json: allow "//" keys to be used as comments in bodies

Since the native syntax requires that attribute names and block types
be identifiers, there is no way for "//" to be a valid symbol in a body.
Therefore we can special-case it here as an ignored property name that
users can then use for comments.

This special handling intentionally does not apply to objects representing
zcl object expressions, since it _is_ valid to have non-identifier keys
there and so "//" may be a legitimate object key for some applications.

zcl/json/structure.go

@@ -52,6 +52,12 @@ func (b *body) Content(schema *zcl.BodySchema) (*zcl.BodyContent, zcl.Diagnostic
 	}
 
 	for k, attr := range b.obj.Attrs {
+		if k == "//" {
+			// Ignore "//" keys in objects representing bodies, to allow
+			// their use as comments.
+			continue
+		}
+
 		if _, ok := hiddenAttrs[k]; !ok {
 			var fixItHint string
 			suggestion := nameSuggestion(k, nameSuggestions)
@@ -140,6 +146,12 @@ func (b *body) PartialContent(schema *zcl.BodySchema) (*zcl.BodyContent, zcl.Bod
 func (b *body) JustAttributes() (zcl.Attributes, zcl.Diagnostics) {
 	attrs := make(map[string]*zcl.Attribute)
 	for name, jsonAttr := range b.obj.Attrs {
+		if name == "//" {
+			// Ignore "//" keys in objects representing bodies, to allow
+			// their use as comments.
+			continue
+		}
+
 		if _, hidden := b.hiddenAttrs[name]; hidden {
 			continue
 		}

zcl/json/structure_test.go

@@ -29,6 +29,19 @@ func TestBodyPartialContent(t *testing.T) {
 			},
 			0,
 		},
+		{
+			`{"//": "comment that should be ignored"}`,
+			&zcl.BodySchema{},
+			&zcl.BodyContent{
+				Attributes: map[string]*zcl.Attribute{},
+				MissingItemRange: zcl.Range{
+					Filename: "test.json",
+					Start:    zcl.Pos{Line: 1, Column: 40, Byte: 39},
+					End:      zcl.Pos{Line: 1, Column: 41, Byte: 40},
+				},
+			},
+			0,
+		},
 		{
 			`{"name":"Ermintrude"}`,
 			&zcl.BodySchema{
@@ -618,6 +631,11 @@ func TestBodyContent(t *testing.T) {
 			&zcl.BodySchema{},
 			1,
 		},
+		{
+			`{"//": "comment that should be ignored"}`,
+			&zcl.BodySchema{},
+			0,
+		},
 		{
 			`{"unknow": true}`,
 			&zcl.BodySchema{
@@ -698,6 +716,10 @@ func TestJustAttributes(t *testing.T) {
 				},
 			},
 		},
+		{
+			`{"//": "comment that should be ignored"}`,
+			map[string]*zcl.Attribute{},
+		},
 	}
 
 	for i, test := range tests {