Bug 1614512 - Give mozilla::Side and mozilla::Corner a fixed underlying type. r=froydnj

So as to avoid UB. It is somewhat unfortunate/dumb the fact that we need to do
this and we can't detect when we forget to do it :(

Give it uint8_t as it's type as that's enough and consistent with LogicalSide.

Differential Revision: https://phabricator.services.mozilla.com/D62390

--HG--
extra : moz-landing-system : lando

gfx/2d/Types.h

@@ -514,7 +514,7 @@ typedef mozilla::gfx::SurfaceFormat gfxImageFormat;
 namespace mozilla {
 
 // Side constants for use in various places.
-enum Side { eSideTop, eSideRight, eSideBottom, eSideLeft };
+enum Side : uint8_t { eSideTop, eSideRight, eSideBottom, eSideLeft };
 
 constexpr auto AllPhysicalSides() {
   return mozilla::MakeInclusiveEnumeratedRange(eSideTop, eSideLeft);
@@ -533,7 +533,7 @@ enum class SideBits {
 
 MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(SideBits)
 
-enum Corner {
+enum Corner : uint8_t {
   // This order is important!
   eCornerTopLeft = 0,
   eCornerTopRight = 1,

mfbt/EnumeratedRange.h

@@ -178,6 +178,13 @@ constexpr detail::EnumeratedRange<EnumType> MakeEnumeratedRange(EnumType aEnd) {
 }
 
 // Create a range to iterate from aBegin to aEnd, inclusive.
+//
+// NOTE: This internally constructs a value that is one past `aEnd`, so the
+// enumeration needs to either have a fixed underlying type, or `aEnd + 1` must
+// be inside the range of the enumeration, in order to not be undefined
+// behavior.
+//
+// See bug 1614512.
 template <typename EnumType>
 constexpr detail::EnumeratedRange<EnumType> MakeInclusiveEnumeratedRange(
     EnumType aBegin, EnumType aEnd) {