cmd/go: set GoVersion for files on the command line with vet

For: #65612
Fixes: #66092

For now, we will align the behavior such that vet and the compiler agree
that gover.Local() will be used for command-line-files.

We expect to change this to set the goversion as the containing module's go
version.

Change-Id: If7f2ea3a82e8e876716f18dacc021026de175a93
Reviewed-on: https://go-review.googlesource.com/c/go/+/593156
Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Sam Thanawalla <samthanawalla@google.com>

src/cmd/go/internal/work/exec.go

@@ -1180,6 +1180,7 @@ func buildVetConfig(a *Action, srcfiles []string) {
 		PackageFile:  make(map[string]string),
 		Standard:     make(map[string]bool),
 	}
+	vcfg.GoVersion = "go" + gover.Local()
 	if a.Package.Module != nil {
 		v := a.Package.Module.GoVersion
 		if v == "" {

src/cmd/go/internal/work/gc.go

@@ -66,15 +66,18 @@ func (gcToolchain) gc(b *Builder, a *Action, archive string, importcfg, embedcfg
 
 	pkgpath := pkgPath(a)
 	defaultGcFlags := []string{"-p", pkgpath}
+	vers := gover.Local()
 	if p.Module != nil {
 		v := p.Module.GoVersion
 		if v == "" {
 			v = gover.DefaultGoModVersion
 		}
+		// TODO(samthanawalla): Investigate when allowedVersion is not true.
 		if allowedVersion(v) {
-			defaultGcFlags = append(defaultGcFlags, "-lang=go"+gover.Lang(v))
+			vers = v
 		}
 	}
+	defaultGcFlags = append(defaultGcFlags, "-lang=go"+gover.Lang(vers))
 	if p.Standard {
 		defaultGcFlags = append(defaultGcFlags, "-std")
 	}

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

@@ -0,0 +1,10 @@
+# go.dev/issue/66092
+# This test ensures that files listed on the commandline will pass
+# the language version to the compiler.
+# All compilations should specify some -lang.
+
+go build -n x.go
+stderr '-lang=go1\.[0-9]+'
+
+-- x.go --
+package main

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

@@ -0,0 +1,43 @@
+# go.dev/issue/65612
+# go vet should set the GoVersion for command line files.
+
+env TESTGO_VERSION=go1.22.1
+env TESTGO_VERSION_SWITCH=switch
+
+go vet -n -json example.com/m
+stderr '"GoVersion": "go1.22.0"'
+
+# A command line file should use the local go version.
+go vet -n -json main.go
+stderr '"GoVersion": "go1.22.1"'
+
+# In workspace mode, the command line file version should use go.work version.
+cp go.work.orig go.work
+go vet -n -json example.com/m
+stderr '"GoVersion": "go1.22.0'
+
+go vet -n -json main.go
+stderr '"GoVersion": "go1.22.2'
+
+# Without go.mod or go.work, the command line file version should use local go version .
+env TESTGO_VERSION=go1.22.3
+rm go.mod
+rm go.work
+
+! go vet -n -json example.com/m
+
+go vet -n -json main.go
+stderr '"GoVersion": "go1.22.3"'
+
+-- go.mod --
+module example.com/m
+
+go 1.22.0
+
+-- go.work.orig --
+go 1.22.2
+
+use .
+
+-- main.go --
+package main