cmd/go: PackageVetx in vet.cfg should list only immediate dependencies.

Updates #30296

Change-Id: Ifea1a4c82c1c5b31fdc2e96fdbb1274748c8f50e
Reviewed-on: https://go-review.googlesource.com/c/go/+/164459Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/work/action.go

@@ -423,7 +423,7 @@ func (b *Builder) vetAction(mode, depMode BuildMode, p *load.Package) *Action {
 		} else {
 			deps = []*Action{a1, aFmt}
 		}
-		for _, p1 := range load.PackageList(p.Internal.Imports) {
+		for _, p1 := range p.Internal.Imports {
 			deps = append(deps, b.vetAction(mode, depMode, p1))
 		}
 

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

+env GO111MODULE=off
+
+# Issue 30296. Verify that "go vet" uses only immediate dependencies.
+
+# First run fills the cache.
+go vet a
+
+go vet -x a
+! stderr 'transitive'
+
+-- a/a.go --
+package a
+
+import "b"
+
+func F() {
+	b.F()
+}
+
+-- b/b.go --
+package b
+
+import "transitive"
+
+func F() {
+	transitive.F()
+}
+
+-- transitive/c.go --
+package transitive
+
+func F() {
+}
+