[clang][ASTMatcher] Add matchers for CXXFoldExpr (#71245)

Adds support for the following matchers related to `CXXFoldExpr`:
`cxxFoldExpr`, `callee`,
  `hasInit`, `hasPattern`, `isRightFold`, `isLeftFold`,
  `isUnaryFold`, `isBinaryFold`, `hasOperator`, `hasLHS`, `hasRHS`.

Author: 5chmidti

clang/docs/LibASTMatchersReference.html

@@ -1123,6 +1123,9 @@ AST Matchers
 - Add ``convertVectorExpr``.
 - Add ``dependentSizedExtVectorType``.
 - Add ``macroQualifiedType``.
+- Add ``CXXFoldExpr`` related matchers: ``cxxFoldExpr``, ``callee``,
+  ``hasInit``, ``hasPattern``, ``isRightFold``, ``isLeftFold``,
+  ``isUnaryFold``, ``isBinaryFold``, ``hasOperator``, ``hasLHS``, ``hasRHS``, ``hasEitherOperand``.
 
 clang-format
 ------------

clang/docs/ReleaseNotes.rst

@@ -2062,6 +2062,18 @@ extern const internal::VariadicDynCastAllOfMatcher<Stmt, CXXDefaultArgExpr>
 extern const internal::VariadicDynCastAllOfMatcher<Stmt, CXXOperatorCallExpr>
     cxxOperatorCallExpr;
 
+/// Matches C++17 fold expressions.
+///
+/// Example matches `(0 + ... + args)`:
+/// \code
+///   template <typename... Args>
+///   auto sum(Args... args) {
+///       return (0 + ... + args);
+///   }
+/// \endcode
+extern const internal::VariadicDynCastAllOfMatcher<Stmt, CXXFoldExpr>
+    cxxFoldExpr;
+
 /// Matches rewritten binary operators
 ///
 /// Example matches use of "<":
@@ -3881,7 +3893,7 @@ AST_MATCHER_P(ObjCMessageExpr, numSelectorArgs, unsigned, N) {
   return Node.getSelector().getNumArgs() == N;
 }
 
-/// Matches if the call expression's callee expression matches.
+/// Matches if the call or fold expression's callee expression matches.
 ///
 /// Given
 /// \code
@@ -3893,13 +3905,32 @@ AST_MATCHER_P(ObjCMessageExpr, numSelectorArgs, unsigned, N) {
 /// with callee(...)
 ///   matching this->x, x, y.x, f respectively
 ///
+/// Given
+/// \code
+///   template <typename... Args>
+///   auto sum(Args... args) {
+///       return (0 + ... + args);
+///   }
+///
+///   template <typename... Args>
+///   auto multiply(Args... args) {
+///       return (args * ... * 1);
+///   }
+/// \endcode
+/// cxxFoldExpr(callee(expr()))
+///   matches (args * ... * 1)
+/// with callee(...)
+///   matching *
+///
 /// Note: Callee cannot take the more general internal::Matcher<Expr>
 /// because this introduces ambiguous overloads with calls to Callee taking a
 /// internal::Matcher<Decl>, as the matcher hierarchy is purely
 /// implemented in terms of implicit casts.
-AST_MATCHER_P(CallExpr, callee, internal::Matcher<Stmt>,
-              InnerMatcher) {
-  const Expr *ExprNode = Node.getCallee();
+AST_POLYMORPHIC_MATCHER_P_OVERLOAD(callee,
+                                   AST_POLYMORPHIC_SUPPORTED_TYPES(CallExpr,
+                                                                   CXXFoldExpr),
+                                   internal::Matcher<Stmt>, InnerMatcher, 0) {
+  const auto *ExprNode = Node.getCallee();
   return (ExprNode != nullptr &&
           InnerMatcher.matches(*ExprNode, Finder, Builder));
 }
@@ -4532,6 +4563,121 @@ AST_POLYMORPHIC_MATCHER_P2(hasArgument,
   return InnerMatcher.matches(*Arg->IgnoreParenImpCasts(), Finder, Builder);
 }
 
