encoding/openapi: make title and version defaults

The title and version may cause a conflict when merging two
OpenAPI schema. Make them default values to allow merging
OpenAPI shema in such a case.

This is orthogonal to an option to omit certain sections.

Change-Id: If65beee3cb9c5da835c77f9c1bd448b68f97e62c
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/5744
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>

cmd/cue/cmd/testdata/script/def_openapi.txt

@@ -1,3 +1,5 @@
+cue def openapi+cue: expect-cue-out -o -
+
 cue def foo.cue -o openapi:-
 cmp stdout expect-json-out
 
@@ -172,8 +174,8 @@ components: schemas: {
 package foo
 
 info: {
-	title:   "My OpenAPI"
-	version: "v1alpha1"
+	title:   *"My OpenAPI" | string
+	version: *"v1alpha1" | string
 }
 
 Bar :: {
@@ -187,8 +189,8 @@ Foo :: {
 }
 -- expect-cue2 --
 info: {
-	title:   "Some clever title."
-	version: "v1"
+	title:   *"Some clever title." | string
+	version: *"v1" | string
 }
 Bar :: {
 	foo: Foo

cmd/cue/cmd/testdata/script/import_auto.txt

@@ -5,8 +5,8 @@ cmp stdout expect-openapi
 // An OpenAPI file
 
 info: {
-	title:   "An OpenAPI file"
-	version: "v1beta1"
+	title:   *"An OpenAPI file" | string
+	version: *"v1beta1" | string
 }
 
 Foo :: {

encoding/openapi/decode.go

@@ -61,7 +61,7 @@ func Extract(data *cue.Instance, c *Config) (*ast.File, error) {
 		p := &ast.Package{Name: ast.NewIdent(c.PkgName)}
 		p.AddComment(cg)
 		add(p)
-	} else if cg != nil {
+	} else {
 		add(cg)
 	}
 
@@ -86,10 +86,30 @@ func Extract(data *cue.Instance, c *Config) (*ast.File, error) {
 	// }
 
 	if info := v.Lookup("info"); info.Exists() {
-		add(&ast.Field{
-			Label: ast.NewIdent("info"),
-			Value: info.Syntax().(ast.Expr),
-		})
+		decls := []interface{}{}
+		if st, ok := info.Syntax().(*ast.StructLit); ok {
+			// Remove title.
+			for _, d := range st.Elts {
+				if f, ok := d.(*ast.Field); ok {
+					switch name, _, _ := ast.LabelName(f.Label); name {
+					case "title", "version":
+						// title: *"title" | string
+						decls = append(decls, &ast.Field{
+							Label: f.Label,
+							Value: ast.NewBinExpr(token.OR,
+								&ast.UnaryExpr{Op: token.MUL, X: f.Value},
+								ast.NewIdent("string")),
+						})
+						continue
+					}
+				}
+				decls = append(decls, d)
+			}
+			add(&ast.Field{
+				Label: ast.NewIdent("info"),
+				Value: ast.NewStruct(decls...),
+			})
+		}
 	}
 
 	if i < len(js.Decls) {

encoding/openapi/testdata/openapi.cue

@@ -1,4 +1,3 @@
-
 // An OpenAPI testing package.
 package openapi
 

encoding/openapi/testdata/script/basics.txtar

@@ -28,8 +28,8 @@ components:
 package foo
 
 info: {
-	title:   "Users schema"
-	version: "v1beta1"
+	title:   *"Users schema" | string
+	version: *"v1beta1" | string
 	contact: {
 		name: "The CUE Authors"
 		url:  "https://cuelang.org"