cue/cmd/cue: hoist placeOrphan from import

Note that this puts the hoisting code at a different
point in the control flow. This seems to disallow
using recursively generated fields, whereas before
this was possible. However, as the generated code
used aliases, there is no loss of functionality.

Other than this a minimum was done to make the
code work.

Change-Id: I9d3436e311537588782361b67c0d5b407518022f
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/5024
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

cmd/cue/cmd/import.go

@@ -388,22 +388,30 @@ func combineExpressions(cmd *Command, pkg, filename string, idx int, objs ...ast
 		}
 	}
 
-	f := &ast.File{}
+	f, err := placeOrphans(cmd, filename, pkg, objs)
+	if err != nil {
+		return err
+	}
 
 	if flagRecursive.Bool(cmd) {
 		h := hoister{fields: map[string]bool{}}
+		h.hoist(f)
+	}
 
-		imports := &ast.ImportDecl{}
-
-		h.hoist(&ast.File{Decls: []ast.Decl{
-			imports,
-			&ast.EmbedDecl{Expr: &ast.ListLit{Elts: objs}},
-		}})
+	b, err := format.Node(f, format.Simplify())
+	if err != nil {
+		return fmt.Errorf("error formatting file: %v", err)
+	}
 
-		if len(imports.Specs) > 0 {
-			f.Decls = append(f.Decls, imports)
-		}
+	if cueFile == "-" {
+		_, err := cmd.OutOrStdout().Write(b)
+		return err
 	}
+	return ioutil.WriteFile(cueFile, b, 0644)
+}
+
+func placeOrphans(cmd *Command, filename, pkg string, objs []ast.Expr) (*ast.File, error) {
+	f := &ast.File{}
 
 	index := newIndex()
 	for i, expr := range objs {
@@ -424,18 +432,18 @@ func combineExpressions(cmd *Command, pkg, filename string, idx int, objs ...ast
 			}
 			inst, err := runtime.CompileExpr(expr)
 			if err != nil {
-				return err
+				return nil, err
 			}
 
 			for _, str := range flagPath.StringArray(cmd) {
-				l, err := parser.ParseExpr("<path flag>", str)
+				l, err := parser.ParseExpr("--path", str)
 				if err != nil {
-					return fmt.Errorf(`labels are of form "cue import -l foo -l 'strings.ToLower(bar)'": %v`, err)
+					return nil, fmt.Errorf(`labels are of form "cue import -l foo -l 'strings.ToLower(bar)'": %v`, err)
 				}
 
 				str, err := inst.Eval(l).String()
 				if err != nil {
-					return fmt.Errorf("unsupported label path type: %v", err)
+					return nil, fmt.Errorf("unsupported label path type: %v", err)
 				}
 				pathElems = append(pathElems, ast.NewString(str))
 			}
@@ -458,9 +466,9 @@ func combineExpressions(cmd *Command, pkg, filename string, idx int, objs ...ast
 			obj, ok := expr.(*ast.StructLit)
 			if !ok {
 				if _, ok := expr.(*ast.ListLit); ok {
-					return fmt.Errorf("expected struct as object root, did you mean to use the --list flag?")
+					return nil, fmt.Errorf("expected struct as object root, did you mean to use the --list flag?")
 				}
-				return fmt.Errorf("cannot map non-struct to object root")
+				return nil, fmt.Errorf("cannot map non-struct to object root")
 			}
 			f.Decls = append(f.Decls, obj.Elts...)
 		} else {
@@ -492,16 +500,7 @@ func combineExpressions(cmd *Command, pkg, filename string, idx int, objs ...ast
 		}
 	}
 
-	b, err := format.Node(f, format.Simplify())
-	if err != nil {
-		return fmt.Errorf("error formatting file: %v", err)
-	}
-
-	if cueFile == "-" {
-		_, err := cmd.OutOrStdout().Write(b)
-		return err
-	}
-	return ioutil.WriteFile(cueFile, b, 0644)
+	return f, nil
 }
 
 type listIndex struct {