[clang-format] Fix breaking of qualified operator

[krasimir]

Summary

From https://bugs.llvm.org/show_bug.cgi?id=40516

$ cat a.cpp
const NamespaceName::VeryLongClassName &NamespaceName::VeryLongClassName::myFunction() {
  // do stuff
}

const NamespaceName::VeryLongClassName &NamespaceName::VeryLongClassName::operator++() {
  // do stuff
}
$ ~/ll/build/opt/bin/clang-format -style=LLVM a.cpp
const NamespaceName::VeryLongClassName &
NamespaceName::VeryLongClassName::myFunction() {
  // do stuff
}

const NamespaceName::VeryLongClassName &NamespaceName::VeryLongClassName::
operator++() {
  // do stuff
}

What was happening is that the split penalty before operator was being set to
a smaller value by a prior if block. Moved checks around to fix this and added a
regression test.

[krasimir]

• Format tests

[djasper]

Thank you.

lib/Format/TokenAnnotator.cpp

if (Right.is(tok::l_square)) {
     if (Right.is(TT_LambdaLSquare) && Left.is(tok::equal))
       return 35;
     if (!Right.isOneOf(TT_ObjCMethodExpr, TT_LambdaLSquare,
                        TT_ArrayInitializerLSquare,
                        TT_DesignatedInitializerLSquare, TT_AttributeSquare))
       return 500;
   }
 
+  if (Left.is(tok::coloncolon) ||
+      (Right.is(tok::period) && Style.Language == FormatStyle::LK_Proto))
+    return 500;
   if (Right.isOneOf(TT_StartOfName, TT_FunctionDeclarationName) ||
       Right.is(tok::kw_operator)) {
     if (Line.startsWith(tok::kw_for) && Right.PartOfMultiVariableDeclStmt)
       return 3;
     if (Left.is(TT_StartOfName))
       return 110;
     if (InFunctionDecl && Right.NestingLevel == 0)
       return Style.PenaltyReturnTypeOnItsOwnLine;
     return 200;
   }
   if (Right.is(TT_PointerOrReference))
     return 190;
   if (Right.is(TT_LambdaArrow))
     return 110;
   if (Left.is(tok::equal) && Right.is(tok::l_brace))
     return 160;
   if (Left.is(TT_CastRParen))
     return 100;
-  if (Left.is(tok::coloncolon) ||
-      (Right.is(tok::period) && Style.Language == FormatStyle::LK_Proto))
-    return 500;
   if (Left.isOneOf(tok::kw_class, tok::kw_struct))
     return 5000;
   if (Left.is(tok::comment))
     return 1000;
 
   if (Left.isOneOf(TT_RangeBasedForLoopColon, TT_InheritanceColon,
                    TT_CtorInitializerColon))
     return 2;

unittests/Format/FormatTest.cpp

TEST_F(FormatTest, BreaksFunctionDeclarations) {
   verifyFormat("void aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(\n"
                "    aaaaaaaaaaaaaaaaaaaaaaaaa* const aaaaaaaaaaaa) {}",
                Style);
   verifyFormat("void aaaaaaa(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa*\n"
                "                 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa) {}",
                Style);
 }
 
+TEST_F(FormatTest, DontBreakBeforeQualifiedOperator) {
+  // Regression test for https://bugs.llvm.org/show_bug.cgi?id=40516:
+  // Prefer keeping `::` followed by `operator` together.
+  EXPECT_EQ("const aaaa::bbbbbbb &\n"
+            "ccccccccc::operator++() {\n"
+            "  stuff();\n"
+            "}",
+            format("const aaaa::bbbbbbb\n"
+                   "&ccccccccc::operator++() { stuff(); }",
+                   getLLVMStyleWithColumns(40)));
+}
+
 TEST_F(FormatTest, TrailingReturnType) {
   verifyFormat("auto foo() -> int;\n");
   verifyFormat("struct S {\n"
                "  auto bar() const -> int;\n"
                "};");
   verifyFormat("template <size_t Order, typename T>\n"
                "auto load_img(const std::string &filename)\n"
                "    -> alias::tensor<Order, T, mem::tag::cpu> {}");