Let's start this in SG15 to get tooling expert's thoughts, and figure out the language stuff with that knowledge.

Belfast 2019-11 Tooling Minutes

P1905R0 In-Source Mechanism to Identify Importable Headers

Chair: Bryce Adelstein Lelbach

Champion: Corentin Jabot

Minute Taker: Aaron Ballman

Start Review: 11-08 10:39

Start Polling: 11:07

POLL: We want an in-source mechanism for indicating but not enforcing that a header is importable.

Attendance: 16

Authors Voting: 1

Author Position: SF

A: Not clear what diagnostics are expected, concerns about how this impacts implementations that don't support implicit modules.

That has consensus.

POLL: We want an in-source mechanism for indicating but not enforcing that a header is NOT importable.

Attendance: 16

Authors Voting: 1

Author Position: SF

That has unanimous consent.

POLL: Prioritize scannability by tools in the design of a in-source mechanism that indicates whether headers are importable.

Attendance: 16

Authors Voting: 1

Author Position: SF

That has unanimous consent.

POLL: Explore an in-source mechanism for enforcing that a header must not be imported.

Attendance: 15

Authors Voting: 1

Author Position: F

That has unanimous consent.

POLL: Explore an in-source mechanism for enforcing that a header must only be imported.

Attendance: 15

Authors Voting: 1

Author Position: A

That has weak consensus.

End: 11:30

CONSENSUS: Bring a revision of P1905R0 (In-Source Mechanism to Identify Importable Headers), with the guidance below, to the Tooling Study Group.

• Retain the existing proposed in-source mechanism for indicating but not enforcing that a header is importable.
• Add an in-source mechanism for indicating but not enforcing that a header is NOT importable.
• Explore an in-source mechanism for enforcing that a header must not be imported.
• Explore an in-source mechanism for enforcing that a header must only be imported.
• Prioritize scannability by tools in the design of a in-source mechanism that indicates whether headers are importable.
• Make your design intent regarding scannability clear in the next revision; make it clear what's allowed to come before the #pragma.
• Prior to this paper returning, please get review from EWG, EWGI, or SG2, and also specifically Michael Spencer, GDR, and Nathan Sidwell.

This is ready for an EWGI and Modules Study Group pass. Note that if we don't want this in the International Standard, we still might want to suggest it in the Modules Ecosystem TR.

EWGI in Prague

The problem that P1905 is attempting to solve is worth solving.

The proper ship vehicle for this is the C++ Standard.

The proper ship vehicle for this is SG15 Ecosystem TR.

// The following polls taken in the context of a SG15 TR
We prefer the #pragma spelling listed as the choice in P1905.

We prefer an attribute spelling to solve the problem from P1905.

EWGI Believes that the Modules Ecosystem TR is the proper ship vehicle, and suggests a #pragma spelling.

Prague 2020-02 Tooling Minutes

P1905R0 In-Source Mechanism to Identify Importable Headers Modules

Chair: Ben Boeckel

Champion: Corentin Jabot

Minute Taker: Gor Nishanov

Start Review: 2020-02-14 17:10

Implementation experience: No.

POLL: We want to use #pragma importable to indicate an importable header.

Attendance: 15

# of Authors: 1

Author Position: SF

CONSENSUS: Weakly in favor.

POLL: We want to use #pragma not_importable to indicate a non-importable header.

Attendance: 15

# of Authors: 1

Author Position: SF

CONSENSUS: In favor.

POLL: We want to reject _Pragma(importable) and _Pragma(not_importable) conversion into #pragma.

Attendance: 15

# of Authors: 1

Author Position: SF

CONSENSUS: Weakly in favor.

Bruno volunteers to coauthor.

End: 15:32

CONSENSUS: Bring a revision of P1905R0 (In-Source Mechanism to Identify Importable Headers Modules), with the guidance below, to the Tooling Study Group for further review for the Modules Ecosystem Technical Report.

• Include #pragma importable and #pragma not_importable.
• Explore whether we can reject _Pragma(importable) and _Pragma(not_importable).