loader: Insert root schema with key 'schema'

Previously if there was only one schema it was inserted into the
schema set with key 'input'. There was no good reason for this and
'schema' will do. This allows for us to have tighter validation of
schema references.

Signed-off-by: Torin Sandall <torinsandall@gmail.com>

ast/parser.go

@@ -1616,6 +1616,9 @@ func (b *metadataParser) Parse() (*Annotations, error) {
 
 var errInvalidSchemaRef = fmt.Errorf("invalid schema reference")
 
+// NOTE(tsandall): 'schema' is not registered as a root because it's not
+// supported by the compiler or evaluator today. Once we fix that, we can remove
+// this function.
 func parseSchemaRef(s string) (Ref, error) {
 
 	term, err := ParseTerm(s)

loader/loader.go

@@ -282,7 +282,7 @@ func loadSchemas(schemaPath string) (*ast.SchemaSet, error) {
 		if err != nil {
 			return nil, err
 		}
-		ss.Put(ast.InputRootRef, schema)
+		ss.Put(ast.SchemaRootRef, schema)
 		return ss, nil
 
 	}

loader/loader_test.go

@@ -765,7 +765,7 @@ func TestSchemas(t *testing.T) {
 				"foo/bar/baz.json": `{"type": "string"}`,
 			},
 			exp: map[string]string{
-				"input": `{"type": "string"}`,
+				"schema": `{"type": "string"}`,
 			},
 		},
 		{
@@ -802,7 +802,12 @@ func TestSchemas(t *testing.T) {
 						t.Fatal("unexpected error:", err)
 					}
 					for k, v := range tc.exp {
-						key := ast.MustParseRef(k)
+						var key ast.Ref
+						if k == "schema" {
+							key = ast.SchemaRootRef.Copy()
+						} else {
+							key = ast.MustParseRef(k)
+						}
 						var schema interface{}
 						util.Unmarshal([]byte(v), &schema)
 						result := ss.Get(key)