cmd/go: add dark copy of golang.org/x/vgo

This CL corresponds to golang.org/cl/118096 (7fbc8df48a7)
in the vgo repo.

It copies the bulk of the code from vgo back into the main repo,
but completely disabled - vgo.Init is a no-op and vgo.Enabled
returns false unconditionally.

The point of this CL is to make the two trees easier to diff and
to make future syncs smaller.

Change-Id: Ic34fd5ddd8272a70c5a3b3437b5169e967d0ed03
Reviewed-on: https://go-review.googlesource.com/118095
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 377 insertions, 0 deletions

diff --git a/src/cmd/go/internal/mvs/mvs_test.go b/src/cmd/go/internal/mvs/mvs_test.go
new file mode 100644
index 0000000000..0fd55e4e45
--- /dev/null
+++ b/src/cmd/go/internal/mvs/mvs_test.go
@@ -0,0 +1,377 @@
+// Copyright 2018 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 mvs
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+
+	"cmd/go/internal/module"
+)
+
+var tests = `
+# Scenario from blog.
+name: blog
+A: B1 C2
+B1: D3
+C1: D2
+C2: D4
+C3: D5
+C4: G1
+D2: E1
+D3: E2
+D4: E2 F1
+D5: E2
+G1: C4
+A2: B1 C4 D4
+build A: A B1 C2 D4 E2 F1
+upgrade* A: A B1 C4 D5 E2 G1
+upgrade A C4: A B1 C4 D4 E2 F1 G1
+downgrade A2 D2: A2 C4 D2
+
+name: trim
+A: B1 C2
+B1: D3
+C2: B2
+B2:
+build A: A B2 C2
+
+# Cross-dependency between D and E.
+# No matter how it arises, should get result of merging all build lists via max,
+# which leads to including both D2 and E2.
+
+name: cross1
+A: B C
+B: D1
+C: D2
+D1: E2
+D2: E1
+build A: A B C D2 E2
+
+name: cross1V
+A: B2 C D2 E1
+B1: 
+B2: D1
+C: D2
+D1: E2
+D2: E1
+build A: A B2 C D2 E2
+
+name: cross1U
+A: B1 C
+B1: 
+B2: D1
+C: D2
+D1: E2
+D2: E1
+build A: A B1 C D2 E1
+upgrade A B2: A B2 C D2 E2
+
+name: cross1R
+A: B C 
+B: D2
+C: D1
+D1: E2
+D2: E1
+build A: A B C D2 E2
+
+name: cross1X
+A: B C
+B: D1 E2
+C: D2
+D1: E2
+D2: E1
+build A: A B C D2 E2
+
+name: cross2
+A: B D2
+B: D1
+D1: E2
+D2: E1
+build A: A B D2 E2
+
+name: cross2X
+A: B D2
+B: D1 E2
+C: D2
+D1: E2
+D2: E1
+build A: A B D2 E2
+
+name: cross3
+A: B D2 E1
+B: D1
+D1: E2
+D2: E1
+build A: A B D2 E2
+
+name: cross3X
+A: B D2 E1
+B: D1 E2
+D1: E2
+D2: E1
+build A: A B D2 E2
+
+# Should not get E2 here, because B has been updated
+# not to depend on D1 anymore.
+name: cross4
+A1: B1 D2
+A2: B2 D2
+B1: D1
+B2: D2
+D1: E2
+D2: E1
+build A1: A1 B1 D2 E2
+build A2: A2 B2 D2 E1
+
+# But the upgrade from A1 preserves the E2 dep explicitly.
+upgrade A1 B2: A1 B2 D2 E2
+upgradereq A1 B2: B2 E2
+
+name: cross5
+A: D1
+D1: E2
+D2: E1
+build A: A D1 E2
+upgrade* A: A D2 E2
+upgrade A D2: A D2 E2
+upgradereq A D2: D2 E2
+
+name: cross6
+A: D2
+D1: E2
+D2: E1
+build A: A D2 E1
+upgrade* A: A D2 E2
+upgrade A E2: A D2 E2
+
+name: cross7
+A: B C
+B: D1
+C: E1
+D1: E2
+E1: D2
+build A: A B C D2 E2
+
+name: down1
+A: B2
+B1: C1
+B2: C2
+build A: A B2 C2
+downgrade A C1: A B1
+
+name: down2
+A: B2 E2
+B1:
+B2: C2 F2
+C1:
+D1:
+C2: D2 E2
+D2: B2
+E2: D2
+E1:
+F1:
+downgrade A F1: A B1 E1
+
+name: down3
+A: 
+
+# golang.org/issue/25542.
+name: noprev1
+A: B4 C2
+B2.hidden: 
+C2: 
+downgrade A B2.hidden: A B2.hidden C2
+
+name: noprev2
+A: B4 C2
+B2.hidden: 
+B1: 
+C2: 
+downgrade A B2.hidden: A B2.hidden C2
+
+name: noprev3
+A: B4 C2
+B3: 
+B2.hidden: 
+C2: 
+downgrade A B2.hidden: A B2.hidden C2
+`
+
+func Test(t *testing.T) {
+	var (
+		name string
+		reqs reqsMap
+		fns  []func(*testing.T)
+	)
+	flush := func() {
+		if name != "" {
+			t.Run(name, func(t *testing.T) {
+				for _, fn := range fns {
+					fn(t)
+				}
+			})
+		}
+	}
+	m := func(s string) module.Version {
+		return module.Version{Path: s[:1], Version: s[1:]}
+	}
+	ms := func(list []string) []module.Version {
+		var mlist []module.Version
