clang-format: Support `if CONSTEXPR` if CONSTEXPR is a macro.

[thakis]

Summary

This is like r305666 (which added support for if constexpr) except
that it allows a macro name after the if.

This is slightly tricky for two reasons:

1. r305666 didn't add test coverage for all cases where it added a kw_constexpr, so I had to figure out what all the added cases were for. I now added tests for all if constexpr bits that didn't have tests. (This took a while, see e.g. https://reviews.llvm.org/D65223)

2. Parsing if <ident> ( as an if means that #if defined( and #if __has_include( parse as ifs too. Add some special-case code to prevent this from happening where it's incorrect.

Fixes PR39248.

[klimek]

I am surprised this works as well as it does, but tests seem to indicate it does, so... LG (minus potentially reducing some duplication :)

clang/lib/Format/TokenAnnotator.cpp

2415

Do we want to pull out a function for the repeated condition?

[thakis]

Thanks, landing with your suggestion applied.

clang/lib/Format/ContinuationIndenter.cpp

if ((!BreakBeforeOperator && !(HasTwoOperands && Style.AlignOperands)) ||
         (!State.Stack.back().LastOperatorWrapped && BreakBeforeOperator))
       State.Stack.back().NoLineBreakInOperand = true;
   }
 
   State.Column += Spaces;
   if (Current.isNot(tok::comment) && Previous.is(tok::l_paren) &&
       Previous.Previous &&
       (Previous.Previous->isOneOf(tok::kw_if, tok::kw_for) ||
-       Previous.Previous->endsSequence(tok::kw_constexpr, tok::kw_if))) {
+       Previous.Previous->endsSequence(tok::kw_constexpr, tok::kw_if) ||
+       Previous.Previous->endsSequence(tok::identifier, tok::kw_if))) {
     // Treat the condition inside an if as if it was a second function
     // parameter, i.e. let nested calls have a continuation indent.
     State.Stack.back().LastSpace = State.Column;
     State.Stack.back().NestedBlockIndent = State.Column;
   } else if (!Current.isOneOf(tok::comment, tok::caret) &&
              ((Previous.is(tok::comma) &&
                !Previous.is(TT_OverloadedOperator)) ||
               (Previous.is(tok::colon) && Previous.is(TT_ObjCMethodExpr)))) {

clang/lib/Format/FormatToken.h

struct FormatToken {
   /// following the ``Next`` pointers, ignoring comments.
   template <typename A, typename... Ts>
   bool startsSequence(A K1, Ts... Tokens) const {
     return startsSequenceInternal(K1, Tokens...);
   }
 
   /// \c true if this token ends a sequence with the given tokens in order,
   /// following the ``Previous`` pointers, ignoring comments.
+  /// For example, given tokens [T1, T2, T3], the function returns true if
+  /// 3 tokens ending at this (ignoring comments) are [T3, T2, T1]. In other
+  /// words, the tokens passed to this function need to the reverse of the
+  /// order the tokens appear in code.
   template <typename A, typename... Ts>
   bool endsSequence(A K1, Ts... Tokens) const {
     return endsSequenceInternal(K1, Tokens...);
   }
 
