[PATCH] D131388: [docs] Add "C++20 Modules"

[Daniel Ruoso via Phabricator via cfe-commits]

ruoso added inline comments.


================
Comment at: clang/docs/CPlusPlus20Modules.rst:70-76
+* Primary module interface unit.
+
+* Module implementation unit.
+
+* Module partition interface unit.
+
+* Module partition implementation unit.
----------------
ChuanqiXu wrote:
> ruoso wrote:
> > The terminology here is a bit different than what we've been building the consensus on. Please take a look at [[ https://github.com/cplusplus/modules-ecosystem-tr/blob/master/sourcefiles.tex#L19 | sourcefiles.tex ]] (or section `[source.types]` in the [[ 
> > https://github.com/cplusplus/modules-ecosystem-tr/files/9237071/iso_cpp_modules_ecosystem_technical_report.pdf | rendered version ]] 
> > 
> > 
> If there is a consensus already, we should follow. 
> 
> (BTW, I thought we'll discuss module things in SG2 but it looks like we're discussing them in SG15... my bad)
Yes, please consider joining us for the sg15 meetings, we've been working through quite a few things related to C++ modules.


================
Comment at: clang/docs/CPlusPlus20Modules.rst:225
+
+It is possible to generate a module file for an importable module unit by specifying the ``--precompile`` option.
+
----------------
ChuanqiXu wrote:
> ruoso wrote:
> > Likewise, here the term "Built Module Interface file", with the acronym "BMI" is what we're generally using when talking about the generated file.
> Yeah, this is what I was confused in the chat. In my mind, "BMI" describes a compatible interface format like ABI (like Itanium ABI). In another words, a BMI could be compiled by compiler which follows the BMI standard (like clang and gcc both accepts Itanium ABI). But currrently, a module file couldn't be compiled by clang in different versions.
> 
> So from my point of view, the term `module file` is more appropriate than `BMI` now.
BMI is definitely not as compatible as the ABI. I think there's some confusion here of what the term BMI is. In this case the `pcm` file is the BMI.


================
Comment at: clang/docs/CPlusPlus20Modules.rst:243-244
+
+The option ``-fprebuilt-module-interface`` tells the compiler the path where to search for dependent module files.
+It may be used multiple times just like ``-I`` for specifying paths for header files.
+
----------------
ChuanqiXu wrote:
> ruoso wrote:
> > Is that the case for C++20 named modules as well? I thought this was just for clang modules. How does the lookup work?
> In this document, modules are referring to `C++20 Named Modules` by default. The option is borrowed from clang modules. The look up rule here is:
> 
> (1) When we import module `M`. The compiler would look up `M.pcm` in the directories specified by ``-fprebuilt-module-interface``.
> (2) When we import partition module unit `M:P`. The compiler would look up `M-P.pcm` in the directories specified by ``-fprebuilt-module-interface``.
> 
> I thought this is clear enough. Do you have suggestion to improve? I am a little worried to be wordy.
Yes, thanks for the clarification. I think it would be worth including a description of how the lookup works as a part of the doc.


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https://reviews.llvm.org/D131388