[clang-format] Fix a bug in DerivePointerAlignment fallback

[owenpan]

Summary

Fixes https://github.com/llvm/llvm-project/issues/59953.

clang/lib/Format/Format.cpp

for (AnnotatedLine *Line : AnnotatedLines) {
           HasBinPackedFunction = true;
         if (Tok->is(PPK_OnePerLine))
           HasOnePerLineFunction = true;
 
         Tok = Tok->Next;
       }
     }
     if (Style.DerivePointerAlignment) {
-      Style.PointerAlignment = countVariableAlignments(AnnotatedLines) <= 0
-                                   ? FormatStyle::PAS_Left
-                                   : FormatStyle::PAS_Right;
+      const auto NetRightCount = countVariableAlignments(AnnotatedLines);
+      if (NetRightCount > 0)
+        Style.PointerAlignment = FormatStyle::PAS_Right;
+      else if (NetRightCount < 0)
+        Style.PointerAlignment = FormatStyle::PAS_Left;
       Style.ReferenceAlignment = FormatStyle::RAS_Pointer;
     }
     if (Style.Standard == FormatStyle::LS_Auto) {
       Style.Standard = hasCpp03IncompatibleFormat(AnnotatedLines)
                            ? FormatStyle::LS_Latest
                            : FormatStyle::LS_Cpp03;
     }
     BinPackInconclusiveFunctions =

clang/unittests/Format/FormatTest.cpp

TEST_F(FormatTest, UnderstandsFunctionRefQualification) {
   verifyFormat(Prefix + "int *x;", DerivePointerAlignment);
   // However a space between cv-qualifiers and ref-qualifiers *is* evidence.
   Prefix = "void a() const &;\n"
            "void b() const &;\n";
   EXPECT_EQ(Prefix + "int *x;",
             format(Prefix + "int* x;", DerivePointerAlignment));
 }
 
+TEST_F(FormatTest, PointerAlignmentFallback) {
+  FormatStyle Style = getLLVMStyle();
+  Style.DerivePointerAlignment = true;
+
+  const StringRef Code("int* p;\n"
+                       "int *q;\n"
+                       "int * r;");
+
+  EXPECT_EQ(Style.PointerAlignment, FormatStyle::PAS_Right);
+  verifyFormat("int *p;\n"
+               "int *q;\n"
+               "int *r;",
+               Code, Style);
+
+  Style.PointerAlignment = FormatStyle::PAS_Left;
+  verifyFormat("int* p;\n"
+               "int* q;\n"
+               "int* r;",
+               Code, Style);
+
+  Style.PointerAlignment = FormatStyle::PAS_Middle;
+  verifyFormat("int * p;\n"
+               "int * q;\n"
+               "int * r;",
+               Code, Style);
+}
+
 TEST_F(FormatTest, UnderstandsNewAndDelete) {
   verifyFormat("void f() {\n"
                "  A *a = new A;\n"
                "  A *a = new (placement) A;\n"
                "  delete a;\n"
                "  delete (A *)a;\n"
                "}");
   verifyFormat("new (aaaaaaaaaaaaaaaaaaaaaaaaaa(aaaaaaaaaaaaaaaaaaaaaaa))\n"