   bool isStringLiteral() const { return tok::isStringLiteral(Tok.getKind()); }
 
   bool isObjCAtKeyword(tok::ObjCKeywordKind Kind) const {

clang/lib/Format/TokenAnnotator.cpp

if (Left->is(TT_OverloadedOperatorLParen)) {
       // type X = (...);
       // export type X = (...);
       Contexts.back().IsExpression = false;
     } else if (Left->Previous &&
                (Left->Previous->isOneOf(tok::kw_static_assert, tok::kw_decltype,
                                         tok::kw_if, tok::kw_while, tok::l_paren,
                                         tok::comma) ||
                 Left->Previous->endsSequence(tok::kw_constexpr, tok::kw_if) ||
+                Left->Previous->endsSequence(tok::identifier, tok::kw_if) ||
                 Left->Previous->is(TT_BinaryOperator))) {
       // static_assert, if and while usually contain expressions.
       Contexts.back().IsExpression = true;
     } else if (Style.Language == FormatStyle::LK_JavaScript && Left->Previous &&
                (Left->Previous->is(Keywords.kw_function) ||
                 (Left->Previous->endsSequence(tok::identifier,
                                               Keywords.kw_function)))) {
       // function(...) or function f(...)
case tok::amp:
       // | and & in declarations/type expressions represent union and
       // intersection types, respectively.
       if (Style.Language == FormatStyle::LK_JavaScript &&
           !Contexts.back().IsExpression)
         Tok->Type = TT_JsTypeOperator;
       break;
     case tok::kw_if:
     case tok::kw_while:
+      assert(!Line.startsWith(tok::hash));
       if (Tok->is(tok::kw_if) && CurrentToken &&
-          CurrentToken->is(tok::kw_constexpr))
+          CurrentToken->isOneOf(tok::kw_constexpr, tok::identifier))
         next();
       if (CurrentToken && CurrentToken->is(tok::l_paren)) {
         next();
         if (!parseParens(/*LookForDecls=*/true))
           return false;
       }
       break;
     case tok::kw_for:
case tok::pp_warning:
       parseWarningOrError();
       break;
     case tok::pp_pragma:
       parsePragma();
       break;
     case tok::pp_if:
     case tok::pp_elif:
       Contexts.back().IsExpression = true;
+      next();
       parseLine();
       break;
     default:
       break;
     }
     while (CurrentToken) {
       FormatToken *Tok = CurrentToken;
       next();
unsigned TokenAnnotator::splitPenalty(const AnnotatedLine &Line,
   if (Line.Type == LT_ObjCDecl && Left.is(tok::l_paren) && Left.Previous &&
       Left.Previous->isOneOf(tok::identifier, tok::greater))
     return 500;
 
   if (Left.is(tok::l_paren) && InFunctionDecl &&
       Style.AlignAfterOpenBracket != FormatStyle::BAS_DontAlign)
     return 100;
   if (Left.is(tok::l_paren) && Left.Previous &&
       (Left.Previous->isOneOf(tok::kw_if, tok::kw_for) ||
-       Left.Previous->endsSequence(tok::kw_constexpr, tok::kw_if)))
+       Left.Previous->endsSequence(tok::kw_constexpr, tok::kw_if) ||
+       Left.Previous->endsSequence(tok::identifier, tok::kw_if)))
     return 1000;
   if (Left.is(tok::equal) && InFunctionDecl)
     return 110;
   if (Right.is(tok::r_brace))
     return 1;
   if (Left.is(TT_TemplateOpener))
     return 100;
   if (Left.opensScope()) {
if ((Left.is(tok::r_paren) && Left.is(TT_AttributeParen)) ||
         (Left.is(tok::r_square) && Left.is(TT_AttributeSquare)))
       return true;
     return Line.Type == LT_ObjCDecl || Left.is(tok::semi) ||
            (Style.SpaceBeforeParens != FormatStyle::SBPO_Never &&
             (Left.isOneOf(tok::kw_if, tok::pp_elif, tok::kw_for, tok::kw_while,
                           tok::kw_switch, tok::kw_case, TT_ForEachMacro,
                           TT_ObjCForIn) ||
              Left.endsSequence(tok::kw_constexpr, tok::kw_if) ||
+             (Left.endsSequence(tok::identifier, tok::kw_if) &&
+              Line.Type != LT_PreprocessorDirective) ||
              (Left.isOneOf(tok::kw_try, Keywords.kw___except, tok::kw_catch,
                            tok::kw_new, tok::kw_delete) &&
               (!Left.Previous || Left.Previous->isNot(tok::period))))) ||
            (spaceRequiredBeforeParens(Right) &&
             (Left.is(tok::identifier) || Left.isFunctionLikeKeyword() ||
              Left.is(tok::r_paren) || Left.isSimpleTypeSpecifier() ||
              (Left.is(tok::r_square) && Left.MatchingParen &&
               Left.MatchingParen->is(TT_LambdaLSquare))) &&

clang/lib/Format/UnwrappedLineParser.cpp

       break;
     }
   } while (!eof());
 }
 
 void UnwrappedLineParser::parseIfThenElse() {
   assert(FormatTok->Tok.is(tok::kw_if) && "'if' expected");
   nextToken();
-  if (FormatTok->Tok.is(tok::kw_constexpr))
+  if (FormatTok->Tok.isOneOf(tok::kw_constexpr, tok::identifier))
     nextToken();
   if (FormatTok->Tok.is(tok::l_paren))
     parseParens();
   bool NeedsUnwrappedLine = false;
   if (FormatTok->Tok.is(tok::l_brace)) {
     CompoundStatementIndenter Indenter(this, Style, Line->Level);
     parseBlock(/*MustBeDeclaration=*/false);
     if (Style.BraceWrapping.BeforeElse)

