From d1dd9cd60a7167bc6e2f34877660e747e5b92842 Mon Sep 17 00:00:00 2001
From: Abseil Team <absl-team@google.com>
Date: Tue, 2 Apr 2024 07:41:09 -0700
Subject: Add internal traits to absl::StatusOr for lifetimebound detection

This helps compilers that understand `ABSL_ATTRIBUTE_LIFETIME_BOUND` flag constructs such as
`absl::StatusOr<std::string_view> str = std::string(...)`
as error-prone.

PiperOrigin-RevId: 621169918
Change-Id: Id621f63b9da4dc72eb4bd42c62d88bcc15a05243
---
 absl/status/internal/statusor_internal.h |  35 ++++++----
 absl/status/statusor.h                   | 108 ++++++++++++++++++++++++-------
 2 files changed, 104 insertions(+), 39 deletions(-)

(limited to 'absl/status')

diff --git a/absl/status/internal/statusor_internal.h b/absl/status/internal/statusor_internal.h
index 1afd3179..414aa300 100644
--- a/absl/status/internal/statusor_internal.h
+++ b/absl/status/internal/statusor_internal.h
@@ -123,13 +123,15 @@ using IsForwardingAssignmentValid = absl::disjunction<
         std::is_same<absl::in_place_t, absl::remove_cvref_t<U>>,
         IsForwardingAssignmentAmbiguous<T, U>>>>;
 
-template <bool Explicit, typename T>
-using NegationIf = std::conditional_t<Explicit, absl::negation<T>, T>;
+template <bool Value, typename T>
+using Equality = std::conditional_t<Value, T, absl::negation<T>>;
 
-template <typename T, typename U, bool Explicit>
+template <bool Explicit, typename T, typename U, bool Lifetimebound>
 using IsConstructionValid = absl::conjunction<
+    Equality<Lifetimebound,
+             type_traits_internal::IsLifetimeBoundAssignment<T, U>>,
     IsDirectInitializationValid<T, U&&>, std::is_constructible<T, U&&>,
-    NegationIf<Explicit, std::is_convertible<U&&, T>>,
+    Equality<!Explicit, std::is_convertible<U&&, T>>,
     absl::disjunction<
         std::is_same<T, absl::remove_cvref_t<U>>,
         absl::conjunction<
@@ -140,8 +142,10 @@ using IsConstructionValid = absl::conjunction<
             absl::negation<
                 internal_statusor::HasConversionOperatorToStatusOr<T, U&&>>>>>;
 
-template <typename T, typename U>
+template <typename T, typename U, bool Lifetimebound>
 using IsAssignmentValid = absl::conjunction<
+    Equality<Lifetimebound,
+             type_traits_internal::IsLifetimeBoundAssignment<T, U>>,
     std::is_constructible<T, U&&>, std::is_assignable<T&, U&&>,
     absl::disjunction<
         std::is_same<T, absl::remove_cvref_t<U>>,
@@ -150,27 +154,30 @@ using IsAssignmentValid = absl::conjunction<
             absl::negation<HasConversionOperatorToStatusOr<T, U&&>>>>,
     IsForwardingAssignmentValid<T, U&&>>;
 
-template <typename T, typename U, bool Explicit>
+template <bool Explicit, typename T, typename U>
 using IsConstructionFromStatusValid = absl::conjunction<
     absl::negation<std::is_same<absl::StatusOr<T>, absl::remove_cvref_t<U>>>,
     absl::negation<std::is_same<T, absl::remove_cvref_t<U>>>,
     absl::negation<std::is_same<absl::in_place_t, absl::remove_cvref_t<U>>>,
-    NegationIf<Explicit, std::is_convertible<U, absl::Status>>,
+    Equality<!Explicit, std::is_convertible<U, absl::Status>>,
     std::is_constructible<absl::Status, U>,
     absl::negation<HasConversionOperatorToStatusOr<T, U>>>;
 
-template <typename T, typename U>
-using IsStatusAssignmentValid = IsConstructionFromStatusValid<T, U, false>;
-
-template <typename T, typename U, typename UQ, bool Explicit>
+template <bool Explicit, typename T, typename U, bool Lifetimebound,
+          typename UQ>
 using IsConstructionFromStatusOrValid = absl::conjunction<
-    absl::negation<std::is_same<T, U>>, std::is_constructible<T, UQ>,
-    NegationIf<Explicit, std::is_convertible<UQ, T>>,
+    absl::negation<std::is_same<T, U>>,
+    Equality<Lifetimebound,
+             type_traits_internal::IsLifetimeBoundAssignment<T, U>>,
+    std::is_constructible<T, UQ>,
+    Equality<!Explicit, std::is_convertible<UQ, T>>,
     absl::negation<IsConstructibleOrConvertibleFromStatusOr<T, U>>>;
 
