cmd/go: add //go:embed support

The final piece of //go:embed support: have the go command stitch
together parsing in go/build, low-level data initialization in cmd/compile,
and the new data structures in package embed, to make the //go:embed
feature actually function.

And test, now that all the pieces are available to work together.

For #41191.
(Issue not fixed: still need to add a tool for use by Bazel.)

Change-Id: Ib1d198345c3b4d557d340f292eda13b984b65d65
Reviewed-on: https://go-review.googlesource.com/c/go/+/243945
Trust: Russ Cox <rsc@golang.org>
Trust: Jay Conrod <jayconrod@google.com>
Trust: Johan Brandhorst <johan.brandhorst@gmail.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Johan Brandhorst <johan.brandhorst@gmail.com>

src/embed/internal/embedtest/embed_test.go

@@ -0,0 +1,103 @@
+// Copyright 2020 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.
+
+package embedtest
+
+import (
+	"embed"
+	"reflect"
+	"testing"
+	"testing/fstest"
+)
+
+//go:embed testdata/h*.txt
+//go:embed c*.txt testdata/g*.txt
+var global embed.FS
+
+//go:embed c*txt
+var concurrency string
+
+//go:embed testdata/g*.txt
+var glass []byte
+
+func testFiles(t *testing.T, f embed.FS, name, data string) {
+	t.Helper()
+	d, err := f.ReadFile(name)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if string(d) != data {
+		t.Errorf("read %v = %q, want %q", name, d, data)
+	}
+}
+
+func testString(t *testing.T, s, name, data string) {
+	t.Helper()
+	if s != data {
+		t.Errorf("%v = %q, want %q", name, s, data)
+	}
+}
+
+func testDir(t *testing.T, f embed.FS, name string, expect ...string) {
+	t.Helper()
+	dirs, err := f.ReadDir(name)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	var names []string
+	for _, d := range dirs {
+		name := d.Name()
+		if d.IsDir() {
+			name += "/"
+		}
+		names = append(names, name)
+	}
+	if !reflect.DeepEqual(names, expect) {
+		t.Errorf("readdir %v = %v, want %v", name, names, expect)
+	}
+}
+
+func TestGlobal(t *testing.T) {
+	testFiles(t, global, "concurrency.txt", "Concurrency is not parallelism.\n")
+	testFiles(t, global, "testdata/hello.txt", "hello, world\n")
+	testFiles(t, global, "testdata/glass.txt", "I can eat glass and it doesn't hurt me.\n")
+
+	if err := fstest.TestFS(global); err != nil {
+		t.Fatal(err)
+	}
+
+	testString(t, concurrency, "concurrency", "Concurrency is not parallelism.\n")
+	testString(t, string(glass), "glass", "I can eat glass and it doesn't hurt me.\n")
+}
+
+func TestLocal(t *testing.T) {
+	//go:embed testdata/k*.txt
+	var local embed.FS
+	testFiles(t, local, "testdata/ken.txt", "If a program is too slow, it must have a loop.\n")
+
+	//go:embed testdata/k*.txt
+	var s string
+	testString(t, s, "local variable s", "If a program is too slow, it must have a loop.\n")
+
+	//go:embed testdata/h*.txt
+	var b []byte
+	testString(t, string(b), "local variable b", "hello, world\n")
+}
+
+func TestDir(t *testing.T) {
+	//go:embed testdata
+	var all embed.FS
+
+	testFiles(t, all, "testdata/hello.txt", "hello, world\n")
+	testFiles(t, all, "testdata/i/i18n.txt", "internationalization\n")
+	testFiles(t, all, "testdata/i/j/k/k8s.txt", "kubernetes\n")
+	testFiles(t, all, "testdata/ken.txt", "If a program is too slow, it must have a loop.\n")
+
+	testDir(t, all, ".", "testdata/")
+	testDir(t, all, "testdata/i", "i18n.txt", "j/")
+	testDir(t, all, "testdata/i/j", "k/")
+	testDir(t, all, "testdata/i/j/k", "k8s.txt")
+}