clang/unittests/Format/FormatTest.cpp

 //===----------------------------------------------------------------------===//
 
 TEST_F(FormatTest, FormatIfWithoutCompoundStatement) {
   verifyFormat("if (true)\n  f();\ng();");
   verifyFormat("if (a)\n  if (b)\n    if (c)\n      g();\nh();");
   verifyFormat("if (a)\n  if (b) {\n    f();\n  }\ng();");
   verifyFormat("if constexpr (true)\n"
                "  f();\ng();");
+  verifyFormat("if CONSTEXPR (true)\n"
+               "  f();\ng();");
   verifyFormat("if constexpr (a)\n"
                "  if constexpr (b)\n"
                "    if constexpr (c)\n"
                "      g();\n"
                "h();");
+  verifyFormat("if CONSTEXPR (a)\n"
+               "  if CONSTEXPR (b)\n"
+               "    if CONSTEXPR (c)\n"
+               "      g();\n"
+               "h();");
   verifyFormat("if constexpr (a)\n"
                "  if constexpr (b) {\n"
                "    f();\n"
                "  }\n"
                "g();");
+  verifyFormat("if CONSTEXPR (a)\n"
+               "  if CONSTEXPR (b) {\n"
+               "    f();\n"
+               "  }\n"
+               "g();");
 
   FormatStyle AllowsMergedIf = getLLVMStyle();
   AllowsMergedIf.AlignEscapedNewlines = FormatStyle::ENAS_Left;
   AllowsMergedIf.AllowShortIfStatementsOnASingleLine =
       FormatStyle::SIS_WithoutElse;
   verifyFormat("if (a)\n"
                "  // comment\n"
                "  f();",

   AllowSimpleBracedStatements.AllowShortLoopsOnASingleLine = true;
 
   AllowSimpleBracedStatements.BreakBeforeBraces = FormatStyle::BS_Custom;
   AllowSimpleBracedStatements.BraceWrapping.AfterFunction = true;
   AllowSimpleBracedStatements.BraceWrapping.SplitEmptyRecord = false;
 
   verifyFormat("if (true) {}", AllowSimpleBracedStatements);
   verifyFormat("if constexpr (true) {}", AllowSimpleBracedStatements);
+  verifyFormat("if CONSTEXPR (true) {}", AllowSimpleBracedStatements);
   verifyFormat("while (true) {}", AllowSimpleBracedStatements);
   verifyFormat("for (;;) {}", AllowSimpleBracedStatements);
   verifyFormat("if (true) { f(); }", AllowSimpleBracedStatements);
   verifyFormat("if constexpr (true) { f(); }", AllowSimpleBracedStatements);
+  verifyFormat("if CONSTEXPR (true) { f(); }", AllowSimpleBracedStatements);
   verifyFormat("while (true) { f(); }", AllowSimpleBracedStatements);
   verifyFormat("for (;;) { f(); }", AllowSimpleBracedStatements);
   verifyFormat("if (true) {\n"
                "  ffffffffffffffffffffffffffffffffffffffffffffffffffffff();\n"
                "}",
                AllowSimpleBracedStatements);
   verifyFormat("if (true) { //\n"
                "  f();\n"

 
   AllowSimpleBracedStatements.AllowShortIfStatementsOnASingleLine =
       FormatStyle::SIS_WithoutElse;
   AllowSimpleBracedStatements.AllowShortLoopsOnASingleLine = true;
   AllowSimpleBracedStatements.BraceWrapping.AfterControlStatement = true;
 
   verifyFormat("if (true) {}", AllowSimpleBracedStatements);
   verifyFormat("if constexpr (true) {}", AllowSimpleBracedStatements);
+  verifyFormat("if CONSTEXPR (true) {}", AllowSimpleBracedStatements);
   verifyFormat("while (true) {}", AllowSimpleBracedStatements);
   verifyFormat("for (;;) {}", AllowSimpleBracedStatements);
   verifyFormat("if (true) { f(); }", AllowSimpleBracedStatements);
   verifyFormat("if constexpr (true) { f(); }", AllowSimpleBracedStatements);
+  verifyFormat("if CONSTEXPR (true) { f(); }", AllowSimpleBracedStatements);
   verifyFormat("while (true) { f(); }", AllowSimpleBracedStatements);
   verifyFormat("for (;;) { f(); }", AllowSimpleBracedStatements);
   verifyFormat("if (true)\n"
                "{\n"
                "  ffffffffffffffffffffffffffffffffffffffffffffffffffffff();\n"
                "}",
                AllowSimpleBracedStatements);
   verifyFormat("if (true)\n"

