[clang] [LifetimeSafety] Warn on implicit this lifetimebound violations (PR #196926)

[Gábor Horváth via cfe-commits]

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@@ -72,21 +72,29 @@ getLifetimeBoundAttrFromFunctionType(const TypeSourceInfo &TSI) {
   return nullptr;
 }
 
-bool implicitObjectParamIsLifetimeBound(const FunctionDecl *FD) {
+const LifetimeBoundAttr *
+getImplicitObjectParamLifetimeBoundAttr(const FunctionDecl *FD) {
   FD = getDeclWithMergedLifetimeBoundAttrs(FD);
   // Attribute merging doesn't work well with attributes on function types (like
   // 'this' param). We need to check all redeclarations.
-  auto CheckRedecls = [](const FunctionDecl *F) {
-    return llvm::any_of(F->redecls(), [](const FunctionDecl *Redecl) {
-      const TypeSourceInfo *TSI = Redecl->getTypeSourceInfo();
-      return TSI && getLifetimeBoundAttrFromFunctionType(*TSI);
-    });
+  auto CheckRedecls = [](const FunctionDecl *F) -> const LifetimeBoundAttr * {
+    for (const FunctionDecl *Redecl : F->redecls()) {
+      if (const TypeSourceInfo *TSI = Redecl->getTypeSourceInfo())
+        if (const auto *Attr = getLifetimeBoundAttrFromFunctionType(*TSI))
+          return Attr;
+    }
+    return nullptr;
   };
 
-  if (CheckRedecls(FD))
-    return true;
-  if (const FunctionDecl *Pattern = FD->getTemplateInstantiationPattern();
-      Pattern && CheckRedecls(Pattern))
+  if (const auto *Attr = CheckRedecls(FD))
+    return Attr;
+  if (const FunctionDecl *Pattern = FD->getTemplateInstantiationPattern())
+    return CheckRedecls(Pattern);
+  return nullptr;
+}
+
+bool implicitObjectParamIsLifetimeBound(const FunctionDecl *FD) {
+  if (getImplicitObjectParamLifetimeBoundAttr(FD))
     return true;
   return isNormalAssignmentOperator(FD);
----------------
Xazax-hun wrote:

We do not actually do the verification for assignment operators. I think this is fine, as this was not explicitly spelled by the user. But I wonder if we should have a potentially separate warning when an assignment operator returns an unexpected loan. This could be a separate PR. 

https://github.com/llvm/llvm-project/pull/196926