Index: clang/lib/Format/WhitespaceManager.cpp
===================================================================
--- clang/lib/Format/WhitespaceManager.cpp
+++ clang/lib/Format/WhitespaceManager.cpp
@@ -17,8 +17,8 @@
 namespace clang {
 namespace format {
 
-bool WhitespaceManager::Change::IsBeforeInFile::
-operator()(const Change &C1, const Change &C2) const {
+bool WhitespaceManager::Change::IsBeforeInFile::operator()(
+    const Change &C1, const Change &C2) const {
   return SourceMgr.isBeforeInTranslationUnit(
       C1.OriginalWhitespaceRange.getBegin(),
       C2.OriginalWhitespaceRange.getBegin());
@@ -465,6 +465,19 @@
         // definitions.
         return C.Tok->is(TT_StartOfName) ||
                C.Tok->is(TT_FunctionDeclarationName) ||
+               C.Tok->startsSequence(
+                   tok::l_paren, tok::l_paren, tok::identifier, tok::coloncolon,
+                   tok::identifier, tok::r_paren, tok::r_paren) ||
+               C.Tok->startsSequence(tok::l_square, tok::l_square,
+                                     tok::identifier, tok::coloncolon,
+                                     tok::identifier, tok::r_square,
+                                     tok::r_square) ||
+               C.Tok->startsSequence(tok::l_square, tok::l_square,
+                                     tok::identifier, tok::r_square,
+                                     tok::r_square) ||
+               C.Tok->startsSequence(tok::l_paren, tok::l_paren,
+                                     tok::identifier, tok::r_paren,
+                                     tok::r_paren) ||
                C.Tok->is(tok::kw_operator);
       },
       Changes, /*StartAt=*/0);
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -10135,6 +10135,47 @@
                "  unsigned c;\n"
                "}",
                Alignment);
+
+  // See llvm.org/PR40418
+  verifyFormat(
+      "void f(int              extremlylongparameternamexxxxxxxx1,\n"
+      "       long             extremlylongparameternamexxxxxxxx2,\n"
+      "       int              [[a::b]] extremlylongparameternamexxxxxxxx3,\n"
+      "       int __attribute__((a::b)) extremlylongparameternamexxxxxxxx4) "
+      "{}\n",
+      Alignment);
+
+  verifyFormat("void f(int              extremlylongparameternamexxxxxxxx1,\n"
+               "       long             extremlylongparameternamexxxxxxxx2,\n"
+               "       int              [[deprecated]] "
+               "extremlylongparameternamexxxxxxxx3,\n"
+               "       int __attribute__((deprecated)) "
+               "extremlylongparameternamexxxxxxxx4) "
+               "{}\n",
+               Alignment);
+
+  verifyFormat("int              a;\n"
+               "unsigned long    b;\n"
+               "int __attribute__((a::b)) d;\n"
+               "int              [[a::b]] c;\n"
+               "int __attribute__((a::b)) e;\n"
+               "int __attribute__((depreciated)) f;\n"
+               "int __attribute__((aligned(16))) g;\n",
+               Alignment);
+
+  verifyFormat("int              a;\n"
+               "unsigned long    b;\n"
+               "int __attribute__((a::b)) d;\n"
+               "int              [[deprecated]] c;\n"
+               "int __attribute__((a::b)) e;\n",
+               Alignment);
+
+  verifyFormat("int              a;\n"
+               "unsigned long    b;\n"
+               "int __attribute__((deprecated)) de;\n"
+               "int              [[deprecated]] c;\n"
+               "int __attribute__((a::b)) e;\n",
+               Alignment);
 }
 
 TEST_F(FormatTest, LinuxBraceBreaking) {