topdown/type: Fix inconsistent is_<type> return values.

Fixes open-policy-agent#4943

Signed-off-by: Philip Conrad <philipaconrad@gmail.com>

test/cases/testdata/typebuiltin/test-typebuiltin-0829.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_number
   query: data.generated.p = x
-  want_result: []
+  want_result:
+   - x: false

test/cases/testdata/typebuiltin/test-typebuiltin-0830.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_number
   query: data.generated.p = x
-  want_result: []
+  want_result:
+  - x: false

test/cases/testdata/typebuiltin/test-typebuiltin-0833.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_string
   query: data.generated.p = x
-  want_result: []
+  want_result:
+  - x: false

test/cases/testdata/typebuiltin/test-typebuiltin-0834.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_string
   query: data.generated.p = x
-  want_result: []
+  want_result:
+  - x: false

test/cases/testdata/typebuiltin/test-typebuiltin-0837.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_boolean
   query: data.generated.p = x
-  want_result: []
+  want_result:
+  - x: false

test/cases/testdata/typebuiltin/test-typebuiltin-0838.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_boolean
   query: data.generated.p = x
-  want_result: []
+  want_result:
+  - x: false

test/cases/testdata/typebuiltin/test-typebuiltin-0841.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_array
   query: data.generated.p = x
-  want_result: []
+  want_result:
+  - x: false

test/cases/testdata/typebuiltin/test-typebuiltin-0843.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_set
   query: data.generated.p = x
-  want_result: []
+  want_result:
+  - x: false

test/cases/testdata/typebuiltin/test-typebuiltin-0845.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_object
   query: data.generated.p = x
-  want_result: []
+  want_result:
+  - x: false

test/cases/testdata/typebuiltin/test-typebuiltin-0847.yaml

@@ -9,4 +9,5 @@ cases:
     }
   note: typebuiltin/is_null
   query: data.generated.p = x
-  want_result: []
+  want_result:
+  - x: false

topdown/type.go

@@ -1,4 +1,4 @@
-// Copyright 2018 The OPA Authors.  All rights reserved.
+// Copyright 2022 The OPA Authors.  All rights reserved.
 // Use of this source code is governed by an Apache2
 // license that can be found in the LICENSE file.
 
@@ -13,7 +13,7 @@ func builtinIsNumber(a ast.Value) (ast.Value, error) {
 	case ast.Number:
 		return ast.Boolean(true), nil
 	default:
-		return nil, BuiltinEmpty{}
+		return ast.Boolean(false), nil
 	}
 }
 
@@ -22,7 +22,7 @@ func builtinIsString(a ast.Value) (ast.Value, error) {
 	case ast.String:
 		return ast.Boolean(true), nil
 	default:
-		return nil, BuiltinEmpty{}
+		return ast.Boolean(false), nil
 	}
 }
 
@@ -31,7 +31,7 @@ func builtinIsBoolean(a ast.Value) (ast.Value, error) {
 	case ast.Boolean:
 		return ast.Boolean(true), nil
 	default:
-		return nil, BuiltinEmpty{}
+		return ast.Boolean(false), nil
 	}
 }
 
@@ -40,7 +40,7 @@ func builtinIsArray(a ast.Value) (ast.Value, error) {
 	case *ast.Array:
 		return ast.Boolean(true), nil
 	default:
-		return nil, BuiltinEmpty{}
+		return ast.Boolean(false), nil
 	}
 }
 
@@ -49,7 +49,7 @@ func builtinIsSet(a ast.Value) (ast.Value, error) {
 	case ast.Set:
 		return ast.Boolean(true), nil
 	default:
-		return nil, BuiltinEmpty{}
+		return ast.Boolean(false), nil
 	}
 }
 
@@ -58,7 +58,7 @@ func builtinIsObject(a ast.Value) (ast.Value, error) {
 	case ast.Object:
 		return ast.Boolean(true), nil
 	default:
-		return nil, BuiltinEmpty{}
+		return ast.Boolean(false), nil
 	}
 }
 
@@ -67,7 +67,7 @@ func builtinIsNull(a ast.Value) (ast.Value, error) {
 	case ast.Null:
 		return ast.Boolean(true), nil
 	default:
-		return nil, BuiltinEmpty{}
+		return ast.Boolean(false), nil
 	}
 }