[SyntaxTree] Ignore leaf implicit `CXXConstructExpr`

[eduucaldas]

Summary

This is builds upon:
https://reviews.llvm.org/D86699

[eduucaldas]

Rebase

[gribozavr2]

clang/unittests/Tooling/Syntax/BuildTreeTest.cpp

552

Do we have tests for calling constructors with arguments?

n::S s3(1, 2, 3);
n::S s3{1, 2, 3};

If not, please add them.

[eduucaldas]

.

[eduucaldas]

.

[eduucaldas]

clang/unittests/Tooling/Syntax/BuildTreeTest.cpp

552

We have. I improved their coverage in the parent patch

[eduucaldas]

Add comments

[gribozavr2]

clang/lib/Tooling/Syntax/BuildTree.cpp

1136

1137

I don't quite understand which test is checking the CXXDefaultArgExpr case -- could you help me?

[eduucaldas]

answer comments

clang/lib/Tooling/Syntax/BuildTree.cpp

1137

CXXDefaultArgExpr is in another patch. Although I discovered while working on this it is as linked to Constructors as it is linked to function calls. As such I decided to add that in a separate patch

[gribozavr2]

clang/lib/Tooling/Syntax/BuildTree.cpp

1137

OK, added a comment in that review.

clang/lib/Tooling/Syntax/BuildTree.cpp

bool WalkUpFromCallExpr(CallExpr *S) {
 
     Builder.markChildToken(S->getRParenLoc(), syntax::NodeRole::CloseParen);
 
     Builder.foldNode(Builder.getRange(S->getSourceRange()),
                      new (allocator()) syntax::CallExpression, S);
     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
     // operator and treat it as a simple token. Do that by traversing
     // arguments instead of children.
     for (auto *child : S->arguments()) {
       // A postfix unary operator is declared as taking two operands. The
       // second operand is used to distinguish from its prefix counterpart. In

clang/unittests/Tooling/Syntax/BuildTreeTest.cpp

if (!GetParam().isCXX()) {
     return;
   }
   EXPECT_TRUE(treeDumpEqualOnAnnotations(
       R"cpp(
 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]];
 }
 )cpp",
       {R"txt(
 SimpleDeclaration
 |-NestedNameSpecifier
 | |-'::' ListDelimiter
 | |-IdentifierNameSpecifier ListElement
 | | `-'n'
 | `-'::' ListDelimiter
 |-'S'
 `-SimpleDeclarator Declarator
-  `-UnknownExpression
-    `-'s1'
 )txt",
        R"txt(
 SimpleDeclaration
 |-NestedNameSpecifier
 | |-IdentifierNameSpecifier ListElement
 | | `-'n'
 | `-'::' ListDelimiter
 |-'S'
 `-SimpleDeclarator Declarator
-  `-UnknownExpression
-    `-'s2'
 )txt"}));
 }
 
 TEST_P(SyntaxTreeTest, QualifiedId_TemplateSpecifier) {
   if (!GetParam().isCXX()) {
     return;
   }
   EXPECT_TRUE(treeDumpEqualOnAnnotations(

 | | |-'template'
 | | |-'ST'
 | | |-'<'
 | | |-'int'
 | | `-'>'
 | `-'::' ListDelimiter
 |-'S'
 `-SimpleDeclarator Declarator
-  `-UnknownExpression
-    `-'s1'
 )txt",
        R"txt(
 SimpleDeclaration
 |-NestedNameSpecifier
 | |-'::' ListDelimiter
 | |-SimpleTemplateNameSpecifier ListElement
 | | |-'ST'
 | | |-'<'
 | | |-'int'
 | | `-'>'
 | `-'::' ListDelimiter
 |-'S'
 `-SimpleDeclarator Declarator
-  `-UnknownExpression
-    `-'s2'
 )txt"}));
 }
 
 TEST_P(SyntaxTreeTest, QualifiedId_DecltypeSpecifier) {
   if (!GetParam().isCXX11OrLater()) {
     return;
   }
   EXPECT_TRUE(treeDumpEqualOnAnnotations(