repl: don’t complete non-simple expressions

Change the regular expression that recognizes “simple” JS expressions
to requiring that the full line needs to match it.

Previously, in terms like `a().b.`, `b.` would be a partial match.
This meant that completion would evaluate `b` and either fail with
a `ReferenceError` or, if `b` was some global, return the properties
of the global `b` object.

PR-URL: #6192
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

lib/repl.js

@@ -627,7 +627,7 @@ ArrayStream.prototype.write = function() {};
 
 const requireRE = /\brequire\s*\(['"](([\w\.\/-]+\/)?([\w\.\/-]*))/;
 const simpleExpressionRE =
-    /(([a-zA-Z_$](?:\w|\$)*)\.)*([a-zA-Z_$](?:\w|\$)*)\.?$/;
+    /^\s*(([a-zA-Z_$](?:\w|\$)*)\.)*([a-zA-Z_$](?:\w|\$)*)\.?$/;
 
 function intFilter(item) {
   // filters out anything not starting with A-Z, a-z, $ or _

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

@@ -251,3 +251,11 @@ testMe.complete('obj.', common.mustCall(function(error, data) {
   assert.strictEqual(data[0].indexOf('obj.1a'), -1);
   assert.notStrictEqual(data[0].indexOf('obj.a'), -1);
 }));
+
+// Don't try to complete results of non-simple expressions
+putIn.run(['.clear']);
+putIn.run(['function a() {}']);
+
+testMe.complete('a().b.', common.mustCall((error, data) => {
+  assert.deepEqual(data, [[], undefined]);
+}));