Fix null types generation

Author: spinillos

generate_test.go

@@ -48,7 +48,6 @@ func TestGenerateWithImports(t *testing.T) {
 			"imports/struct_shorthand": "Shorthand struct notation is currently unsupported, needs fixing",
 			"imports/single_embed":     "Single-item struct embeds should be treated as just another interface to compose, but get confused with references - #60",
 			"imports/inline_comments":  "Inline comments do not appear be retrievable from cue.Value.Doc()",
-			"imports/nulltype":         "null types are not handled correctly",
 		},
 	}
 

generator.go

@@ -1226,7 +1226,13 @@ func (g generator) tsprintField(v cue.Value, isType bool) (ts.Expr, error) {
 			return nil, valError(v, "bounds constraints are not supported as they lack a direct typescript equivalent")
 		}
 		fallthrough
-	case cue.FloatKind, cue.IntKind, cue.BoolKind, cue.NullKind, cue.StructKind:
+	case cue.NullKind:
+		// It evaluates single null value
+		if op == cue.NoOp && len(dvals) == 0 {
+			return tsprintType(cue.NullKind), nil
+		}
+		fallthrough
+	case cue.FloatKind, cue.IntKind, cue.BoolKind, cue.StructKind:
 		// Having eliminated the possibility of bounds/constraints, we're left
 		// with disjunctions and basic types.
 		switch op {
@@ -1292,6 +1298,8 @@ func tsprintType(k cue.Kind) ts.Expr {
 		return ts.Ident("number")
 	case cue.TopKind:
 		return ts.Ident("unknown")
+	case cue.NullKind:
+		return ts.Ident("null")
 	default:
 		return nil
 	}

testdata/imports/nulltype.txtar

@@ -15,12 +15,12 @@ obj: {
 
 export type nullType = null;
 
-export type nullInUnion = string | null;
+export type nullInUnion = (string | null);
 
-export type nullDefault = "foo" | "bar" | null;
+export type nullDefault = ('foo' | 'bar' | null);
 
 export const defaultnullDefault: nullDefault = null;
 
 export interface obj {
-    nullField: null
-}
+  nullField: null;
+}