Make pdfium::span<> be based off of UnownedPtr<>.

Because we can get the lifetime check for free if we do this. This
requires adding some "constexpr/noexcept" to UnownedPtr to make the
types line up with what span.h requires.

Change-Id: I45918f8723122082036eed959f769644ab4c509f
Reviewed-on: https://pdfium-review.googlesource.com/29672
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>

3 files changed, 16 insertions, 14 deletions

diff --git a/core/fxcrt/unowned_ptr.h b/core/fxcrt/unowned_ptr.h
index b1c9c66b3e..0e3bf9e09b 100644
--- a/core/fxcrt/unowned_ptr.h
+++ b/core/fxcrt/unowned_ptr.h
@@ -40,25 +40,25 @@ namespace fxcrt {
 template <class T>
 class UnownedPtr {
  public:
-  UnownedPtr() = default;
-  UnownedPtr(const UnownedPtr& that) : UnownedPtr(that.Get()) {}
+  constexpr UnownedPtr() noexcept = default;
+  constexpr UnownedPtr(const UnownedPtr& that) noexcept = default;
 
   template <typename U>
-  explicit UnownedPtr(U* pObj) : m_pObj(pObj) {}
+  explicit constexpr UnownedPtr(U* pObj) noexcept : m_pObj(pObj) {}
 
   // Deliberately implicit to allow returning nullptrs.
   // NOLINTNEXTLINE(runtime/explicit)
-  UnownedPtr(std::nullptr_t ptr) {}
+  constexpr UnownedPtr(std::nullptr_t ptr) noexcept {}
 
   ~UnownedPtr() { ProbeForLowSeverityLifetimeIssue(); }
 
-  UnownedPtr& operator=(T* that) {
+  UnownedPtr& operator=(T* that) noexcept {
     ProbeForLowSeverityLifetimeIssue();
     m_pObj = that;
     return *this;
   }
 
-  UnownedPtr& operator=(const UnownedPtr& that) {
+  UnownedPtr& operator=(const UnownedPtr& that) noexcept {
     ProbeForLowSeverityLifetimeIssue();
     if (*this != that)
       m_pObj = that.Get();
@@ -81,7 +81,7 @@ class UnownedPtr {
     return !(*this == that);
   }
 
-  T* Get() const { return m_pObj; }
+  T* Get() const noexcept { return m_pObj; }
 
   T* Release() {
     ProbeForLowSeverityLifetimeIssue();
diff --git a/third_party/DEPS b/third_party/DEPS
index 93ca1a0bd4..392d0124c9 100644
--- a/third_party/DEPS
+++ b/third_party/DEPS
@@ -3,5 +3,6 @@ include_rules = [
   '+core/fxcrt/fx_coordinates.h',
   '+core/fxcrt/fx_memory.h',
   '+core/fxcrt/fx_system.h',
+  '+core/fxcrt/unowned_ptr.h',
   '+build',
 ]
diff --git a/third_party/base/span.h b/third_party/base/span.h
index d8d8f29e7c..034c6a35e7 100644
--- a/third_party/base/span.h
+++ b/third_party/base/span.h
@@ -13,6 +13,7 @@
 #include <type_traits>
 #include <utility>
 
+#include "core/fxcrt/unowned_ptr.h"
 #include "third_party/base/logging.h"
 
 namespace pdfium {
@@ -224,14 +225,14 @@ class span {
 
   const span last(size_t count) const {
     CHECK(count <= size_);
-    return span(data_ + (size_ - count), count);
+    return span(data_.Get() + (size_ - count), count);
   }
 
   const span subspan(size_t pos, size_t count = -1) const {
     const auto npos = static_cast<size_t>(-1);
     CHECK(pos <= size_);
     CHECK(count == npos || count <= size_ - pos);
-    return span(data_ + pos, count == npos ? size_ - pos : count);
+    return span(data_.Get() + pos, count == npos ? size_ - pos : count);
   }
 
   // [span.obs], span observers
@@ -241,13 +242,13 @@ class span {
   // [span.elem], span element access
   const T& operator[](size_t index) const noexcept {
     CHECK(index < size_);
-    return data_[index];
+    return data_.Get()[index];
   }
-  constexpr T* data() const noexcept { return data_; }
+  constexpr T* data() const noexcept { return data_.Get(); }
 
   // [span.iter], span iterator support
-  constexpr iterator begin() const noexcept { return data_; }
-  constexpr iterator end() const noexcept { return data_ + size_; }
+  constexpr iterator begin() const noexcept { return data_.Get(); }
+  constexpr iterator end() const noexcept { return data_.Get() + size_; }
 
   constexpr const_iterator cbegin() const noexcept { return begin(); }
   constexpr const_iterator cend() const noexcept { return end(); }
@@ -267,7 +268,7 @@ class span {
   }
 
  private:
-  T* data_;
+  UnownedPtr<T> data_;
   size_t size_;
 };