[SyntaxTree] Ignore implicit leaf `CXXConstructExpr`

Differential Revision: https://reviews.llvm.org/D86700

clang/lib/Tooling/Syntax/BuildTree.cpp

@@ -1132,6 +1132,14 @@ public:
     return true;
   }
 
+  bool WalkUpFromCXXConstructExpr(CXXConstructExpr *S) {
+    // Ignore the implicit calls to default constructors.
+    if ((S->getNumArgs() == 0 || isa<CXXDefaultArgExpr>(S->getArg(0))) &&
+        S->getParenOrBraceRange().isInvalid())
+      return true;
+    return RecursiveASTVisitor::WalkUpFromCXXConstructExpr(S);
+  }
+
   bool TraverseCXXOperatorCallExpr(CXXOperatorCallExpr *S) {
     // To construct a syntax tree of the same shape for calls to built-in and
     // user-defined operators, ignore the `DeclRefExpr` that refers to the

clang/unittests/Tooling/Syntax/BuildTreeTest.cpp

@@ -548,9 +548,6 @@ namespace n {
   struct S { };
 }
 void test() {
-  // FIXME: Remove the `UnknownExpression` wrapping `s1` and `s2`. This
-  // `UnknownExpression` comes from a leaf `CXXConstructExpr` in the
-  // ClangAST. We need to ignore leaf implicit nodes.
   [[::n::S s1]];
   [[n::S s2]];
 }
@@ -564,8 +561,7 @@ SimpleDeclaration
 | `-'::' ListDelimiter
 |-'S'
 `-SimpleDeclarator Declarator
-  `-UnknownExpression
-    `-'s1'
+  `-'s1'
 )txt",
        R"txt(
 SimpleDeclaration
@@ -575,8 +571,7 @@ SimpleDeclaration
 | `-'::' ListDelimiter
 |-'S'
 `-SimpleDeclarator Declarator
-  `-UnknownExpression
-    `-'s2'
+  `-'s2'
 )txt"}));
 }
 
@@ -608,8 +603,7 @@ SimpleDeclaration
 | `-'::' ListDelimiter
 |-'S'
 `-SimpleDeclarator Declarator
-  `-UnknownExpression
-    `-'s1'
+  `-'s1'
 )txt",
        R"txt(
 SimpleDeclaration
@@ -623,8 +617,7 @@ SimpleDeclaration
 | `-'::' ListDelimiter
 |-'S'
 `-SimpleDeclarator Declarator
-  `-UnknownExpression
-    `-'s2'
+  `-'s2'
 )txt"}));
 }