+/// Matches the operand that does not contain the parameter pack.
+///
+/// Example matches `(0 + ... + args)` and `(args * ... * 1)`
+///     (matcher = cxxFoldExpr(hasFoldInit(expr())))
+///   with hasFoldInit(...)
+///     matching `0` and `1` respectively
+/// \code
+///   template <typename... Args>
+///   auto sum(Args... args) {
+///       return (0 + ... + args);
+///   }
+///
+///   template <typename... Args>
+///   auto multiply(Args... args) {
+///       return (args * ... * 1);
+///   }
+/// \endcode
+AST_MATCHER_P(CXXFoldExpr, hasFoldInit, ast_matchers::internal::Matcher<Expr>,
+              InnerMacher) {
+  const auto *const Init = Node.getInit();
+  return Init && InnerMacher.matches(*Init, Finder, Builder);
+}
+
+/// Matches the operand that contains the parameter pack.
+///
+/// Example matches `(0 + ... + args)`
+///     (matcher = cxxFoldExpr(hasPattern(expr())))
+///   with hasPattern(...)
+///     matching `args`
+/// \code
+///   template <typename... Args>
+///   auto sum(Args... args) {
+///       return (0 + ... + args);
+///   }
+///
+///   template <typename... Args>
+///   auto multiply(Args... args) {
+///       return (args * ... * 1);
+///   }
+/// \endcode
+AST_MATCHER_P(CXXFoldExpr, hasPattern, ast_matchers::internal::Matcher<Expr>,
+              InnerMacher) {
+  const Expr *const Pattern = Node.getPattern();
+  return Pattern && InnerMacher.matches(*Pattern, Finder, Builder);
+}
+
+/// Matches right-folding fold expressions.
+///
+/// Example matches `(args * ... * 1)`
+///     (matcher = cxxFoldExpr(isRightFold()))
+/// \code
+///   template <typename... Args>
+///   auto sum(Args... args) {
+///       return (0 + ... + args);
+///   }
+///
+///   template <typename... Args>
+///   auto multiply(Args... args) {
+///       return (args * ... * 1);
+///   }
+/// \endcode
+AST_MATCHER(CXXFoldExpr, isRightFold) { return Node.isRightFold(); }
+
+/// Matches left-folding fold expressions.
+///
+/// Example matches `(0 + ... + args)`
+///     (matcher = cxxFoldExpr(isLeftFold()))
+/// \code
+///   template <typename... Args>
+///   auto sum(Args... args) {
+///       return (0 + ... + args);
+///   }
+///
+///   template <typename... Args>
+///   auto multiply(Args... args) {
+///       return (args * ... * 1);
+///   }
+/// \endcode
+AST_MATCHER(CXXFoldExpr, isLeftFold) { return Node.isLeftFold(); }
+
+/// Matches unary fold expressions, i.e. fold expressions without an
+/// initializer.
+///
+/// Example matches `(args * ...)`
+///     (matcher = cxxFoldExpr(isUnaryFold()))
+/// \code
+///   template <typename... Args>
+///   auto sum(Args... args) {
+///       return (0 + ... + args);
+///   }
+///
+///   template <typename... Args>
+///   auto multiply(Args... args) {
+///       return (args * ...);
+///   }
+/// \endcode
+AST_MATCHER(CXXFoldExpr, isUnaryFold) { return Node.getInit() == nullptr; }
+
+/// Matches binary fold expressions, i.e. fold expressions with an initializer.
+///
+/// Example matches `(0 + ... + args)`
+///     (matcher = cxxFoldExpr(isBinaryFold()))
+/// \code
+///   template <typename... Args>
+///   auto sum(Args... args) {
+///       return (0 + ... + args);
+///   }
+///
+///   template <typename... Args>
+///   auto multiply(Args... args) {
+///       return (args * ...);
+///   }
+/// \endcode
+AST_MATCHER(CXXFoldExpr, isBinaryFold) { return Node.getInit() != nullptr; }
+
 /// Matches the n'th item of an initializer list expression.
 ///
 /// Example matches y.
@@ -5709,17 +5855,27 @@ AST_POLYMORPHIC_MATCHER_P_OVERLOAD(equals,
     .matchesNode(Node);
 }
 
