PrintAsClang is supposed to emit declarations in the same order regardless of the compiler’s internal state, but we have repeatedly found that our current criteria are inadequate, resulting in non-functionality-affecting changes to generated header content. Add a diagnostic that’s emitted when this happens soliciting a bug report.
Since there *should* be no cases where the compiler fails to order declarations, this diagnostic is never actually emitted. Instead, we test this change by enabling `-verify` on nearly all PrintAsClang tests to make sure they are unaffected.
This did demonstrate a missing criterion that only mattered in C++ mode: extensions that varied only in their generic signature were not sorted stably. Add a sort criterion for this.
The generated header would not compile without these dependencies. Moreover
users probably expect all-public option to be the most permissive filter
including the maximal amount of declarations.
The frontend option '-clang-header-expose-module' allows the user to specify that APIs from an imported module have been exposed in another generated header, and thus APIs that depend on them can be safely exposed in the current generated header.
