[clang-format] Don't wrap struct return types as structs

[rymiel]

Summary

When using BraceWrapping.AfterClass or BraceWrapping.AfterStruct, the
token annotator relies on the first token of the line to determine if
we're dealing with a struct or class, however, this check is faulty if
it's actually a function with an elaborated struct/class return type, as
is common in C.

This patch skips the check if the brace is already annotated as
FunctionLBrace, in which case we already know it's a function and should
be treated as such.

Fixes https://github.com/llvm/llvm-project/issues/58527

clang/lib/Format/TokenAnnotator.cpp

if (isAllmanBrace(Left) || isAllmanBrace(Right)) {
     // Ensure BraceWrapping for `public interface A {`.
     if (Style.BraceWrapping.AfterClass &&
         ((AccessSpecifier && FirstNonComment->Next &&
           FirstNonComment->Next->is(Keywords.kw_interface)) ||
          Line.startsWith(Keywords.kw_interface))) {
       return true;
     }
 
-    return (Line.startsWith(tok::kw_class) && Style.BraceWrapping.AfterClass) ||
-           (Line.startsWith(tok::kw_struct) && Style.BraceWrapping.AfterStruct);
+    // Don't attempt to interpret struct return types as structs.
+    if (Right.isNot(TT_FunctionLBrace)) {
+      return (Line.startsWith(tok::kw_class) &&
+              Style.BraceWrapping.AfterClass) ||
+             (Line.startsWith(tok::kw_struct) &&
+              Style.BraceWrapping.AfterStruct);
+    }
   }
 
   if (Left.is(TT_ObjCBlockLBrace) &&
       Style.AllowShortBlocksOnASingleLine == FormatStyle::SBS_Never) {
     return true;
   }
 
   // Ensure wrapping after __attribute__((XX)) and @interface etc.

clang/unittests/Format/FormatTest.cpp

EXPECT_EQ("try {\n"
             "  foo();\n"
             "}\n"
             "catch (...) {\n"
             "  baz();\n"
             "}",
             format("try{foo();}catch(...){baz();}", Style));
 
   Style.BraceWrapping.AfterFunction = true;
+  Style.BraceWrapping.AfterStruct = false;
   Style.BraceWrapping.AfterControlStatement = FormatStyle::BWACS_MultiLine;
   Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_All;
   Style.ColumnLimit = 80;
   verifyFormat("void shortfunction() { bar(); }", Style);
+  verifyFormat("struct T shortfunction() { return bar(); }", Style);
+  verifyFormat("struct T {};", Style);
 
   Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_None;
   verifyFormat("void shortfunction()\n"
                "{\n"
                "  bar();\n"
                "}",
                Style);
+  verifyFormat("struct T shortfunction()\n"
+               "{\n"
+               "  return bar();\n"
+               "}",
+               Style);
+  verifyFormat("struct T {};", Style);
+
+  Style.BraceWrapping.AfterFunction = false;
+  Style.BraceWrapping.AfterStruct = true;
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_All;
+  verifyFormat("void shortfunction() { bar(); }", Style);
+  verifyFormat("struct T shortfunction() { return bar(); }", Style);
+  verifyFormat("struct T\n"
+               "{\n"
+               "};",
+               Style);
+
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_None;
+  verifyFormat("void shortfunction() {\n"
+               "  bar();\n"
+               "}",
+               Style);
+  verifyFormat("struct T shortfunction() {\n"
+               "  return bar();\n"
+               "}",
+               Style);
+  verifyFormat("struct T\n"
+               "{\n"
+               "};",
+               Style);
 }
 
 TEST_F(FormatTest, BeforeWhile) {
   FormatStyle Style = getLLVMStyle();
   Style.BreakBeforeBraces = FormatStyle::BraceBreakingStyle::BS_Custom;
 
   verifyFormat("do {\n"
                "  foo();\n"