[breaking] some magic variables e.g. __loop and __arg

will not be visible to calling features, which IMO is good, less variable clutter
decision is to keep __arg __loop __row and __num as [hidden] variables
they will continue to be [visible] to called features but thats about it
and of course be available to use in any js expression / assertion
this shold hoefully solve all problems discussed in #1436
callonce also looks good, we have one existing test [callonce-bg.feature]

karate-core/src/main/java/com/intuit/karate/core/ScenarioEngine.java

@@ -994,7 +994,7 @@ public void doc(String exp) {
     public void init() { // not in constructor because it has to be on Runnable.run() thread 
         JS = JsEngine.local();
         logger.trace("js context: {}", JS);
-        setVariables(runtime.magicVariables);
+        runtime.magicVariables.forEach((k, v) -> setHiddenVariable(k, v));
         attachVariables(); // re-hydrate any functions from caller or background
         setHiddenVariable(KARATE, bridge);
         setHiddenVariable(READ, readFunction);

karate-core/src/main/java/com/intuit/karate/core/ScenarioRuntime.java

@@ -251,6 +251,10 @@ private Map<String, Object> initMagicVariables() {
                 map.putAll(caller.arg.getValue());
             }
         } else {
+            // karate principle: parent variables are always "visible"
+            // so we inject the parent magic variables
+            // but they will be over-written by what is local to this scenario
+            map.putAll(caller.parentRuntime.magicVariables);
             map.put("__arg", caller.arg);
             map.put("__loop", caller.getLoopIndex());
             if (caller.arg != null && caller.arg.isMap()) {

karate-core/src/test/java/com/intuit/karate/core/FeatureRuntimeTest.java

@@ -207,6 +207,11 @@ void testToBean() {
     @Test
     void testOutlineBackground() {
         run("outline-background.feature");
-    }    
+    }  
+
+    @Test
+    void testCallArg() {
+        run("call-arg.feature");
+    }     
 
 }

karate-core/src/test/java/com/intuit/karate/core/PerfHookTest.java

@@ -60,7 +60,7 @@ void testPerfHook1() {
         assertEquals(featureResult.getScenarioCount(), 1);
         assertEquals(featureResult.getPassedCount(), 1);
         assertEquals(featureResult.getFailedCount(), 0);
-        matchContains(featureResult.getVariables(), "{ bar: '" + bar + "', configSource: 'normal', responseStatus: 200, response: { foo: ['" + bar + "'] } }");
+        matchContains(featureResult.getVariables(), "{ configSource: 'normal', responseStatus: 200, response: { foo: ['" + bar + "'] } }");
     }
 
     @Test
@@ -77,7 +77,7 @@ void testPerfHook2() {
         assertEquals(featureResult.getScenarioCount(), 1);
         assertEquals(featureResult.getPassedCount(), 0);
         assertEquals(featureResult.getFailedCount(), 1);
-        matchContains(featureResult.getVariables(), "{ bar: '" + bar + "', configSource: 'normal', responseStatus: 200, response: { foo: ['" + bar + "'] } }");
+        matchContains(featureResult.getVariables(), "{ configSource: 'normal', responseStatus: 200, response: { foo: ['" + bar + "'] } }");
     }
 
     @Test
@@ -94,7 +94,7 @@ void testPerfHook3() {
         assertEquals(featureResult.getScenarioCount(), 1);
         assertEquals(featureResult.getPassedCount(), 0);
         assertEquals(featureResult.getFailedCount(), 1);
-        matchContains(featureResult.getVariables(), "{ bar: '" + bar + "', configSource: 'normal', responseStatus: 200, response: { foo: ['" + bar + "'] } }");
+        matchContains(featureResult.getVariables(), "{ configSource: 'normal', responseStatus: 200, response: { foo: ['" + bar + "'] } }");
     }
 
     @Test

karate-core/src/test/java/com/intuit/karate/core/ScenarioRuntimeTest.java

@@ -140,23 +140,23 @@ void testCallKarateFeature() {
                 "def b = 'bar'",
                 "def res = call read('called1.feature')"
         );
-        matchVar("res", "{ a: 1, b: 'bar', foo: { hello: 'world' }, configSource: 'normal', __arg: null, __loop: -1 }");
+        matchVar("res", "{ a: 1, b: 'bar', foo: { hello: 'world' }, configSource: 'normal' }");
         run(
                 "def b = 'bar'",
                 "def res = call read('called1.feature') { foo: 'bar' }"
         );
-        matchVar("res", "{ a: 1, b: 'bar', foo: { hello: 'world' }, configSource: 'normal', __arg: { foo: 'bar' }, __loop: -1 }");
+        matchVar("res", "{ a: 1, b: 'bar', foo: { hello: 'world' }, configSource: 'normal' }");
         run(
                 "def b = 'bar'",
                 "def res = call read('called1.feature') [{ foo: 'bar' }]"
         );
-        matchVar("res", "[{ a: 1, b: 'bar', foo: { hello: 'world' }, configSource: 'normal', __arg: { foo: 'bar' }, __loop: 0 }]");
+        matchVar("res", "[{ a: 1, b: 'bar', foo: { hello: 'world' }, configSource: 'normal' }]");
         run(
                 "def b = 'bar'",
                 "def fun = function(i){ if (i == 1) return null; return { index: i } }",
                 "def res = call read('called1.feature') fun"
         );
-        matchVar("res", "[{ a: 1, b: 'bar', foo: { hello: 'world' }, configSource: 'normal', __arg: { index: 0 }, __loop: 0, index: 0, fun: '#ignore' }]");
+        matchVar("res", "[{ a: 1, b: 'bar', foo: { hello: 'world' }, configSource: 'normal', fun: '#ignore' }]");
     }
 
     @Test
@@ -215,7 +215,7 @@ void testCallFromJs() {
         run(
                 "def res = karate.call('called1.feature')"
         );
-        matchVar("res", "{ a: 1, foo: { hello: 'world' }, configSource: 'normal', __arg: null, __loop: -1 }");
+        matchVar("res", "{ a: 1, foo: { hello: 'world' }, configSource: 'normal' }");
     }
 
     @Test

karate-core/src/test/java/com/intuit/karate/core/call-arg-called.feature

@@ -0,0 +1,9 @@
+Feature:
+
+Background:
+* match __arg == { foo: 'bar' }
+* call read('call-arg-common.feature')
+
+Scenario:
+* print 'in scenario'
+* match __arg == { foo: 'bar' }

karate-core/src/test/java/com/intuit/karate/core/call-arg-common.feature

@@ -0,0 +1,4 @@
+Feature:
+
+Scenario:
+* def hello = function(){ return 'hello' }

karate-core/src/test/java/com/intuit/karate/core/call-arg.feature

@@ -0,0 +1,8 @@
+Feature:
+
+Background:
+* print 'in background'
+
+Scenario:
+* def params = { 'foo': 'bar' }
+* call read('call-arg-called.feature') params

karate-demo/src/test/java/demo/calltable/call-table.feature

@@ -17,10 +17,6 @@ Background:
 # use json-path to 'un-pack' the array of kittens created
 * def created = $result[*].response
 
-# for each iteration, a variable called '__loop' is set for convenience
-# which can be accessed in the called feature as well
-* match result[*].__loop == [0, 1, 2, 3, 4, 5]
-
 # which is not even needed for most data-driven assertions
 * match created[*].name == $kittens[*].name