                "    } else {\n"
                "      g();\n"
                "    }\n"
                "  else\n"
                "    h();\n"
                "else {\n"
                "  i();\n"
                "}");
+  verifyFormat("if (true)\n"
+               "  if CONSTEXPR (true)\n"
+               "    if (true) {\n"
+               "      if CONSTEXPR (true)\n"
+               "        f();\n"
+               "    } else {\n"
+               "      g();\n"
+               "    }\n"
+               "  else\n"
+               "    h();\n"
+               "else {\n"
+               "  i();\n"
+               "}");
   verifyFormat("void f() {\n"
                "  if (a) {\n"
                "  } else {\n"
                "  }\n"
                "}");
 }
 
 TEST_F(FormatTest, ElseIf) {
   verifyFormat("if (a) {\n} else if (b) {\n}");
   verifyFormat("if (a)\n"
                "  f();\n"
                "else if (b)\n"
                "  g();\n"
                "else\n"
                "  h();");
   verifyFormat("if constexpr (a)\n"
                "  f();\n"
                "else if constexpr (b)\n"
                "  g();\n"
                "else\n"
                "  h();");
+  verifyFormat("if CONSTEXPR (a)\n"
+               "  f();\n"
+               "else if CONSTEXPR (b)\n"
+               "  g();\n"
+               "else\n"
+               "  h();");
   verifyFormat("if (a) {\n"
                "  f();\n"
                "}\n"
                "// or else ..\n"
                "else {\n"
                "  g()\n"
                "}");
 
   verifyFormat("if (a) {\n"
                "} else if (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(\n"
                "               aaaaaaaaaaaaaaaaaaaaaaaaaaaa)) {\n"
                "}");
+  verifyFormat("if (a) {\n"
+               "} else if constexpr (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(\n"
+               "                         aaaaaaaaaaaaaaaaaaaaaaaaaaaa)) {\n"
+               "}");
+  verifyFormat("if (a) {\n"
+               "} else if CONSTEXPR (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(\n"
+               "                         aaaaaaaaaaaaaaaaaaaaaaaaaaaa)) {\n"
+               "}");
   verifyFormat("if (a) {\n"
                "} else if (\n"
                "    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa) {\n"
                "}",
                getLLVMStyleWithColumns(62));
   verifyFormat("if (a) {\n"
                "} else if constexpr (\n"
                "    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa) {\n"
                "}",
                getLLVMStyleWithColumns(62));
+  verifyFormat("if (a) {\n"
+               "} else if CONSTEXPR (\n"
+               "    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa) {\n"
+               "}",
+               getLLVMStyleWithColumns(62));
 }
 
 TEST_F(FormatTest, FormatsForLoop) {
   verifyFormat(
       "for (int VeryVeryLongLoopVariable = 0; VeryVeryLongLoopVariable < 10;\n"
       "     ++VeryVeryLongLoopVariable)\n"
       "  ;");
   verifyFormat("for (;;)\n"

                "    1);");
 
   verifyFormat("if ((aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa ||\n"
                "     bbbbbbbbbbbbbbbbbb) && // aaaaaaaaaaaaaaaa\n"
                "    cccccc) {\n}");
   verifyFormat("if constexpr ((aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa ||\n"
                "               bbbbbbbbbbbbbbbbbb) && // aaaaaaaaaaa\n"
                "              cccccc) {\n}");
+  verifyFormat("if CONSTEXPR ((aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa ||\n"
+               "               bbbbbbbbbbbbbbbbbb) && // aaaaaaaaaaa\n"
+               "              cccccc) {\n}");
   verifyFormat("b = a &&\n"
                "    // Comment\n"
                "    b.c && d;");
 
   // If the LHS of a comparison is not a binary expression itself, the
   // additional linebreak confuses many people.
   verifyFormat(
       "if (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(\n"

   verifyFormat("if (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa ==\n"
                "    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa *\n"
                "            aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa +\n"
                "        bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb) {\n}");
   verifyFormat("if () {\n"
                "} else if (aaaaa && bbbbb > // break\n"
                "                        ccccc) {\n"
                "}");
+  verifyFormat("if () {\n"
+               "} else if constexpr (aaaaa && bbbbb > // break\n"
+               "                                  ccccc) {\n"
+               "}");
+  verifyFormat("if () {\n"
+               "} else if CONSTEXPR (aaaaa && bbbbb > // break\n"
+               "                                  ccccc) {\n"
+               "}");
   verifyFormat("if () {\n"
                "} else if (aaaaa &&\n"
                "           bbbbb > // break\n"
                "               ccccc &&\n"
                "           ddddd) {\n"
                "}");
 
   // Presence of a trailing comment used to change indentation of b.

