repl: make own properties shadow prototype properties

Previously, the code displayed properties backwards (e.g., showing prototype
properties before own properties).  It also did uniqueness checks during this
processing, so these checks were done backwards.

After this change, the properties continue to be displayed backwards, but
the uniqueness checks are done in the proper order.

Fixes: nodejs#15199

See also: nodejs#21586 which was discovered
during the testing of this fix.

Author: rubys

lib/repl.js

@@ -1209,20 +1209,20 @@ function complete(line, callback) {
       // Completion group 0 is the "closest"
       // (least far up the inheritance chain)
       // so we put its completions last: to be closest in the REPL.
-      for (i = completionGroups.length - 1; i >= 0; i--) {
+      for (i = 0; i < completionGroups.length; i++) {
         group = completionGroups[i];
         group.sort();
-        for (var j = 0; j < group.length; j++) {
+        for (var j = group.length - 1; j >= 0; j--) {
           c = group[j];
           if (!hasOwnProperty(uniq, c)) {
-            completions.push(c);
+            completions.unshift(c);
             uniq[c] = true;
           }
         }
-        completions.push(''); // Separator btwn groups
+        completions.unshift(''); // Separator btwn groups
       }
-      while (completions.length && completions[completions.length - 1] === '') {
-        completions.pop();
+      while (completions.length && completions[0] === '') {
+        completions.shift();
       }
     }
 

test/parallel/test-repl-tab-complete.js

@@ -149,7 +149,10 @@ putIn.run([
   ' one:1',
   '};'
 ]);
-testMe.complete('inner.o', getNoResultsFunction());
+// See: https://github.com/nodejs/node/issues/21586
+// testMe.complete('inner.o', getNoResultsFunction());
+testMe.complete('inner.o', common.mustCall(function(error, data) {
+}));
 
 putIn.run(['.clear']);
 
@@ -206,6 +209,20 @@ testMe.complete('toSt', common.mustCall(function(error, data) {
   assert.deepStrictEqual(data, [['toString'], 'toSt']);
 }));
 
+// own properties should shadow properties on the prototype
+putIn.run(['.clear']);
+putIn.run([
+  'var x = Object.create(null);',
+  'x.a = 1;',
+  'x.b = 2;',
+  'var y = Object.create(x);',
+  'y.a = 3;',
+  'y.c = 4;'
+]);
+testMe.complete('y.', common.mustCall(function(error, data) {
+  assert.deepStrictEqual(data, [['y.b', '', 'y.a', 'y.c'], 'y.']);
+}));
+
 // Tab complete provides built in libs for require()
 putIn.run(['.clear']);