-/// Matches the operator Name of operator expressions (binary or
-/// unary).
+/// Matches the operator Name of operator expressions and fold expressions
+/// (binary or unary).
 ///
 /// Example matches a || b (matcher = binaryOperator(hasOperatorName("||")))
 /// \code
 ///   !(a || b)
 /// \endcode
+///
+/// Example matches `(0 + ... + args)`
+///     (matcher = cxxFoldExpr(hasOperatorName("+")))
+/// \code
+///   template <typename... Args>
+///   auto sum(Args... args) {
+///       return (0 + ... + args);
+///   }
+/// \endcode
 AST_POLYMORPHIC_MATCHER_P(
     hasOperatorName,
     AST_POLYMORPHIC_SUPPORTED_TYPES(BinaryOperator, CXXOperatorCallExpr,
-                                    CXXRewrittenBinaryOperator, UnaryOperator),
+                                    CXXRewrittenBinaryOperator, CXXFoldExpr,
+                                    UnaryOperator),
     std::string, Name) {
   if (std::optional<StringRef> OpName = internal::getOpName(Node))
     return *OpName == Name;
@@ -5789,11 +5945,12 @@ AST_POLYMORPHIC_MATCHER(
 /// \code
 ///   a || b
 /// \endcode
-AST_POLYMORPHIC_MATCHER_P(hasLHS,
-                          AST_POLYMORPHIC_SUPPORTED_TYPES(
-                              BinaryOperator, CXXOperatorCallExpr,
-                              CXXRewrittenBinaryOperator, ArraySubscriptExpr),
-                          internal::Matcher<Expr>, InnerMatcher) {
+AST_POLYMORPHIC_MATCHER_P(
+    hasLHS,
+    AST_POLYMORPHIC_SUPPORTED_TYPES(BinaryOperator, CXXOperatorCallExpr,
+                                    CXXRewrittenBinaryOperator,
+                                    ArraySubscriptExpr, CXXFoldExpr),
+    internal::Matcher<Expr>, InnerMatcher) {
   const Expr *LeftHandSide = internal::getLHS(Node);
   return (LeftHandSide != nullptr &&
           InnerMatcher.matches(*LeftHandSide, Finder, Builder));
@@ -5805,29 +5962,31 @@ AST_POLYMORPHIC_MATCHER_P(hasLHS,
 /// \code
 ///   a || b
 /// \endcode
-AST_POLYMORPHIC_MATCHER_P(hasRHS,
-                          AST_POLYMORPHIC_SUPPORTED_TYPES(
-                              BinaryOperator, CXXOperatorCallExpr,
-                              CXXRewrittenBinaryOperator, ArraySubscriptExpr),
-                          internal::Matcher<Expr>, InnerMatcher) {
+AST_POLYMORPHIC_MATCHER_P(
+    hasRHS,
+    AST_POLYMORPHIC_SUPPORTED_TYPES(BinaryOperator, CXXOperatorCallExpr,
+                                    CXXRewrittenBinaryOperator,
+                                    ArraySubscriptExpr, CXXFoldExpr),
+    internal::Matcher<Expr>, InnerMatcher) {
   const Expr *RightHandSide = internal::getRHS(Node);
   return (RightHandSide != nullptr &&
           InnerMatcher.matches(*RightHandSide, Finder, Builder));
 }
 
 /// Matches if either the left hand side or the right hand side of a
-/// binary operator matches.
+/// binary operator or fold expression matches.
 AST_POLYMORPHIC_MATCHER_P(
     hasEitherOperand,
     AST_POLYMORPHIC_SUPPORTED_TYPES(BinaryOperator, CXXOperatorCallExpr,
-                                    CXXRewrittenBinaryOperator),
+                                    CXXFoldExpr, CXXRewrittenBinaryOperator),
     internal::Matcher<Expr>, InnerMatcher) {
   return internal::VariadicDynCastAllOfMatcher<Stmt, NodeType>()(
              anyOf(hasLHS(InnerMatcher), hasRHS(InnerMatcher)))
       .matches(Node, Finder, Builder);
 }
 
-/// Matches if both matchers match with opposite sides of the binary operator.
+/// Matches if both matchers match with opposite sides of the binary operator
+/// or fold expression.
 ///
 /// Example matcher = binaryOperator(hasOperands(integerLiteral(equals(1),
 ///                                              integerLiteral(equals(2)))
@@ -5840,7 +5999,7 @@ AST_POLYMORPHIC_MATCHER_P(
 AST_POLYMORPHIC_MATCHER_P2(
     hasOperands,
     AST_POLYMORPHIC_SUPPORTED_TYPES(BinaryOperator, CXXOperatorCallExpr,
-                                    CXXRewrittenBinaryOperator),
+                                    CXXFoldExpr, CXXRewrittenBinaryOperator),
     internal::Matcher<Expr>, Matcher1, internal::Matcher<Expr>, Matcher2) {
   return internal::VariadicDynCastAllOfMatcher<Stmt, NodeType>()(
              anyOf(allOf(hasLHS(Matcher1), hasRHS(Matcher2)),

clang/include/clang/ASTMatchers/ASTMatchers.h

@@ -2195,6 +2195,9 @@ inline std::optional<StringRef> getOpName(const CXXOperatorCallExpr &Node) {
   }
   return BinaryOperator::getOpcodeStr(*optBinaryOpcode);
 }
+inline StringRef getOpName(const CXXFoldExpr &Node) {
+  return BinaryOperator::getOpcodeStr(Node.getOperator());
+}
 
