Add property support for pointers to bools and strings

The only append semantics for bool that result in a no-op when the zero
value is appended is to OR the two values together, but that is rarely
the desired semantics.  Add support for *bool and *string as property
types, where appending a nil pointer is a no-op.  For *bool, appending a
non-nil pointer replaces the destination with the value.  For *string,
appending a non-nil pointer appends the value.

This also provides a more reliable replacement for
ModuleContext.ContainsProperty, as the  build logic can tell that the
property was set, even if it was set by a  mutator and not by the
blueprints file, by testing against nil.

[]string already provides these semantics for lists.

Setting a *bool or *string property from a blueprints file is the same
syntax as setting a bool or a string property.

1 files changed, 36 insertions, 0 deletions

diff --git a/unpack_test.go b/unpack_test.go
index 0b31efc..77a57ec 100644
--- a/unpack_test.go
+++ b/unpack_test.go
@@ -33,6 +33,24 @@ var validUnpackTestCases = []struct {
 	{`
 		m {
 			name: "abc",
+			blank: "",
+		}
+		`,
+		struct {
+			Name  *string
+			Blank *string
+			Unset *string
+		}{
+			Name:  proptools.StringPtr("abc"),
+			Blank: proptools.StringPtr(""),
+			Unset: nil,
+		},
+		nil,
+	},
+
+	{`
+		m {
+			name: "abc",
 		}
 		`,
 		struct {
@@ -58,6 +76,24 @@ var validUnpackTestCases = []struct {
 
 	{`
 		m {
+			isGood: true,
+			isBad: false,
+		}
+		`,
+		struct {
+			IsGood *bool
+			IsBad  *bool
+			IsUgly *bool
+		}{
+			IsGood: proptools.BoolPtr(true),
+			IsBad:  proptools.BoolPtr(false),
+			IsUgly: nil,
+		},
+		nil,
+	},
+
+	{`
+		m {
 			stuff: ["asdf", "jkl;", "qwert",
 				"uiop", "bnm,"],
 			empty: []