[clang-format] Make AlwaysBreakAfterReturnType work with K&R C function definitions

[owenpan]

Summary

See PR50999.

[MyDeveloperDay]

Thanks for this, I'm not sure I have the heart to dig out my old K&R code to test it ;-), Assuming the tests are good then it LGTM.

[MyDeveloperDay]

Myabe give the others some time to take a look too

[curdeius]

LGTM.

clang/lib/Format/TokenAnnotator.cpp

static bool isFunctionDeclarationName(const FormatToken &Current,
   if (Line.Last->is(tok::l_brace))
     return true;
   if (Next->Next == Next->MatchingParen)
     return true; // Empty parentheses.
   // If there is an &/&& after the r_paren, this is likely a function.
   if (Next->MatchingParen->Next &&
       Next->MatchingParen->Next->is(TT_PointerOrReference))
     return true;
+  // Check for K&R C function definitions, e.g.:
+  //   int f(i)
+  //   {
+  //     return i + 1;
+  //   }
+  if (Next->Next && Next->Next->is(tok::identifier) &&
+      !(Next->MatchingParen->Next && Next->MatchingParen->Next->is(tok::semi)))
+    return true;
   for (const FormatToken *Tok = Next->Next; Tok && Tok != Next->MatchingParen;
        Tok = Tok->Next) {
     if (Tok->is(TT_TypeDeclarationParen))
       return true;
     if (Tok->isOneOf(tok::l_paren, TT_TemplateOpener) && Tok->MatchingParen) {
       Tok = Tok->MatchingParen;
       continue;
     }

clang/unittests/Format/FormatTest.cpp

verifyFormat("int\n"
                Style);
   verifyFormat("int\n"
                "foo(A<B<8>, 8> a)\n"
                "{\n"
                "  return a;\n"
                "}\n",
                Style);
 
+  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
+  Style.BraceWrapping.AfterFunction = true;
+  verifyFormat("int f(i);\n" // No break here.
+               "int\n"       // Break here.
+               "f(i)\n"
+               "{\n"
+               "  return i + 1;\n"
+               "}\n",
+               Style);
+
   Style = getGNUStyle();
 
   // Test for comments at the end of function declarations.
   verifyFormat("void\n"
                "foo (int a, /*abc*/ int b) // def\n"
                "{\n"
                "}\n",
                Style);