deps and check them against allowedTestModDeps.
+		out, err := exec.Command("go", "list", "-deps", "-test", "-f", "{{if .Module}}{{.Module.Path}}{{end}}", pkg).Output()
+		if err != nil {
+			t.Fatal(err)
+		}
+		testmodules := strings.Fields(string(out))
+		for _, m := range testmodules {
+			if !(allowedModDeps[m] || additionalAllowedTestModDeps[m]) {
+				t.Fatalf("disallowed test module dependency %q found through %q", m, pkg)
+			}
+		}
+
+		// Get the module deps and check them against allowedModDeps
+		out, err = exec.Command("go", "list", "-deps", "-f", "{{if .Module}}{{.Module.Path}}{{end}}", pkg).Output()
+		if err != nil {
+			t.Fatal(err)
+		}
+		modules := strings.Fields(string(out))
+		for _, m := range modules {
+			if !allowedModDeps[m] {
+				t.Fatalf("disallowed module dependency %q found through %q", m, pkg)
+			}
+		}
+	}
+}