Adapt CastExpr::getSubExprAsWritten to ConstantExpr

[sberg]

I hit this with a call to getSubExprAsWriten from the LibreOffice Clang plugin, have no idea whether it can be hit from within the compiler itself. Not sure if clang/unittests/Tooling/CastExprTest.cpp is the best place to add a test for it.

[sberg]

ping

(addressed the clang-tidy nitpick)

[sberg]

ping^2

[sberg]

friendly ping

[sberg]

ping

[sberg]

ping

[sberg]

Ping; OK to submit? (I meanwhile also get this when compiling some code with plain Clang, not just with the LibreOffice Clang plugin where I saw it originally.)

clang/lib/AST/Expr.cpp

Expr *CastExpr::getSubExprAsWritten() {
   const Expr *SubExpr = nullptr;
   const CastExpr *E = this;
   do {
     SubExpr = skipImplicitTemporary(E->getSubExpr());
 
     // Conversions by constructor and conversion functions have a
     // subexpression describing the call; strip it off.
     if (E->getCastKind() == CK_ConstructorConversion)
-      SubExpr =
-        skipImplicitTemporary(cast<CXXConstructExpr>(SubExpr)->getArg(0));
+      SubExpr = skipImplicitTemporary(
+          cast<CXXConstructExpr>(SubExpr->IgnoreImplicit())->getArg(0));
     else if (E->getCastKind() == CK_UserDefinedConversion) {
       assert((isa<CXXMemberCallExpr>(SubExpr) ||
               isa<BlockExpr>(SubExpr)) &&
              "Unexpected SubExpr for CK_UserDefinedConversion.");
       if (auto *MCE = dyn_cast<CXXMemberCallExpr>(SubExpr))
         SubExpr = MCE->getImplicitObjectArgument();
     }
 

clang/unittests/Tooling/CastExprTest.cpp

Visitor.OnExplicitCast = [](ExplicitCastExpr *Expr) {
       EXPECT_TRUE(isa<DeclRefExpr>(Sub))
         << "Expected DeclRefExpr, but saw " << Sub->getStmtClassName();
     };
     Visitor.runOver("struct S1 {};\n"
                     "struct S2 { operator S1(); };\n"
                     "S1 f(S2 s) { return static_cast<S1>(s); }\n");
 }
 
+// Verify that getSubExprAsWritten looks through a ConstantExpr in a scenario
+// like
+//
+//   CXXFunctionalCastExpr functional cast to struct S <ConstructorConversion>
+//   `-ConstantExpr 'S'
+//     |-value: Struct
+//     `-CXXConstructExpr 'S' 'void (int)'
+//       `-IntegerLiteral 'int' 0
+TEST(CastExprTest, GetSubExprAsWrittenThroughConstantExpr) {
+  CastExprVisitor Visitor;
+  Visitor.OnExplicitCast = [](ExplicitCastExpr *Expr) {
+    auto Sub = Expr->getSubExprAsWritten();
+    EXPECT_TRUE(isa<IntegerLiteral>(Sub))
+        << "Expected IntegerLiteral, but saw " << Sub->getStmtClassName();
+  };
+  Visitor.runOver("struct S { consteval S(int) {} };\n"
+                  "S f() { return S(0); }\n",
+                  CastExprVisitor::Lang_CXX2a);
+}
 }