cmd/go/internal/modload: ignore selected version in checkRetractions

Fixes #42601

Change-Id: I58d817ed34ccbd39591326c4bc23569f94028412
Reviewed-on: https://go-review.googlesource.com/c/go/+/272006
Run-TryBot: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/modload/modfile.go

@@ -114,9 +114,9 @@ func CheckRetractions(ctx context.Context, m module.Version) error {
 
 		// Find the latest version of the module.
 		// Ignore exclusions from the main module's go.mod.
-		// We may need to account for the current version: for example,
-		// v2.0.0+incompatible is not "latest" if v1.0.0 is current.
-		rev, err := Query(ctx, path, "latest", Selected(path), nil)
+		const ignoreSelected = ""
+		var allowAll AllowedFunc
+		rev, err := Query(ctx, path, "latest", ignoreSelected, allowAll)
 		if err != nil {
 			return &entry{nil, err}
 		}

src/cmd/go/testdata/mod/example.com_retract_incompatible_v1.0.0.txt

@@ -0,0 +1,19 @@
+The v1.0.0 release of example.com/retract/incompatible retracts
+v2.0.0+incompatible.
+
+-- .mod --
+module example.com/retract/incompatible
+
+go 1.16
+
+retract v2.0.0+incompatible
+-- .info --
+{"Version":"v1.0.0"}
+-- go.mod --
+module example.com/retract/incompatible
+
+go 1.16
+
+retract v2.0.0+incompatible
+-- incompatible.go --
+package incompatible

src/cmd/go/testdata/mod/example.com_retract_incompatible_v2.0.0+incompatible.txt

@@ -0,0 +1,9 @@
+The v1.0.0 release of example.com/retract/incompatible retracts
+v2.0.0+incompatible.
+
+-- .mod --
+module example.com/retract/incompatible
+-- .info --
+{"Version":"v2.0.0+incompatible"}
+-- incompatible.go --
+package incompatible

src/cmd/go/testdata/script/mod_retract_incompatible.txt

@@ -0,0 +1,15 @@
+# The current version of a module should not be considered when loading
+# retractions. If the current version is +incompatible, we should not prefer
+# +incompatible versions when looking for retractions.
+# Verifies #42601.
+
+go mod init m
+
+# Request a +incompatible version retracted in v1.0.0.
+go get -d example.com/retract/incompatible@v2.0.0+incompatible
+stderr '^go: warning: example.com/retract/incompatible@v2.0.0\+incompatible: retracted by module author$'
+
+# We should still see a warning if the +incompatible was previously in the
+# build list.
+go get -d example.com/retract/incompatible@v2.0.0+incompatible
+stderr '^go: warning: example.com/retract/incompatible@v2.0.0\+incompatible: retracted by module author$'