[clang][dataflow] Add a test for a struct that is directly self-referential through a reference.

[mboehme]

Summary

The ongoing migration to strict handling of value
categories (see https://discourse.llvm.org/t/70086) will change the way we
handle fields of reference type, and I want to put a test in place that makes
sure we continue to handle this special case correctly.

Depends On D154420

[mboehme]

Actually make the test pass. It was missing an indirection.

No idea how I missed this on the initial upload...

[mboehme]

Pre-merge failure looks unrelated

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

runDataflow(
 
         const auto *BazPtrVal =
             cast<PointerValue>(BarPointeeVal->getChild(*BazPtrDecl));
         const StorageLocation &BazPtrPointeeLoc = BazPtrVal->getPointeeLoc();
         EXPECT_THAT(Env.getValue(BazPtrPointeeLoc), NotNull());
       });
 }
 
+TEST(TransferTest, DirectlySelfReferentialReference) {
+  std::string Code = R"(
+    struct target {
+      target() {
+        (void)0;
+        // [[p]]
+      }
+      target &self = *this;
+    };
+  )";
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+        const ValueDecl *SelfDecl = findValueDecl(ASTCtx, "self");
+
+        auto *ThisLoc = Env.getThisPointeeStorageLocation();
+        auto *RefVal =
+            cast<ReferenceValue>(Env.getValue(ThisLoc->getChild(*SelfDecl)));
+        ASSERT_EQ(&RefVal->getReferentLoc(), ThisLoc);
+      });
+}
+
 TEST(TransferTest, MultipleVarsDecl) {
   std::string Code = R"(
     void target() {
       int Foo, Bar;
       (void)0;
       // [[p]]
     }
   )";