[clang-format] Fix consecutive alignments in #else blocks

Since 3.8 or earlier, clang-format has been lumping all #else, #elif,
etc blocks together when doing whitespace replacements and causing
consecutive alignments across #else blocks.

Commit c077975 partially addressed the problem but also triggered
"regressions".

This patch fixes the root cause of the problem and "reverts" c077975
(except for the unit tests).

Fixes #36070.
Fixes #55265.
Fixes #60721.
Fixes #61498.

Differential Revision: https://reviews.llvm.org/D150057

clang/lib/Format/WhitespaceManager.cpp

@@ -49,8 +49,16 @@ void WhitespaceManager::replaceWhitespace(FormatToken &Tok, unsigned Newlines,
                                           unsigned Spaces,
                                           unsigned StartOfTokenColumn,
                                           bool IsAligned, bool InPPDirective) {
-  if (Tok.Finalized || (Tok.MacroCtx && Tok.MacroCtx->Role == MR_ExpandedArg))
+  auto PPBranchDirectiveStartsLine = [&Tok] {
+    return Tok.is(tok::hash) && !Tok.Previous && Tok.Next &&
+           Tok.Next->isOneOf(tok::pp_if, tok::pp_ifdef, tok::pp_ifndef,
+                             tok::pp_elif, tok::pp_elifdef, tok::pp_elifndef,
+                             tok::pp_else, tok::pp_endif);
+  };
+  if ((Tok.Finalized && !PPBranchDirectiveStartsLine()) ||
+      (Tok.MacroCtx && Tok.MacroCtx->Role == MR_ExpandedArg)) {
     return;
+  }
   Tok.setDecision((Newlines > 0) ? FD_Break : FD_Continue);
   Changes.push_back(Change(Tok, /*CreateReplacement=*/true, Tok.WhitespaceRange,
                            Spaces, StartOfTokenColumn, Newlines, "", "",
@@ -522,13 +530,6 @@ static unsigned AlignTokens(const FormatStyle &Style, F &&Matches,
                                    ? Changes[StartAt].indentAndNestingLevel()
                                    : std::tuple<unsigned, unsigned, unsigned>();
 
-  // Keep track if the first token has a non-zero indent and nesting level.
-  // This can happen when aligning the contents of "#else" preprocessor blocks,
-  // which is done separately.
-  bool HasInitialIndentAndNesting =
-      StartAt == 0 &&
-      IndentAndNestingLevel > std::tuple<unsigned, unsigned, unsigned>();
-
   // Keep track of the number of commas before the matching tokens, we will only
   // align a sequence of matching tokens if they are preceded by the same number
   // of commas.
@@ -563,19 +564,8 @@ static unsigned AlignTokens(const FormatStyle &Style, F &&Matches,
 
   unsigned i = StartAt;
   for (unsigned e = Changes.size(); i != e; ++i) {
-    if (Changes[i].indentAndNestingLevel() < IndentAndNestingLevel) {
-      if (!HasInitialIndentAndNesting)
-        break;
-      // The contents of preprocessor blocks are aligned separately.
-      // If the initial preprocessor block is indented or nested (e.g. it's in
-      // a function), do not align and exit after finishing this scope block.
-      // Instead, align, and then lower the baseline indent and nesting level
-      // in order to continue aligning subsequent blocks.
-      EndOfSequence = i;
-      AlignCurrentSequence();
-      IndentAndNestingLevel =
-          Changes[i].indentAndNestingLevel(); // new baseline
-    }
+    if (Changes[i].indentAndNestingLevel() < IndentAndNestingLevel)
+      break;
 
     if (Changes[i].NewlinesBefore != 0) {
       CommasBeforeMatch = 0;

clang/unittests/Format/FormatTest.cpp

@@ -6367,6 +6367,51 @@ TEST_F(FormatTest, FormatAlignInsidePreprocessorElseBlock) {
                "#endif\n"
                "}",
                Style);
+
+  verifyFormat("#if FOO\n"
+               "int a = 1;\n"
+               "#else\n"
+               "int ab = 2;\n"
+               "#endif\n"
+               "#ifdef BAR\n"
+               "int abc = 3;\n"
+               "#elifdef BAZ\n"
+               "int abcd = 4;\n"
+               "#endif",
+               Style);
+
+  verifyFormat("void f() {\n"
+               "  if (foo) {\n"
+               "#if FOO\n"
+               "    int a = 1;\n"
+               "#else\n"
+               "    bool a = true;\n"
+               "#endif\n"
+               "    int abc = 3;\n"
+               "#ifndef BAR\n"
+               "    int abcd = 4;\n"
+               "#elif BAZ\n"
+               "    bool abcd = true;\n"
+               "#endif\n"
+               "  }\n"
+               "}",
+               Style);
+
+  verifyFormat("void f() {\n"
+               "#if FOO\n"
+               "  a = 1;\n"
+               "#else\n"
+               "  ab = 2;\n"
+               "#endif\n"
+               "}\n"
+               "void g() {\n"
+               "#if BAR\n"
+               "  abc = 3;\n"
+               "#elifndef BAZ\n"
+               "  abcd = 4;\n"
+               "#endif\n"
+               "}",
+               Style);
 }
 
 TEST_F(FormatTest, FormatHashIfNotAtStartOfLine) {

clang/unittests/Format/FormatTestComments.cpp

@@ -2759,7 +2759,7 @@ TEST_F(FormatTestComments, AlignTrailingComments) {
 
   // Checks an edge case in preprocessor handling.
   // These comments should *not* be aligned
-  EXPECT_NE( // change for EQ when fixed
+  EXPECT_EQ(
       "#if FOO\n"
       "#else\n"
       "long a; // Line about a\n"
@@ -4316,7 +4316,7 @@ TEST_F(FormatTestComments, SplitCommentIntroducers) {
 )",
             format(R"(//
 /\
-/ 
+/
   )",
                    getLLVMStyleWithColumns(10)));
 }