[clang][dataflow] Handle this-capturing lambdas in field initializers. (#99519)

We previously would assume these lambdas appeared inside a method
definition and end up crashing.

Author: bazuzi

clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp

@@ -524,12 +524,21 @@ void Environment::initialize() {
           assert(VarDecl != nullptr);
           setStorageLocation(*VarDecl, createObject(*VarDecl, nullptr));
         } else if (Capture.capturesThis()) {
-          const auto *SurroundingMethodDecl =
-              cast<CXXMethodDecl>(InitialTargetFunc->getNonClosureAncestor());
-          QualType ThisPointeeType =
-              SurroundingMethodDecl->getFunctionObjectParameterType();
-          setThisPointeeStorageLocation(
-              cast<RecordStorageLocation>(createObject(ThisPointeeType)));
+          if (auto *Ancestor = InitialTargetFunc->getNonClosureAncestor()) {
+            const auto *SurroundingMethodDecl = cast<CXXMethodDecl>(Ancestor);
+            QualType ThisPointeeType =
+                SurroundingMethodDecl->getFunctionObjectParameterType();
+            setThisPointeeStorageLocation(
+                cast<RecordStorageLocation>(createObject(ThisPointeeType)));
+          } else if (auto *FieldBeingInitialized =
+                         dyn_cast<FieldDecl>(Parent->getLambdaContextDecl())) {
+            // This is in a field initializer, rather than a method.
+            setThisPointeeStorageLocation(
+                cast<RecordStorageLocation>(createObject(QualType(
+                    FieldBeingInitialized->getParent()->getTypeForDecl(), 0))));
+          } else {
+            assert(false && "Unexpected this-capturing lambda context.");
+          }
         }
       }
     } else if (MethodDecl->isImplicitObjectMemberFunction()) {

clang/unittests/Analysis/FlowSensitive/DataflowEnvironmentTest.cpp

@@ -473,4 +473,32 @@ TEST_F(EnvironmentTest, Stmt) {
   Env.getResultObjectLocation(*Init);
 }
 
+// This is a crash repro.
+TEST_F(EnvironmentTest, LambdaCapturingThisInFieldInitializer) {
+  using namespace ast_matchers;
+  std::string Code = R"cc(
+      struct S {
+        int f{[this]() { return 1; }()};
+      };
+    )cc";
+
+  auto Unit =
+      tooling::buildASTFromCodeWithArgs(Code, {"-fsyntax-only", "-std=c++11"});
+  auto &Context = Unit->getASTContext();
+
+  ASSERT_EQ(Context.getDiagnostics().getClient()->getNumErrors(), 0U);
+
+  auto *LambdaCallOperator = selectFirst<CXXMethodDecl>(
+      "method", match(cxxMethodDecl(hasName("operator()"),
+                                    ofClass(cxxRecordDecl(isLambda())))
+                          .bind("method"),
+                      Context));
+
+  Environment Env(DAContext, *LambdaCallOperator);
+  // Don't crash when initializing.
+  Env.initialize();
+  // And initialize the captured `this` pointee.
+  ASSERT_NE(nullptr, Env.getThisPointeeStorageLocation());
+}
+
 } // namespace