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Re: [Modules] Should the compiler try to build std module implicitly?

From: Tom Honermann <tom_at_[hidden]>
Date: Mon, 4 Dec 2023 12:31:17 -0500
If this can be done without too much difficulty, great.

However, would you expect this to work for both -stdlib=libc++ and
-stdlib=libstdc++? How about when Clang is used with Microsoft's
standard library (for which there is no corresponding -stdlib option)?


On 12/4/23 1:00 AM, Chuanqi Xu via SG15 wrote:
> Hi Guys,
> This post is mainly about some random thoughts about teachability
> of std modules. Also [P2412R0: Minimal module support for the standard
> library]
> (https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2412r0.pdf)
> mentions that the std module is important for educations and
> beginners. If there are more interests, I can try to summarize them
> into a paper.
> When I start to learn C++, I only need to copy a hello world
> example and run:
> ```
> clang++ hello.cpp -o hello
> ```
> However, with the current direction of std modules, the beginner
> need to install the build systems and try to copy the build scripts
> that them can hardly understand. Possibly some simpler form of
> https://libcxx.llvm.org/Modules.html. But it still seems scaring to
> beginners.
> And I am wondering if we can simplify the process. For example,
> the beginners can compile a hello world example with std module:
> ```
> import std;
> int main() { std::cout << "Hello modular world\n"; }
> ```
> with a single command line:
> ```
> clang++ -std=c++23 hello.cpp -o hello
> ```
> The compiler may achieve that when:
> - the std module is required but not provided.
> - the path to std module's BMI is not specified. (implied that the
> invocation doesn't from build systems)
> - the final output is an executable.
> - the std module's source exists in the installed path (being
> discussed in https://github.com/llvm/llvm-project/issues/73089).
> then the compiler can try to compile the std module's source to BMI
> and object file. Then we can import the BMI and link the object file.
> There are some details. e.g., where should we put the BMI? Should we
> try to reuse the BMIs? Can we extend the process to other modules?
> They are open questions and my answers are:
> - By default, they should be in `/tmp` and if `-save-temps` is
> specified, they'll be in the same directory with the temporaries.
> - The compiler shouldn't try to reuse the BMIs. That is the job of the
> build systems.
> - No, we can't. It is possible for std module since we'll try to
> standardize the locations of std modules sources. So that the tools
> are able to find the source of std modules. But it is not the case for
> other generalized modules. Also I think this is the job of build
> systems too.
> The motivation is primarily for beginners and educations. How do you
> feel about the idea?
> Thanks,
> Chuanqi
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Received on 2023-12-04 17:31:19