[cfe-dev] Will Clang use PCH format to implement C++20 module system?

[David Blaikie via cfe-dev]

It won't - there are no plans for precompiled modules to be portable
between compilers. (someone at Microsoft has been having some discussions
about maybe making some of that possible - but there's a fair bit of
resistance, and so far as I know from Clang and GCC there's no work in that
direction)

On Tue, Jan 7, 2020 at 4:10 AM Yafei Liu <yfliu at mobvoi.com> wrote:

> Hey David, I got another question, do you know how will Clang handle
> modules which is compiled by other compiler? For example GCC? The AST
> serialization is not the same.
>
> On Tue, Jan 7, 2020 at 2:30 AM David Blaikie <dblaikie at gmail.com> wrote:
>
>>
>>
>> On Mon, Jan 6, 2020 at 2:28 AM Yafei Liu via cfe-dev <
>> cfe-dev at lists.llvm.org> wrote:
>>
>>> Hi all, I'm curious if the PCH format will be used to implement C++20
>>> module system? Any Clang community discussions or documents on this?
>>>
>>
>> More or less. The basic AST serialization system is already shared
>> between PCH, Clang Header Modules, and preliminary support for C++20
>> Modules. Not exactly the same, because the semantics of each are slightly
>> different - but the core AST serialization is common across all 3.
>>
>>
>>> What's more, I'm inventing a language using LLVM, and I want to generate
>>> some middle layer to communicate with c++ module, so is there any tools or
>>> apis to generate a PCH?
>>>
>>
>> None that I know of. The only cross-language binding like that that I
>> know of is Swift, which is one-way to the best of my knowledge (so Swift
>> doesn't have to generate Clang-compatible AST files (PCH/PCM/whatever) - it
>> only has to be able to read them). I imagine Swift's binary module
>> representation might be similar for ease of interoperability, but I don't
>> actually know.
>>
>> - Dave
>>
>
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