 /// Matches overloaded operators with a specific name.
 ///

clang/include/clang/ASTMatchers/ASTMatchersInternal.h

@@ -893,6 +893,7 @@ const internal::VariadicDynCastAllOfMatcher<Stmt, CXXOperatorCallExpr>
     cxxOperatorCallExpr;
 const internal::VariadicDynCastAllOfMatcher<Stmt, CXXRewrittenBinaryOperator>
     cxxRewrittenBinaryOperator;
+const internal::VariadicDynCastAllOfMatcher<Stmt, CXXFoldExpr> cxxFoldExpr;
 const internal::VariadicDynCastAllOfMatcher<Stmt, Expr> expr;
 const internal::VariadicDynCastAllOfMatcher<Stmt, DeclRefExpr> declRefExpr;
 const internal::VariadicDynCastAllOfMatcher<Stmt, ObjCIvarRefExpr> objcIvarRefExpr;

clang/lib/ASTMatchers/ASTMatchersInternal.cpp

@@ -198,6 +198,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(cxxDependentScopeMemberExpr);
   REGISTER_MATCHER(cxxDestructorDecl);
   REGISTER_MATCHER(cxxDynamicCastExpr);
+  REGISTER_MATCHER(cxxFoldExpr);
   REGISTER_MATCHER(cxxForRangeStmt);
   REGISTER_MATCHER(cxxFunctionalCastExpr);
   REGISTER_MATCHER(cxxMemberCallExpr);
@@ -319,6 +320,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(hasExplicitSpecifier);
   REGISTER_MATCHER(hasExternalFormalLinkage);
   REGISTER_MATCHER(hasFalseExpression);
+  REGISTER_MATCHER(hasFoldInit);
   REGISTER_MATCHER(hasGlobalStorage);
   REGISTER_MATCHER(hasImplicitDestinationType);
   REGISTER_MATCHER(hasInClassInitializer);
@@ -344,6 +346,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(hasOverloadedOperatorName);
   REGISTER_MATCHER(hasParameter);
   REGISTER_MATCHER(hasParent);
+  REGISTER_MATCHER(hasPattern);
   REGISTER_MATCHER(hasPointeeLoc);
   REGISTER_MATCHER(hasQualifier);
   REGISTER_MATCHER(hasRHS);
@@ -404,6 +407,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(isAssignmentOperator);
   REGISTER_MATCHER(isAtPosition);
   REGISTER_MATCHER(isBaseInitializer);
+  REGISTER_MATCHER(isBinaryFold);
   REGISTER_MATCHER(isBitField);
   REGISTER_MATCHER(isCatchAll);
   REGISTER_MATCHER(isClass);
@@ -447,6 +451,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(isInteger);
   REGISTER_MATCHER(isIntegral);
   REGISTER_MATCHER(isLambda);
+  REGISTER_MATCHER(isLeftFold);
   REGISTER_MATCHER(isListInitialization);
   REGISTER_MATCHER(isMain);
   REGISTER_MATCHER(isMemberInitializer);
@@ -460,6 +465,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(isProtected);
   REGISTER_MATCHER(isPublic);
   REGISTER_MATCHER(isPure);
+  REGISTER_MATCHER(isRightFold);
   REGISTER_MATCHER(isScoped);
   REGISTER_MATCHER(isSharedKind);
   REGISTER_MATCHER(isSignedInteger);
@@ -469,6 +475,7 @@ RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(isStruct);
   REGISTER_MATCHER(isTemplateInstantiation);
   REGISTER_MATCHER(isTypeDependent);
+  REGISTER_MATCHER(isUnaryFold);
   REGISTER_MATCHER(isUnion);
   REGISTER_MATCHER(isUnsignedInteger);
   REGISTER_MATCHER(isUserProvided);