+		for _, s := range list {
+			mlist = append(mlist, m(s))
+		}
+		return mlist
+	}
+	checkList := func(t *testing.T, desc string, list []module.Version, err error, val string) {
+		if err != nil {
+			t.Fatalf("%s: %v", desc, err)
+		}
+		vs := ms(strings.Fields(val))
+		if !reflect.DeepEqual(list, vs) {
+			t.Errorf("%s = %v, want %v", desc, list, vs)
+		}
+	}
+
+	for _, line := range strings.Split(tests, "\n") {
+		line = strings.TrimSpace(line)
+		if strings.HasPrefix(line, "#") || line == "" {
+			continue
+		}
+		i := strings.Index(line, ":")
+		if i < 0 {
+			t.Fatalf("missing colon: %q", line)
+		}
+		key := strings.TrimSpace(line[:i])
+		val := strings.TrimSpace(line[i+1:])
+		if key == "" {
+			t.Fatalf("missing key: %q", line)
+		}
+		kf := strings.Fields(key)
+		switch kf[0] {
+		case "name":
+			if len(kf) != 1 {
+				t.Fatalf("name takes no arguments: %q", line)
+			}
+			flush()
+			reqs = make(reqsMap)
+			fns = nil
+			name = val
+			continue
+		case "build":
+			if len(kf) != 2 {
+				t.Fatalf("build takes one argument: %q", line)
+			}
+			fns = append(fns, func(t *testing.T) {
+				list, err := BuildList(m(kf[1]), reqs)
+				checkList(t, key, list, err, val)
+			})
+			continue
+		case "upgrade*":
+			if len(kf) != 2 {
+				t.Fatalf("upgrade* takes one argument: %q", line)
+			}
+			fns = append(fns, func(t *testing.T) {
+				list, err := UpgradeAll(m(kf[1]), reqs)
+				checkList(t, key, list, err, val)
+			})
+			continue
+		case "upgradereq":
+			if len(kf) < 2 {
+				t.Fatalf("upgrade takes at least one arguments: %q", line)
+			}
+			fns = append(fns, func(t *testing.T) {
+				list, err := Upgrade(m(kf[1]), reqs, ms(kf[2:])...)
+				if err == nil {
+					list, err = Req(m(kf[1]), list, reqs)
+				}
+				checkList(t, key, list, err, val)
+			})
+			continue
+		case "upgrade":
+			if len(kf) < 2 {
+				t.Fatalf("upgrade takes at least one arguments: %q", line)
+			}
+			fns = append(fns, func(t *testing.T) {
+				list, err := Upgrade(m(kf[1]), reqs, ms(kf[2:])...)
+				checkList(t, key, list, err, val)
+			})
+			continue
+		case "downgrade":
+			if len(kf) < 2 {
+				t.Fatalf("downgrade takes at least one arguments: %q", line)
+			}
+			fns = append(fns, func(t *testing.T) {
+				list, err := Downgrade(m(kf[1]), reqs, ms(kf[1:])...)
+				checkList(t, key, list, err, val)
+			})
+			continue
+		}
+		if len(kf) == 1 && 'A' <= key[0] && key[0] <= 'Z' {
+			var rs []module.Version
+			for _, f := range strings.Fields(val) {
+				r := m(f)
+				if reqs[r] == nil {
+					reqs[r] = []module.Version{}
+				}
+				rs = append(rs, r)
+			}
+			reqs[m(key)] = rs
+			continue
+		}
+		t.Fatalf("bad line: %q", line)
+	}
+	flush()
+}
+
+type reqsMap map[module.Version][]module.Version
+
+func (r reqsMap) Max(v1, v2 string) string {
+	if v1 == "none" {
+		return v2
+	}
+	if v2 == "none" {
+		return v1
+	}
+	if v1 < v2 {
+		return v2
+	}
+	return v1
+}
+
+func (r reqsMap) Latest(path string) (module.Version, error) {
+	var m module.Version
+	for k := range r {
+		if k.Path == path && m.Version < k.Version {
+			m = k
+		}
+	}
+	if m.Path == "" {
+		return module.Version{}, &MissingModuleError{module.Version{Path: path, Version: ""}}
+	}
+	return m, nil
+}
+
+func (r reqsMap) Previous(m module.Version) (module.Version, error) {
+	var p module.Version
+	for k := range r {
+		if k.Path == m.Path && p.Version < k.Version && k.Version < m.Version && !strings.HasSuffix(k.Version, ".hidden") {
+			p = k
+		}
+	}
+	if p.Path == "" {
+		return module.Version{Path: m.Path, Version: "none"}, nil
+	}
+	return p, nil
+}
+
+func (r reqsMap) Required(m module.Version) ([]module.Version, error) {
+	rr, ok := r[m]
+	if !ok {
+		return nil, &MissingModuleError{m}
+	}
+	return rr, nil
+}