-template <typename T, typename U>
+template <typename T, typename U, bool Lifetimebound>
 using IsStatusOrAssignmentValid = absl::conjunction<
     absl::negation<std::is_same<T, absl::remove_cvref_t<U>>>,
+    Equality<Lifetimebound,
+             type_traits_internal::IsLifetimeBoundAssignment<T, U>>,
     std::is_constructible<T, U>, std::is_assignable<T, U>,
     absl::negation<IsConstructibleOrConvertibleOrAssignableFromStatusOr<
         T, absl::remove_cvref_t<U>>>>;
diff --git a/absl/status/statusor.h b/absl/status/statusor.h
index 0ed986dc..b1da45e6 100644
--- a/absl/status/statusor.h
+++ b/absl/status/statusor.h
@@ -238,29 +238,53 @@ class StatusOr : private internal_statusor::StatusOrData<T>,
   // underlying constructor.)
   template <typename U, absl::enable_if_t<
                             internal_statusor::IsConstructionFromStatusOrValid<
-                                T, U, const U&, false>::value,
+                                false, T, U, false, const U&>::value,
                             int> = 0>
   StatusOr(const StatusOr<U>& other)  // NOLINT
       : Base(static_cast<const typename StatusOr<U>::Base&>(other)) {}
   template <typename U, absl::enable_if_t<
                             internal_statusor::IsConstructionFromStatusOrValid<
-                                T, U, const U&, true>::value,
+                                false, T, U, true, const U&>::value,
+                            int> = 0>
+  StatusOr(const StatusOr<U>& other ABSL_ATTRIBUTE_LIFETIME_BOUND)  // NOLINT
+      : Base(static_cast<const typename StatusOr<U>::Base&>(other)) {}
+  template <typename U, absl::enable_if_t<
+                            internal_statusor::IsConstructionFromStatusOrValid<
+                                true, T, U, false, const U&>::value,
                             int> = 0>
   explicit StatusOr(const StatusOr<U>& other)
       : Base(static_cast<const typename StatusOr<U>::Base&>(other)) {}
+  template <typename U, absl::enable_if_t<
+                            internal_statusor::IsConstructionFromStatusOrValid<
+                                true, T, U, true, const U&>::value,
+                            int> = 0>
+  explicit StatusOr(const StatusOr<U>& other ABSL_ATTRIBUTE_LIFETIME_BOUND)
+      : Base(static_cast<const typename StatusOr<U>::Base&>(other)) {}
 
   template <typename U, absl::enable_if_t<
                             internal_statusor::IsConstructionFromStatusOrValid<
-                                T, U, U&&, false>::value,
+                                false, T, U, false, U&&>::value,
                             int> = 0>
   StatusOr(StatusOr<U>&& other)  // NOLINT
       : Base(static_cast<typename StatusOr<U>::Base&&>(other)) {}
   template <typename U, absl::enable_if_t<
                             internal_statusor::IsConstructionFromStatusOrValid<
-                                T, U, U&&, true>::value,
+                                false, T, U, true, U&&>::value,
+                            int> = 0>
+  StatusOr(StatusOr<U>&& other ABSL_ATTRIBUTE_LIFETIME_BOUND)  // NOLINT
+      : Base(static_cast<typename StatusOr<U>::Base&&>(other)) {}
+  template <typename U, absl::enable_if_t<
+                            internal_statusor::IsConstructionFromStatusOrValid<
+                                true, T, U, false, U&&>::value,
                             int> = 0>
   explicit StatusOr(StatusOr<U>&& other)
       : Base(static_cast<typename StatusOr<U>::Base&&>(other)) {}
+  template <typename U, absl::enable_if_t<
+                            internal_statusor::IsConstructionFromStatusOrValid<
+                                true, T, U, true, U&&>::value,
+                            int> = 0>
+  explicit StatusOr(StatusOr<U>&& other ABSL_ATTRIBUTE_LIFETIME_BOUND)
+      : Base(static_cast<typename StatusOr<U>::Base&&>(other)) {}
 
   // Converting Assignment Operators
 
@@ -283,20 +307,36 @@ class StatusOr : private internal_statusor::StatusOrData<T>,
   // assigned from `StatusOr<U>`.
   template <typename U,
             absl::enable_if_t<internal_statusor::IsStatusOrAssignmentValid<
-                                  T, const U&>::value,
+                                  T, const U&, false>::value,
                               int> = 0>
   StatusOr& operator=(const StatusOr<U>& other) {
     this->Assign(other);
     return *this;
   }
-  template <
-      typename U,
-      absl::enable_if_t<
-          internal_statusor::IsStatusOrAssignmentValid<T, U&&>::value, int> = 0>
+  template <typename U,
+            absl::enable_if_t<internal_statusor::IsStatusOrAssignmentValid<
+                                  T, const U&, true>::value,
+                              int> = 0>
+  StatusOr& operator=(const StatusOr<U>& other ABSL_ATTRIBUTE_LIFETIME_BOUND) {
+    this->Assign(other);
+    return *this;
+  }
+  template <typename U,
+            absl::enable_if_t<internal_statusor::IsStatusOrAssignmentValid<
+                                  T, U&&, false>::value,
+                              int> = 0>
   StatusOr& operator=(StatusOr<U>&& other) {
     this->Assign(std::move(other));
     return *this;
   }
+  template <typename U,
+            absl::enable_if_t<internal_statusor::IsStatusOrAssignmentValid<
+                                  T, U&&, true>::value,
+                              int> = 0>
+  StatusOr& operator=(StatusOr<U>&& other ABSL_ATTRIBUTE_LIFETIME_BOUND) {
+    this->Assign(std::move(other));
+    return *this;
+  }
 
