fix concurrency issues in Compiler.Compile and Value.Source

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

dagger/compiler.go

@@ -48,6 +48,9 @@ func (cc *Compiler) EmptyStruct() (*Value, error) {
 }
 
 func (cc *Compiler) Compile(name string, src interface{}) (*Value, error) {
+	cc.Lock()
+	defer cc.Unlock()
+
 	inst, err := cc.Cue().Compile(name, src)
 	if err != nil {
 		// FIXME: cleaner way to unwrap cue error details?

dagger/value.go

@@ -255,6 +255,9 @@ func (v *Value) Validate(defs ...string) error {
 
 // Return cue source for this value
 func (v *Value) Source() ([]byte, error) {
+	v.cc.RLock()
+	defer v.cc.RUnlock()
+
 	return cueformat.Node(v.val.Eval().Syntax())
 }