[clang-format] structured binding in range for detected as Objective C

[MyDeveloperDay]

Summary

Sometime after 6.0.0 and the current trunk 9.0.0 the following code would be considered as objective C and not C++

Reported by: https://twitter.com/mattgodbolt/status/1096188576503644160

$ clang-format.exe test.h
Configuration file(s) do(es) not support Objective-C: C:\clang\build\.clang-format

• test.h --

#include <vector>
#include <string>

std::vector<std::pair<std::string,std::string>> C;

void foo()
{
   for (auto && [A,B] : C)
   {
       std::string D = A + B;
   }
}

The following code fixes this issue of incorrect detection

[klimek]

lg

lib/Format/TokenAnnotator.cpp

bool StartsObjCMethodExpr =
         Left->isNot(TT_LambdaLSquare) &&
         !CurrentToken->isOneOf(tok::l_brace, tok::r_square) &&
         (!Parent ||
          Parent->isOneOf(tok::colon, tok::l_square, tok::l_paren,
                          tok::kw_return, tok::kw_throw) ||
          Parent->isUnaryOperator() ||
          // FIXME(bug 36976): ObjC return types shouldn't use TT_CastRParen.
          Parent->isOneOf(TT_ObjCForIn, TT_CastRParen) ||
-         getBinOpPrecedence(Parent->Tok.getKind(), true, true) > prec::Unknown);
+         // for (auto && [A,B] : C)  && structure binding seen as ObjCMethodExpr
+         (Parent->isNot(tok::ampamp) &&
+          getBinOpPrecedence(Parent->Tok.getKind(), true, true) >
+              prec::Unknown));
     bool ColonFound = false;
 
     unsigned BindingIncrease = 1;
     if (Left->isCppStructuredBinding(Style)) {
       Left->Type = TT_StructuredBindingLSquare;
     } else if (Left->is(TT_Unknown)) {
       if (StartsObjCMethodExpr) {
         Left->Type = TT_ObjCMethodExpr;

unittests/Format/FormatTest.cpp

TEST_F(FormatTest, GuessLanguageWithCpp11AttributeSpecifiers) {
   EXPECT_EQ(FormatStyle::LK_Cpp,
             guessLanguage("foo.h", "[[using clang: fallthrough]];"));
   EXPECT_EQ(FormatStyle::LK_ObjC,
             guessLanguage("foo.h", "[[abusing clang:fallthrough] bar];"));
   EXPECT_EQ(FormatStyle::LK_Cpp,
             guessLanguage("foo.h", "[[using gsl: suppress(\"type\")]];"));
   EXPECT_EQ(
       FormatStyle::LK_Cpp,
+      guessLanguage("foo.h", "for (auto &&[endpoint, stream] : streams_)"));
+  EXPECT_EQ(
+      FormatStyle::LK_Cpp,
       guessLanguage("foo.h",
                     "[[clang::callable_when(\"unconsumed\", \"unknown\")]]"));
   EXPECT_EQ(FormatStyle::LK_Cpp, guessLanguage("foo.h", "[[foo::bar, ...]]"));
 }
 
 TEST_F(FormatTest, GuessLanguageWithCaret) {
   EXPECT_EQ(FormatStyle::LK_Cpp, guessLanguage("foo.h", "FOO(^);"));
   EXPECT_EQ(FormatStyle::LK_Cpp, guessLanguage("foo.h", "FOO(^, Bar);"));