This flows out of #5084 and trying to reduce UnsafeMake use. It turns
out imports and namespaces were using unexpected node kinds (previously
ImportIntroducer instead of ImportDecl, for example). This fixes and
adds validation.
I was uncertain about whether to just remove the is_convertible check,
since I don't see it as motivating creation of a conversion between
NodeIdOneOf types. So I've just left a TODO for now.
This adds support for having different C++ `NameScope`s (and not just
the main `Cpp` scope), and we keep a pointer to `clang::DeclContext`
these scopes so we can look up C++ names in the right part of the AST.
C++ Interop Demo with a namespace:
```c++
// hello_world.h
namespace some_namespace {
void hello_world();
} // namespace some_namespace
```
```c++
// hello_world.cpp
#include <cstdio>
namespace some_namespace {
void hello_world() { printf("Hello World!\n"); }
} // namespace some_namespace
```
```carbon
// main.carbon
library "Main";
import Cpp library "hello_world.h";
fn Run() -> i32 {
Cpp.some_namespace.hello_world();
return 0;
}
```
```shell
$ clang -c hello_world.cpp
$ bazel-bin/toolchain/carbon compile main.carbon
$ bazel-bin/toolchain/carbon link hello_world.o main.o --output=demo
$ ./demo
Hello World!
```
Closes#5102
This removes some churn when adding new diagnostic cases to test files
(where previous to this change the newly added newline would cause the
previous diagnostic CHECKs to be updated including changes to the line
number because the CHECK for the blank line meant an extra line between
CHECK and source line).
A few alternatives discussed here:
https://discord.com/channels/655572317891461132/655578254970716160/1329573358475673723
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Boaz Brickner
Jon Ross-Perkins
Richard Smith
David BlaikieandJon Ross-Perkins