[clang-format]: Fix formatting of if statements with BlockIndent (#77699)

A bug with BlockIndent prevents line breaks within if (and else if)
clauses.

While fixing this bug, it appears that AlignAfterOpenBracket is not
designed to work with loop and if statements, but AlwaysBreak works on
if clauses. The documentation and tests are not clear on whether or not
this behavior is intended.

This PR preserves the `AlwaysBreak` behavior on `if` clauses without
supporting `BlockIndent` on `if` clauses to avoid regressions while
fixing the bug.

It may be reasonable to create an explicit option for alignment of if
(and loop) clauses intentionally for both `AlwaysBreak` and
`BlockIndent`

Fixes #54663.

Migrated from Differential Revision: https://reviews.llvm.org/D154755
See more discussion there. Addressed last open comment from the rev
about refactoring the complex conditional logic involved with the
`AlignAfterOpenBracket` line break behavior.

1 files changed, 17 insertions, 7 deletions

diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
index a099813..a3eb913 100644
--- a/clang/lib/Format/ContinuationIndenter.cpp
+++ b/clang/lib/Format/ContinuationIndenter.cpp
@@ -771,15 +771,25 @@ void ContinuationIndenter::addTokenOnCurrentLine(LineState &State, bool DryRun,
   // parenthesis by disallowing any further line breaks if there is no line
   // break after the opening parenthesis. Don't break if it doesn't conserve
   // columns.
+  auto IsOpeningBracket = [&](const FormatToken &Tok) {
+    auto IsStartOfBracedList = [&]() {
+      return Tok.is(tok::l_brace) && Tok.isNot(BK_Block) &&
+             Style.Cpp11BracedListStyle;
+    };
+    if (!Tok.isOneOf(tok::l_paren, TT_TemplateOpener, tok::l_square) &&
+        !IsStartOfBracedList()) {
+      return false;
+    }
+    if (!Tok.Previous)
+      return true;
+    if (Tok.Previous->isIf())
+      return Style.AlignAfterOpenBracket == FormatStyle::BAS_AlwaysBreak;
+    return !Tok.Previous->isOneOf(TT_CastRParen, tok::kw_for, tok::kw_while,
+                                  tok::kw_switch);
+  };
   if ((Style.AlignAfterOpenBracket == FormatStyle::BAS_AlwaysBreak ||
        Style.AlignAfterOpenBracket == FormatStyle::BAS_BlockIndent) &&
-      (Previous.isOneOf(tok::l_paren, TT_TemplateOpener, tok::l_square) ||
-       (Previous.is(tok::l_brace) && Previous.isNot(BK_Block) &&
-        Style.Cpp11BracedListStyle)) &&
-      State.Column > getNewLineColumn(State) &&
-      (!Previous.Previous ||
-       !Previous.Previous->isOneOf(TT_CastRParen, tok::kw_for, tok::kw_while,
-                                   tok::kw_switch)) &&
+      IsOpeningBracket(Previous) && State.Column > getNewLineColumn(State) &&
       // Don't do this for simple (no expressions) one-argument function calls
       // as that feels like needlessly wasting whitespace, e.g.:
       //