cmd/go/internal/modload: fix (*mvsReqs).Max when the second argument is the empty...

As far as I can tell, this bug had gone unnoticed because everything
that uses Max so far happened to only ever present the empty string as
the first argument.

For #37438

Change-Id: Ie8c42313157d2c2c17e4058c53b5bb026b95a1c1
Reviewed-on: https://go-review.googlesource.com/c/go/+/266860
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>

diff --git a/src/cmd/go/internal/modload/mvs.go b/src/cmd/go/internal/modload/mvs.go
index 94373bc5f39936ac705745bed2c2219920756029..045cbead3b2b17ded7d28685a4d8cd2267c87a6e 100644 (file)
--- a/src/cmd/go/internal/modload/mvs.go
+++ b/src/cmd/go/internal/modload/mvs.go
@@ -58,7 +58,7 @@ func (r *mvsReqs) Required(mod module.Version) ([]module.Version, error) {
 // be chosen over other versions of the same module in the module dependency
 // graph.
 func (*mvsReqs) Max(v1, v2 string) string {
-       if v1 != "" && semver.Compare(v1, v2) == -1 {
+       if v1 != "" && (v2 == "" || semver.Compare(v1, v2) == -1) {
                return v2
        }
        return v1

diff --git a/src/cmd/go/internal/modload/mvs_test.go b/src/cmd/go/internal/modload/mvs_test.go
new file mode 100644 (file)
index 0000000..0cb376e
--- /dev/null
+++ b/src/cmd/go/internal/modload/mvs_test.go
@@ -0,0 +1,33 @@
+// 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 modload_test
+
+import (
+       "testing"
+
+       "cmd/go/internal/modload"
+)
+
+func TestReqsMax(t *testing.T) {
+       type testCase struct {
+               a, b, want string
+       }
+       reqs := modload.Reqs()
+       for _, tc := range []testCase{
+               {a: "v0.1.0", b: "v0.2.0", want: "v0.2.0"},
+               {a: "v0.2.0", b: "v0.1.0", want: "v0.2.0"},
+               {a: "", b: "v0.1.0", want: ""}, // "" is Target.Version
+               {a: "v0.1.0", b: "", want: ""},
+               {a: "none", b: "v0.1.0", want: "v0.1.0"},
+               {a: "v0.1.0", b: "none", want: "v0.1.0"},
+               {a: "none", b: "", want: ""},
+               {a: "", b: "none", want: ""},
+       } {
+               max := reqs.Max(tc.a, tc.b)
+               if max != tc.want {
+                       t.Errorf("Reqs().Max(%q, %q) = %q; want %q", tc.a, tc.b, max, tc.want)
+               }
+       }
+}