       "int *MyValues = {\n"
       "    *A, // Operator detection might be confused by the '{'\n"
       "    *BB // Operator detection might be confused by previous comment\n"
       "};");
 
   verifyIndependentOfContext("if (int *a = &b)");
   verifyIndependentOfContext("if (int &a = *b)");
   verifyIndependentOfContext("if (a & b[i])");
+  verifyIndependentOfContext("if constexpr (a & b[i])");
+  verifyIndependentOfContext("if CONSTEXPR (a & b[i])");
   verifyIndependentOfContext("if (a * (b * c))");
+  verifyIndependentOfContext("if constexpr (a * (b * c))");
+  verifyIndependentOfContext("if CONSTEXPR (a * (b * c))");
   verifyIndependentOfContext("if (a::b::c::d & b[i])");
   verifyIndependentOfContext("if (*b[i])");
   verifyIndependentOfContext("if (int *a = (&b))");
   verifyIndependentOfContext("while (int *a = &b)");
   verifyIndependentOfContext("while (a * (b * c))");
   verifyIndependentOfContext("size = sizeof *a;");
   verifyIndependentOfContext("if (a && (b = c))");
   verifyFormat("void f() {\n"

                "  // Comment\n"
                "  if (true) continue;\n"
                "}",
                ShortMergedIf);
   ShortMergedIf.ColumnLimit = 33;
   verifyFormat("#define A \\\n"
                "  if constexpr (true) return 42;",
                ShortMergedIf);
+  verifyFormat("#define A \\\n"
+               "  if CONSTEXPR (true) return 42;",
+               ShortMergedIf);
   ShortMergedIf.ColumnLimit = 29;
   verifyFormat("#define A                   \\\n"
                "  if (aaaaaaaaaa) return 1; \\\n"
                "  return 2;",
                ShortMergedIf);
   ShortMergedIf.ColumnLimit = 28;
   verifyFormat("#define A         \\\n"
                "  if (aaaaaaaaaa) \\\n"
                "    return 1;     \\\n"
                "  return 2;",
                ShortMergedIf);
   verifyFormat("#define A                \\\n"
                "  if constexpr (aaaaaaa) \\\n"
                "    return 1;            \\\n"
                "  return 2;",
                ShortMergedIf);
+  verifyFormat("#define A                \\\n"
+               "  if CONSTEXPR (aaaaaaa) \\\n"
+               "    return 1;            \\\n"
+               "  return 2;",
+               ShortMergedIf);
 }
 
 TEST_F(FormatTest, FormatStarDependingOnContext) {
   verifyFormat("void f(int *a);");
   verifyFormat("void f() { f(fint * b); }");
   verifyFormat("class A {\n  void f(int *a);\n};");
   verifyFormat("class A {\n  int *a;\n};");
   verifyFormat("namespace a {\n"

   verifyFormat("void f(bool b)\n"
                "{\n"
                "  if constexpr (b)\n"
                "  {\n"
                "    return;\n"
                "  }\n"
                "}\n",
                BreakBeforeBraceShortIfs);
+  verifyFormat("void f(bool b)\n"
+               "{\n"
+               "  if CONSTEXPR (b)\n"
+               "  {\n"
+               "    return;\n"
+               "  }\n"
+               "}\n",
+               BreakBeforeBraceShortIfs);
   verifyFormat("void f(bool b)\n"
                "{\n"
                "  if (b) return;\n"
                "}\n",
                BreakBeforeBraceShortIfs);
   verifyFormat("void f(bool b)\n"
                "{\n"
                "  if constexpr (b) return;\n"
                "}\n",
                BreakBeforeBraceShortIfs);
+  verifyFormat("void f(bool b)\n"
+               "{\n"
+               "  if CONSTEXPR (b) return;\n"
+               "}\n",
+               BreakBeforeBraceShortIfs);
   verifyFormat("void f(bool b)\n"
                "{\n"
                "  while (b)\n"
                "  {\n"
                "    return;\n"
                "  }\n"
                "}\n",
                BreakBeforeBraceShortIfs);

                "      doo_dah();\n"
                "    })) {\n"
                "}");
   verifyFormat("if constexpr (blah_blah(whatever, whatever, [] {\n"
                "                doo_dah();\n"
                "                doo_dah();\n"
                "              })) {\n"
                "}");
+  verifyFormat("if CONSTEXPR (blah_blah(whatever, whatever, [] {\n"
+               "                doo_dah();\n"
+               "                doo_dah();\n"
+               "              })) {\n"
+               "}");
   verifyFormat("auto lambda = []() {\n"
                "  int a = 2\n"
                "#if A\n"
                "          + 2\n"
                "#endif\n"
                "      ;\n"
                "};");