[clang] Update `ignoringElidableConstructorCall` matcher to ignore `ExprWithCleanups`.

Summary:
The `ExprWithCleanups` node is added to the AST along with the elidable
CXXConstructExpr.  If it is the outermost node of the node being matched, ignore
it as well.

Reviewers: gribozavr

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D65944

llvm-svn: 368319

clang/docs/LibASTMatchersReference.html

@@ -5805,14 +5805,15 @@ Example matches x (matcher = expr(hasType(cxxRecordDecl(hasName("X")))))
 
 <tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1Expr.html">Expr</a>&gt;</td><td class="name" onclick="toggle('ignoringElidableConstructorCall0')"><a name="ignoringElidableConstructorCall0Anchor">ignoringElidableConstructorCall</a></td><td>ast_matchers::Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1Expr.html">Expr</a>&gt; InnerMatcher</td></tr>
 <tr><td colspan="4" class="doc" id="ignoringElidableConstructorCall0"><pre>Matches expressions that match InnerMatcher that are possibly wrapped in an
-elidable constructor.
+elidable constructor and other corresponding bookkeeping nodes.
 
-In C++17 copy elidable constructors are no longer being
-generated in the AST as it is not permitted by the standard. They are
-however part of the AST in C++14 and earlier. Therefore, to write a matcher
-that works in all language modes, the matcher has to skip elidable
-constructor AST nodes if they appear in the AST. This matcher can be used to
-skip those elidable constructors.
+In C++17, elidable copy constructors are no longer being generated in the
+AST as it is not permitted by the standard. They are, however, part of the
+AST in C++14 and earlier. So, a matcher must abstract over these differences
+to work in all language modes. This matcher skips elidable constructor-call
+AST nodes, `ExprWithCleanups` nodes wrapping elidable constructor-calls and
+various implicit nodes inside the constructor calls, all of which will not
+appear in the C++17 AST.
 
 Given
 
@@ -5822,10 +5823,8 @@ void f() {
   H D = G();
 }
 
-``varDecl(hasInitializer(any(
-      ignoringElidableConstructorCall(callExpr()),
-      exprWithCleanups(ignoringElidableConstructorCall(callExpr()))))``
-matches ``H D = G()``
+``varDecl(hasInitializer(ignoringElidableConstructorCall(callExpr())))``
+matches ``H D = G()`` in C++11 through C++17 (and beyond).
 </pre></td></tr>
 
 

clang/include/clang/ASTMatchers/ASTMatchers.h

@@ -6533,14 +6533,15 @@ AST_MATCHER(FunctionDecl, hasTrailingReturn) {
 }
 
 /// Matches expressions that match InnerMatcher that are possibly wrapped in an
-/// elidable constructor.
+/// elidable constructor and other corresponding bookkeeping nodes.
 ///
-/// In C++17 copy elidable constructors are no longer being
-/// generated in the AST as it is not permitted by the standard. They are
-/// however part of the AST in C++14 and earlier. Therefore, to write a matcher
-/// that works in all language modes, the matcher has to skip elidable
-/// constructor AST nodes if they appear in the AST. This matcher can be used to
-/// skip those elidable constructors.
+/// In C++17, elidable copy constructors are no longer being generated in the
+/// AST as it is not permitted by the standard. They are, however, part of the
+/// AST in C++14 and earlier. So, a matcher must abstract over these differences
+/// to work in all language modes. This matcher skips elidable constructor-call
+/// AST nodes, `ExprWithCleanups` nodes wrapping elidable constructor-calls and
+/// various implicit nodes inside the constructor calls, all of which will not
+/// appear in the C++17 AST.
 ///
 /// Given
 ///
@@ -6552,13 +6553,20 @@ AST_MATCHER(FunctionDecl, hasTrailingReturn) {
 /// }
 /// \endcode
 ///
-/// ``varDecl(hasInitializer(any(
-///       ignoringElidableConstructorCall(callExpr()),
-///       exprWithCleanups(ignoringElidableConstructorCall(callExpr()))))``
-/// matches ``H D = G()``
+/// ``varDecl(hasInitializer(ignoringElidableConstructorCall(callExpr())))``
+/// matches ``H D = G()`` in C++11 through C++17 (and beyond).
 AST_MATCHER_P(Expr, ignoringElidableConstructorCall,
               ast_matchers::internal::Matcher<Expr>, InnerMatcher) {
-  if (const auto *CtorExpr = dyn_cast<CXXConstructExpr>(&Node)) {
+  // E tracks the node that we are examining.
+  const Expr *E = &Node;
+  // If present, remove an outer `ExprWithCleanups` corresponding to the
+  // underlying `CXXConstructExpr`. This check won't cover all cases of added
+  // `ExprWithCleanups` corresponding to `CXXConstructExpr` nodes (because the
+  // EWC is placed on the outermost node of the expression, which this may not
+  // be), but, it still improves the coverage of this matcher.
+  if (const auto *CleanupsExpr = dyn_cast<ExprWithCleanups>(&Node))
+    E = CleanupsExpr->getSubExpr();
+  if (const auto *CtorExpr = dyn_cast<CXXConstructExpr>(E)) {
     if (CtorExpr->isElidable()) {
       if (const auto *MaterializeTemp =
               dyn_cast<MaterializeTemporaryExpr>(CtorExpr->getArg(0))) {

clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp

@@ -671,6 +671,23 @@ TEST(Matcher, IgnoresElidableDoesNotPreventMatches) {
                       LanguageMode::Cxx11OrLater));
 }
 
+TEST(Matcher, IgnoresElidableInVarInit) {
+  auto matcher =
+      varDecl(hasInitializer(ignoringElidableConstructorCall(callExpr())));
+  EXPECT_TRUE(matches("struct H {};"
+                      "H G();"
+                      "void f(H D = G()) {"
+                      "  return;"
+                      "}",
+                      matcher, LanguageMode::Cxx11OrLater));
+  EXPECT_TRUE(matches("struct H {};"
+                      "H G();"
+                      "void f() {"
+                      "  H D = G();"
+                      "}",
+                      matcher, LanguageMode::Cxx11OrLater));
+}
+
 TEST(Matcher, BindTheSameNameInAlternatives) {
   StatementMatcher matcher = anyOf(
     binaryOperator(hasOperatorName("+"),