[clang-format] Indent tokens after hash only if it starts a line

Fixes #56602.

Differential Revision: https://reviews.llvm.org/D130136

clang/lib/Format/ContinuationIndenter.cpp

@@ -656,6 +656,7 @@ void ContinuationIndenter::addTokenOnCurrentLine(LineState &State, bool DryRun,
   int PPColumnCorrection = 0;
   if (Style.IndentPPDirectives == FormatStyle::PPDIS_AfterHash &&
       Previous.is(tok::hash) && State.FirstIndent > 0 &&
+      &Previous == State.Line->First &&
       (State.Line->Type == LT_PreprocessorDirective ||
        State.Line->Type == LT_ImportStatement)) {
     Spaces += State.FirstIndent;

clang/unittests/Format/FormatTest.cpp

@@ -5385,6 +5385,10 @@ TEST_F(FormatTest, IndentPreprocessorDirectives) {
                "#endif",
                Style);
   Style.IndentPPDirectives = FormatStyle::PPDIS_AfterHash;
+  verifyFormat("#if 1\n"
+               "#  define __STR(x) #x\n"
+               "#endif",
+               Style);
   verifyFormat("#ifdef _WIN32\n"
                "#  define A 0\n"
                "#  ifdef VAR2\n"