US133 15.03 Header units containing internal-linkage entities P2003 P1815

[wg21bot]

It is not clear whether header-unit source code can contain internal-linkage entities.  For example the iostream header can contain:
  static ios_base::Ioinit __ioinit;
Is that permitted, or does it make the header file incompatible with being a header unit?

Proposed change:
Preference for internal linkage entities to be an error.  Thus library implementors will need an (implementation-defined) mechanism to know whether the header file is being textually included, or whether it is being processed to create a header-unit.

[jfbastien]

From the Belfast discussion:

Poll: EWG encourages further work to solve the issue of internal-linkage-entities in header units for C++20
SF F N A SA 17 9 0 0 0
Motion passes

Poll: Accept the proposed change in US133 for C++20
SF F N A SA 0 4 1 12 7
Motion does not pass

[jfbastien]

See P2003 Fixing Internal and External Linkage Entities in Header Units cplusplus/papers#740

[jensmaurer]

Wording integrating in P1815.

[jensmaurer]

CWG in Prague: Accepted with modification. See paper P1815R2.