lsp: add simple workspace-based test for basic CUE module

This is in preparation for later CLs which enforce that a workspace
folder must correspond to the root of a CUE module.

Also add a build constraint to prevent workspace folder tests running on
Windows. In a later CL this becomes relevant because a message shown to
the user includes a directory path. Fixing this is tracked by
https://cuelang.org/issue/2752.

Signed-off-by: Paul Jolly <paul@myitcv.io>
Change-Id: Id3cad53160f4de6360c9d9866a2291dca567bc42
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1206615
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

cmd/cue/cmd/integration/workspace/workspace_folders_test.go

@@ -1,16 +1,46 @@
+//go:build !windows
+
 package workspace
 
 import (
 	"testing"
 
 	"cuelang.org/go/internal/golangorgx/gopls/hooks"
 	. "cuelang.org/go/internal/golangorgx/gopls/test/integration"
+	"cuelang.org/go/internal/golangorgx/gopls/test/integration/fake"
+	"github.com/go-quicktest/qt"
 )
 
 func TestMain(m *testing.M) {
 	Main(m, hooks.Options)
 }
 
+// TestWorkingSimpleModule ensures that we have a successful package load for a
+// simple module rooted in the workspace folder with a single CUE file at the
+// root.
+func TestWorkingSimpleModule(t *testing.T) {
+	const files = `
+-- cue.mod/module.cue --
+module: "mod.example"
+language: {
+        version: "v0.11.0"
+}
+-- a.cue --
+package a
+-- b/b.cue --
+package c
+`
+	WithOptions().Run(t, files, func(t *testing.T, env *Env) {
+		// Simulate a change and ensure we get diagnostics back
+		env.OpenFile("a.cue")
+		env.EditBuffer("a.cue", fake.NewEdit(1, 0, 1, 0, "\nx: 5\n"))
+		got := env.BufferText("a.cue")
+		want := "package a\n\nx: 5\n"
+		qt.Assert(t, qt.Equals(got, want))
+		env.Await(env.DoneWithChange())
+	})
+}
+
 // TestMultipleWorkspaceFolders verifies the behaviour of starting 'cue lsp'
 // with multiple WorkspaceFolders. This is currently not supported, and hence
 // the test is a negative test that asserts 'cue lsp' will fail (during the