clang-format: [Java] format Java lambda expressions

[het]

Summary

Support Java lambda expressions

[het]

Will this work for now? The way the fake paren parsing works, we will have (using '[' ']' as fake parens):

[[([a, b]) -> a] + b]

When we really want:

[([a, b]) -> [a + b]]

[djasper]

I think we should directly try to get this right with the fake parentheses. I'll prepare a patch. Feel free to just abandon this patch.

lib/Format/TokenAnnotator.cpp

bool TokenAnnotator::spaceRequiredBefore(const AnnotatedLine &Line,
   if (Left.Type == TT_UnaryOperator)
     return Right.Type == TT_BinaryOperator;
   if (Left.Type == TT_CastRParen)
     return Style.SpaceAfterCStyleCast || Right.Type == TT_BinaryOperator;
   if (Left.is(tok::greater) && Right.is(tok::greater)) {
     return Right.Type == TT_TemplateCloser && Left.Type == TT_TemplateCloser &&
            (Style.Standard != FormatStyle::LS_Cpp11 || Style.SpacesInAngles);
   }
+  if (Style.Language == FormatStyle::LK_Java &&
+      (Right.is(tok::arrow) || Left.is(tok::arrow)))
+    return true;
   if (Right.isOneOf(tok::arrow, tok::period, tok::arrowstar, tok::periodstar) ||
       Left.isOneOf(tok::arrow, tok::period, tok::arrowstar, tok::periodstar))
     return false;
   if (!Style.SpaceBeforeAssignmentOperators &&
       Right.getPrecedence() == prec::Assignment)
     return false;
   if (Right.is(tok::coloncolon) && Left.isNot(tok::l_brace))
     return (Left.Type == TT_TemplateOpener &&

unittests/Format/FormatTestJava.cpp

verifyFormat("return (result == null)\n"
                "    : bbbbbbbbbbbbbbbbb;",
                getStyleWithColumns(40));
   verifyFormat("return aaaaaaaaaaaaaaaaaaa()\n"
                "    .bbbbbbbbbbbbbbbbbbb()\n"
                "    .ccccccccccccccccccc();",
                getStyleWithColumns(40));
 }
 
+TEST_F(FormatTestJava, Lambdas) {
+  verifyFormat("Consumer<Integer> myConsumer = (y) -> {\n"
+               "  System.out.println(\"x = \" + x); // Statement A\n"
+               "  System.out.println(\"y = \" + y);\n"
+               "};");
+  verifyFormat("String s = invoke(() -> \"done\");");
+  verifyFormat("IntegerMath addition = (a, b) -> a + b");
+  verifyFormat("roster.stream()\n"
+               "    .filter(p -> p.getGender() == Person.Sex.MALE && p.getAge() >= 18 && p.getAge() <= 25)\n"
+               "    .map(p -> p.getEmailAddress())\n"
+               "    .forEach(email -> System.out.println(email));");
+  verifyFormat("roster.stream()\n"
+               "    .filter(p -> {\n"
+               "      System.out.println(\"foo\");\n"
+               "      return true;\n"
+               "    })\n"
+               "    .map(p -> p.getEmailAddress())\n"
+               "    .forEach(email -> System.out.println(email));");
+}
+
 } // end namespace tooling
 } // end namespace clang