4d80df0922
We only define the classes in `<syncstream>` when experimental library features are enabled, but we would forward-declare them in `<iosfwd>` even when they are disabled. This led to confusing error messages about being unable to instantiate an undefined template.
The "module partitions" for the std module
The files in this directory contain the exported named declarations per header. These files are used for the following purposes:
- During testing exported named declarations are tested against the named declarations in the associated header. This excludes reserved names; they are not exported.
- Generate the module std.
These use cases require including the required headers for these "partitions" at different locations. This means the user of these "partitions" are responsible for including the proper header and validating whether the header can be loaded in the current libc++ configuration. For example "include " fails when locales are not available. The "partitions" use the libc++ feature macros to export the declarations available in the current configuration. This configuration is available if the user includes the `__config' header.
We use .inc files that we include from the top-level module instead of
using real C++ module partitions. This is a lot faster than module partitions,
see this for details.