PY-27178 Parenthesised expression parsing doesn't hang at the end of file

Normally, it shouldn't happen, since Python lexer is supposed to put the
special STATEMENT_BREAK token right at the end of file, but apparently
it may not be the case during editing of an injected fragment.

python/src/com/jetbrains/python/parsing/ExpressionParsing.java

@@ -305,7 +305,8 @@ public class ExpressionParsing extends Parsing {
       else {
         final PsiBuilder.Marker err = myBuilder.mark();
         boolean empty = true;
-        while (myBuilder.getTokenType() != PyTokenTypes.RPAR &&
+        while (!myBuilder.eof() &&
+               myBuilder.getTokenType() != PyTokenTypes.RPAR &&
                myBuilder.getTokenType() != PyTokenTypes.LINE_BREAK &&
                myBuilder.getTokenType() != PyTokenTypes.STATEMENT_BREAK) {
           myBuilder.advanceLexer();

python/testData/editing/incompleteFunctionTypeComment.after.py

@@ -0,0 +1,2 @@
+def foo(bar):
+    # type: (foo.

python/testData/editing/incompleteFunctionTypeComment.py

@@ -0,0 +1,2 @@
+def foo(bar):
+    # type: (foo<caret>

python/testSrc/com/jetbrains/python/PyEditingTest.java

@@ -591,4 +591,9 @@ public class PyEditingTest extends PyTestCase {
                 "    return bar, 'so' \\\n" +
                 "                'me'");
   }
+
+  // PY-27178
+  public void testIncompleteFunctionTypeComment() {
+    doTypingTest('.');
+  }
 }