[clang] [Clang][Sema] Properly get captured 'this' pointer in lambdas with an explicit object parameter in constant evaluator (PR #81102)

[via cfe-commits]

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@@ -8480,6 +8480,54 @@ class LValueExprEvaluator
 };
 } // end anonymous namespace
 
+/// Get an lvalue to a field of a lambda's closure type.
+static bool GetLambdaCaptureAsLValue(EvalInfo &Info, const Expr *E,
+                                     LValue &Result, const CXXMethodDecl *MD,
+                                     const FieldDecl *FD,
+                                     bool LValueToRValueConversion) {
+  // Static lambda function call operators can't have captures. We already
+  // diagnosed this, so bail out here.
+  if (MD->isStatic()) {
+    assert(Info.CurrentCall->This == nullptr &&
+           "This should not be set for a static call operator");
+    return false;
+  }
+
+  // Start with 'Result' referring to the complete closure object...
+  if (MD->isExplicitObjectMemberFunction()) {
+    // Self may be passed by reference or by value.
+    auto *Self = MD->getParamDecl(0);
+    if (Self->getType()->isReferenceType()) {
+      APValue *RefValue = Info.getParamSlot(Info.CurrentCall->Arguments, Self);
+      Result.setFrom(Info.Ctx, *RefValue);
+    } else {
+      auto *VD = Info.CurrentCall->Arguments.getOrigParam(Self);
+      auto *Frame =
+          Info.getCallFrameAndDepth(Info.CurrentCall->Arguments.CallIndex)
+              .first;
+      auto Version = Info.CurrentCall->Arguments.Version;
+      Result.set({VD, Frame->Index, Version});
+    }
+  } else
+    Result = *Info.CurrentCall->This;
+
+  // ... then update it to refer to the field of the closure object
+  // that represents the capture.
+  if (!HandleLValueMember(Info, E, Result, FD))
+    return false;
+
+  // And if the field is of reference type (or if we captured '*this' by
+  // reference if this is a lambda), update 'Result' to refer to what
+  // the field refers to.
----------------
cor3ntin wrote:

```suggestion
  // And if the field is of reference type (or if we captured '*this' by
  // reference), update 'Result' to refer to what
  // the field refers to.
```

https://github.com/llvm/llvm-project/pull/81102