[clang-format][PR41899] PointerAlignment: Left leads to useless space in lambda intializer expression

[MyDeveloperDay]

Summary

https://bugs.llvm.org/show_bug.cgi?id=41899

auto lambda = [&a = a]() { a = 2; };

is formatted as

auto lambda = [& a = a]() { a = 2; };

With an extra space if PointerAlignment is set to Left

The space "& a" looks strange when there is no type in the lambda's intializer expression. This can be worked around with by setting "PointerAlignment: Right", but ideally "PointerAlignment: Left" would not add a space in this case.

[klimek]

LG

clang/lib/Format/TokenAnnotator.cpp

return Right.Tok.isLiteral() || Right.is(TT_BlockComment) ||
            (Right.isOneOf(Keywords.kw_override, Keywords.kw_final) &&
             !Right.is(TT_StartOfName)) ||
            (Right.is(tok::l_brace) && Right.BlockKind == BK_Block) ||
            (!Right.isOneOf(TT_PointerOrReference, TT_ArraySubscriptLSquare,
                            tok::l_paren) &&
             (Style.PointerAlignment != FormatStyle::PAS_Right &&
              !Line.IsMultiVariableDeclStmt) &&
             Left.Previous &&
-            !Left.Previous->isOneOf(tok::l_paren, tok::coloncolon));
+            !Left.Previous->isOneOf(tok::l_paren, tok::coloncolon,
+                                    tok::l_square));
   if (Right.is(tok::star) && Left.is(tok::l_paren))
     return false;
   const auto SpaceRequiredForArrayInitializerLSquare =
       [](const FormatToken &LSquareTok, const FormatStyle &Style) {
         return Style.SpacesInContainerLiterals ||
                ((Style.Language == FormatStyle::LK_Proto ||
                  Style.Language == FormatStyle::LK_TextProto) &&
                 !Style.Cpp11BracedListStyle &&

clang/unittests/Format/FormatTest.cpp

TEST_F(FormatTest, TypenameMacros) {
   verifyFormat("for (LIST(int) *a = NULL; a;) {\n}", Macros);
   verifyFormat("STACK_OF(int) f(LIST(int) *arg);", Macros);
 
   Macros.PointerAlignment = FormatStyle::PAS_Left;
   verifyFormat("STACK_OF(int)* a;", Macros);
   verifyFormat("STACK_OF(int*)* a;", Macros);
 }
 
+TEST_F(FormatTest, AmbersandInLamda) {
+  // Test case reported in https://bugs.llvm.org/show_bug.cgi?id=41899
+  FormatStyle AlignStyle = getLLVMStyle();
+  AlignStyle.PointerAlignment = FormatStyle::PAS_Left;
+  verifyFormat("auto lambda = [&a = a]() { a = 2; };", AlignStyle);
+  AlignStyle.PointerAlignment = FormatStyle::PAS_Right;
+  verifyFormat("auto lambda = [&a = a]() { a = 2; };", AlignStyle);
+}
+
 } // end namespace
 } // end namespace format
 } // end namespace clang