   // Constructs a new `absl::StatusOr<T>` with a non-ok status. After calling
   // this constructor, `this->ok()` will be `false` and calls to `value()` will
@@ -311,20 +351,19 @@ class StatusOr : private internal_statusor::StatusOrData<T>,
   // of passing absl::StatusCode::kInternal as a fallback.
   template <typename U = absl::Status,
             absl::enable_if_t<internal_statusor::IsConstructionFromStatusValid<
-                                  T, U, false>::value,
+                                  false, T, U>::value,
                               int> = 0>
   StatusOr(U&& v) : Base(std::forward<U>(v)) {}
 
   template <typename U = absl::Status,
             absl::enable_if_t<internal_statusor::IsConstructionFromStatusValid<
-                                  T, U, true>::value,
+                                  true, T, U>::value,
                               int> = 0>
   explicit StatusOr(U&& v) : Base(std::forward<U>(v)) {}
-
-  template <
-      typename U = absl::Status,
-      absl::enable_if_t<internal_statusor::IsStatusAssignmentValid<T, U>::value,
-                        int> = 0>
+  template <typename U = absl::Status,
+            absl::enable_if_t<internal_statusor::IsConstructionFromStatusValid<
+                                  false, T, U>::value,
+                              int> = 0>
   StatusOr& operator=(U&& v) {
     this->AssignStatus(std::forward<U>(v));
     return *this;
@@ -347,12 +386,21 @@ class StatusOr : private internal_statusor::StatusOrData<T>,
   //    StatusOr<bool> s2 = false;  // s2.ok() && *s2 == false
   //    s1 = s2;  // ambiguous, `s1 = *s2` or `s1 = bool(s2)`?
   template <typename U = T,
-            typename = typename std::enable_if<
-                internal_statusor::IsAssignmentValid<T, U>::value>::type>
+            typename std::enable_if<
+                internal_statusor::IsAssignmentValid<T, U, false>::value,
+                int>::type = 0>
   StatusOr& operator=(U&& v) {
     this->Assign(std::forward<U>(v));
     return *this;
   }
+  template <typename U = T,
+            typename std::enable_if<
+                internal_statusor::IsAssignmentValid<T, U, true>::value,
+                int>::type = 0>
+  StatusOr& operator=(U&& v ABSL_ATTRIBUTE_LIFETIME_BOUND) {
+    this->Assign(std::forward<U>(v));
+    return *this;
+  }
 
   // Constructs the inner value `T` in-place using the provided args, using the
   // `T(args...)` constructor.
@@ -370,19 +418,29 @@ class StatusOr : private internal_statusor::StatusOrData<T>,
   // ambiguity, this constructor is disabled if `U` is a `StatusOr<J>`, where
   // `J` is convertible to `T`.
   template <typename U = T,
-            absl::enable_if_t<
-                absl::conjunction<internal_statusor::IsConstructionValid<
-                    T, U, false> >::value,
-                int> = 0>
+            absl::enable_if_t<internal_statusor::IsConstructionValid<
+                                  false, T, U, false>::value,
+                              int> = 0>
   StatusOr(U&& u)  // NOLINT
       : StatusOr(absl::in_place, std::forward<U>(u)) {}
+  template <typename U = T,
+            absl::enable_if_t<internal_statusor::IsConstructionValid<
+                                  false, T, U, true>::value,
+                              int> = 0>
+  StatusOr(U&& u ABSL_ATTRIBUTE_LIFETIME_BOUND)  // NOLINT
+      : StatusOr(absl::in_place, std::forward<U>(u)) {}
 
+  template <typename U = T,
+            absl::enable_if_t<internal_statusor::IsConstructionValid<
+                                  true, T, U, false>::value,
+                              int> = 0>
+  explicit StatusOr(U&& u)  // NOLINT
+      : StatusOr(absl::in_place, std::forward<U>(u)) {}
   template <typename U = T,
             absl::enable_if_t<
-                absl::conjunction<
-                    internal_statusor::IsConstructionValid<T, U, true> >::value,
+                internal_statusor::IsConstructionValid<true, T, U, true>::value,
                 int> = 0>
-  explicit StatusOr(U&& u)  // NOLINT
+  explicit StatusOr(U&& u ABSL_ATTRIBUTE_LIFETIME_BOUND)  // NOLINT
       : StatusOr(absl::in_place, std::forward<U>(u)) {}
 
   // StatusOr<T>::ok()
-- 
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