[clang] Crash when referencing capture in static lambda (#74661)

The constant evaluator could try to reference a lambda capture in a
static lambda call operator. Static lambdas can't have captures, so we
simply abort. Either the lambda needs to be made non-static, or the
capture (and reference to it) need to be removed.

Fixes: #74608

Author: puremourning

clang/docs/ReleaseNotes.rst

@@ -870,6 +870,10 @@ Miscellaneous Clang Crashes Fixed
   `Issue 41302 <https://github.com/llvm/llvm-project/issues/41302>`_
 - Fixed a crash when ``-ast-dump=json`` was used for code using class
   template deduction guides.
+- Fixed a crash when a lambda marked as ``static`` referenced a captured
+  variable in an expression.
+  `Issue 74608 <https://github.com/llvm/llvm-project/issues/74608>`_
+
 
 OpenACC Specific Changes
 ------------------------

clang/lib/AST/ExprConstant.cpp

@@ -8514,14 +8514,24 @@ bool LValueExprEvaluator::VisitVarDecl(const Expr *E, const VarDecl *VD) {
       return false;
 
     if (auto *FD = Info.CurrentCall->LambdaCaptureFields.lookup(VD)) {
+      const auto *MD = cast<CXXMethodDecl>(Info.CurrentCall->Callee);
+
+      // 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 (auto *MD = cast<CXXMethodDecl>(Info.CurrentCall->Callee);
-          MD->isExplicitObjectMemberFunction()) {
+      if (MD->isExplicitObjectMemberFunction()) {
         APValue *RefValue =
             Info.getParamSlot(Info.CurrentCall->Arguments, MD->getParamDecl(0));
         Result.setFrom(Info.Ctx, *RefValue);
       } 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))

clang/test/Parser/cxx2b-lambdas.cpp

@@ -66,3 +66,15 @@ void static_captures() {
     }
   };
 }
+
+constexpr auto static_capture_constexpr() {
+  char n = 'n';
+  return [n] static { return n; }(); // expected-error {{a static lambda cannot have any captures}}
+}
+static_assert(static_capture_constexpr()); // expected-error {{static assertion expression is not an integral constant expression}}
+
+constexpr auto capture_constexpr() {
+  char n = 'n';
+  return [n] { return n; }();
+}
+static_assert(capture_constexpr());