cmd/cue: add testscript reproducing get go issues with std packages

For #648.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I5b5f54a3b859e1e55b8bd80f3cf1943ee841e1ba
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1210515
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mvdan

cmd/cue/cmd/testdata/script/get_go_std.txtar

@@ -0,0 +1,86 @@
+# Go standard library packages can cause issues, because we cannot generate
+# packages such as cue.mod/gen/time which conflict with our own standard library.
+
+exec cue get go --local
+cmp src_go_gen.cue src_go_gen.cue.golden
+
+# Check which files were generated under cue.mod/gen and other directories.
+# TODO: we should be generating zero "std" packages under cue.mod/gen.
+find-files cue.mod
+stdout '^cue.mod/gen/[^.]+/'
+
+# Verify that the result can be loaded correctly.
+# TODO: this should succeed, not fail.
+! exec cue vet -c=false
+cmp stderr vet.stderr
+
+-- go.mod --
+module mod.test
+
+go 1.21
+-- cue.mod/module.cue --
+module: "mod.test"
+
+language: version: "v0.12.0"
+-- src.go --
+package x
+
+import (
+	"io"
+	"reflect"
+	"time"
+)
+
+type Root struct {
+	// reflect types and values in Go are opaque and do not encode as useful JSON.
+	ReflectType  reflect.Type
+	ReflectValue reflect.Value
+
+	// reflect.ValueError is an example of a struct made up of simple types,
+	// in this case a Method string and a Kind uint. We could generate that structure,
+	// as long as we don't place it in cue.mod/pkg/reflect, conflicting with CUE's own std.
+	ReflectValueError reflect.ValueError
+
+	// io.Writer is an interface, so there is no structure to be generated.
+	// Moreover, even though "io" is a very common Go package, CUE has no such package.
+	IoWriter io.Writer
+
+	// time.Month is just an int type, but this edge case is particularly interesting
+	// given that CUE already has a "time" package with e.g. Duration and Time, but no Month.
+	TimeMonth time.Month
+}
+-- src_go_gen.cue.golden --
+// Code generated by cue get go. DO NOT EDIT.
+
+//cue:generate cue get go mod.test
+
+package x
+
+import (
+	"reflect"
+	"io"
+	"time"
+)
+
+#Root: {
+	// reflect types and values in Go are opaque and do not encode as useful JSON.
+	ReflectType: reflect.#Type
+
+	// reflect.ValueError is an example of a struct made up of simple types,
+	// in this case a Method string and a Kind uint. We could generate that structure,
+	// as long as we don't place it in cue.mod/pkg/reflect, conflicting with CUE's own std.
+	ReflectValueError: reflect.#ValueError
+
+	// io.Writer is an interface, so there is no structure to be generated.
+	// Moreover, even though "io" is a very common Go package, CUE has no such package.
+	IoWriter: io.#Writer
+
+	// time.Month is just an int type, but this edge case is particularly interesting
+	// given that CUE already has a "time" package with e.g. Duration and Time, but no Month.
+	TimeMonth: time.#Month
+}
+-- vet.stderr --
+builtin package "reflect" undefined:
+    ./src_go_gen.cue:8:2
+builtin package "io" undefined:
+    ./src_go_gen.cue:9:2