We're seeing some chrome bots fail unittests in ways that suspiciously
look like dynamic casts are doing Wrong Things.
The ClassID::Of() logic depends on the linker folding away duplicate
compilation unit definitions based on ODR rules. If we were to somehow
end up with different definitions, then we'd have two or more different
ClassIDs for the same T type - leading to issues similar to what we're
seeing.
I'm not entirely sure why/how this could happen - and we've so far been
entirely unable to locally reproduce - but it _might_ have something to
do with the goma cache.
In an attempt to work around this, move the static symbol definition out
of a header-local-static and into the .cc file for each of the types.
Change-Id: If914d3045b9dac6fbe8824dac71153a768cfceb9
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/34563
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
Implements `As<Blah>()` and `Is<Blah>()` automatically.
There are several benefits to using this over the pattern of hand-rolled `IsBlah()`, `AsBlah()` methods:
(1) We don't have to maintain a whole lot of hand written code.
(2) These allow us to cast from the base type to _any_ derived type in a single cast. The existing hand-rolled methods usually require a couple of intermediary casts to go from the base type to the leaf type.
(3) The use of a template parameter means these casts can be called from other template logic.
Note: Unlike the hand-rolled `AsBlah()` methods, it is safe to call `As<T>()` even if the type does not derive from `T`. If the object does not derive from `T` then `As` will simply return `nullptr`. This allows the calling logic to replace the common pattern of:
```
if (obj.IsBlah()) {
auto* b = obj.AsBlah();
...
}
```
with:
```
if (auto* b = obj.As<Blah>()) {
...
}
```
This halves the number of virtual method calls, and is one line shorter.
Change-Id: I4312e9831d7de6703a97184640864b8050a34177
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/34260
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
Ben Clayton