From 1fb436efa8cd7fb3f247e9b65132c416b8f91162 Mon Sep 17 00:00:00 2001
From: Pagan Gazzard <pjgazzard@googlemail.com>
Date: Fri, 10 Jun 2016 21:41:57 -0700
Subject: [PATCH] Added support for optionally matching keys of an object

---
 CHANGELOG.md                  |  1 +
 lib/ometajs/core.js           | 19 +++++++++++++++----
 src/bs-ometa-compiler.ometajs |  7 ++++++-
 test/files/simple.ometajs     |  4 ++++
 test/unit/api-test.js         |  3 ++-
 5 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 76d71488..2ed69bd2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,4 @@
+* Added support for optionally matching keys of an object, eg `@{ foo?: true }`
 * Added support for matching some keys of an object against corresponding rules,
 	eg `%{ foo: FooRule }`
 * Added support for matching all keys of an object against corresponding rules,
diff --git a/lib/ometajs/core.js b/lib/ometajs/core.js
index 22311594..41b2e0bc 100644
--- a/lib/ometajs/core.js
+++ b/lib/ometajs/core.js
@@ -694,12 +694,23 @@
 			var ruleKeys = Object.keys(x),
 				result = {};
 			if(matchAllInput) {
-				this._pred(ruleKeys.length === Object.keys(v).length);
+				var inputLength = Object.keys(v).length;
+				this._pred(ruleKeys.length >= inputLength);
 			}
 			for(var i = 0; i < ruleKeys.length; i++) {
-				var key = ruleKeys[i];
-				this._pred(v.hasOwnProperty(key));
-				result[key] = this._applyWithArgs('applyFn', x[key], v[key]);
+				var key = ruleKeys[i],
+					exists = v.hasOwnProperty(key),
+					ruleFn = x[key][0],
+					required = x[key][1];
+				if(required) {
+					this._pred(exists);
+				} else if(!exists) {
+					continue;
+				}
+				result[key] = this._applyWithArgs('applyFn', ruleFn, v[key]);
+			}
+			if(matchAllInput) {
+				this._pred(Object.keys(result).length === inputLength);
 			}
 			return v;
 		},
diff --git a/src/bs-ometa-compiler.ometajs b/src/bs-ometa-compiler.ometajs
index 1fad8413..787efc64 100644
--- a/src/bs-ometa-compiler.ometajs
+++ b/src/bs-ometa-compiler.ometajs
@@ -64,7 +64,10 @@ export ometa BSOMetaParser {
   objectRules    = {{}}:o
                    (objectRule:x ',' -> x)*:a
                    objectRule:x                                        -> a.concat([x]),
-  objectRule     = BSJSParser.jsonPropName:n ":" expr:x                -> [n, x],
+  objectRule     = BSJSParser.jsonPropName:n
+                   ( "?" -> false
+                   |     -> true
+                   ):required ":" expr:x                               -> [n, x, required],
   param          = ":" name:n                                          -> n,
   ruleName       = name
                  | spaces tsString,
@@ -109,6 +112,8 @@ export ometa BSOMetaTranslator {
   Lookahead  transFn:x                     -> ['this._lookahead(',     x, ')']                                     .join(''),
   Object     [ ( [ string:key
                    transFn:x
+                   (true|false):required
+                   {['[', x, ',', required, ']'].join('')}:x
                  ]
                  -> [JSON.stringify(key), x].join(':')
                )+:o
diff --git a/test/files/simple.ometajs b/test/files/simple.ometajs
index e75b7a37..8cbff1e5 100644
--- a/test/files/simple.ometajs
+++ b/test/files/simple.ometajs
@@ -35,4 +35,8 @@ export ometa Simple {
 			%{ 'simple': true, 'simpler': true }
 			-> 'should fail'
 		|	-> 'ok'
+	,
+	ObjectRulesMatchOptional =
+		@{ 'simple': true, 'simpler'?: true }
+		-> 'ok'
 }
diff --git a/test/unit/api-test.js b/test/unit/api-test.js
index 6bf6a2c1..fa7b69b5 100644
--- a/test/unit/api-test.js
+++ b/test/unit/api-test.js
@@ -25,7 +25,8 @@ var testMatches = {
 	ObjectRulesMatchAll1: { 'simple': true },
 	ObjectRulesMatchAll2: { 'simple': true, 'simpler': true },
 	ObjectRulesMatchPartial1: { 'simple': true, 'simpler': true },
-	ObjectRulesMatchPartial2: { 'simple': true }
+	ObjectRulesMatchPartial2: { 'simple': true },
+	ObjectRulesMatchOptional: { 'simple': true }
 };
 
 var runTests = function(test, grammar) {