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Re: [Tooling] Modules naming

From: Tom Honermann <tom_at_[hidden]>
Date: Thu, 10 Jan 2019 22:26:58 -0500
On 1/10/19 5:17 PM, Ben Craig wrote:
> Can you elaborate more on the kinds of historical pains caused by
> tying a #include directive to a file name? I know of issues with
> #pragma once, but that feels like a distinct problem from file names.
> > This is based on decades of experience caused by header files.
> I think most of the participants in wg21 have years, often decades of
> experience with header files. I know of plenty of issues with the
> preprocessor, but I am not yet aware of any major problems on the file
> name front. (ok, getting the right slashes can be annoying… but it’s
> not a huge problem for me personally).
> I’m not a fan of the MANIFEST / module map approach in general. It
> requires duplicating information that is already in the source. I get
> that it has the potential to speed up builds, but I’d rather not have
> to update another location when I add a new .cpp file to my project.
> Many build systems allow for the user to make the tradeoff in whether
> they will use a file system glob to enumerate their source, or require
> the user to list the source manually. I usually fall into the file
> system glob crowd.
The manifest file could be generated (based on information in source
code) and usable by multiple tools, IDEs, and build systems. It need
not be a statically maintained file. I like this approach because it
appropriately separates the steps of identifying/building the module
name/file map vs using the module name/file map (most tools don't want
to be build systems).


> *From:* tooling-bounces_at_[hidden] <tooling-bounces_at_[hidden]>
> *On Behalf Of *Gabriel Dos Reis
> *Sent:* Thursday, January 10, 2019 3:15 PM
> *To:* WG21 Tooling Study Group SG15 <tooling_at_[hidden]>
> *Subject:* Re: [Tooling] Modules naming
> Microsoft strongly encourages its developers and customers to NOT tie
> a module name with the containing source file of its interface. This
> is based on decades of experience caused by header files. I would
> rather see us move in the direction of some sort of MANIFEST file that
> map modules to source files and artifacts.
> *From:* tooling-bounces_at_[hidden]
> <mailto:tooling-bounces_at_[hidden]> <tooling-bounces_at_[hidden]
> <mailto:tooling-bounces_at_[hidden]>> *On Behalf Of *Corentin
> *Sent:* Thursday, January 10, 2019 6:53 AM
> *To:* WG21 Tooling Study Group SG15 <tooling_at_[hidden]
> <mailto:tooling_at_[hidden]>>
> *Subject:* [Tooling] Modules naming
> Hello.
> I would like to suggest two modules related proposals that I think
> SG15 should look at.
> -*Compiler enforced mapping between module names and module interface
> file (resource) name. *
> Currently, modules interfaces can be declared in any file - which
> makes dependency scanning more tedious than it needs to be and have
> performance implications
> (The build system needs to open all files to gather a list of modules)
> - notably when the build system tries to start building while the
> dependency graph isn't yet complete.
> Tools ( ide, code servers, indexers, refactoring) may also greatly
> benefit from an easier way to locate the source file which declares a
> module.
> The specifics of the mapping are open to bikeshedding. However, I
> think we would have better luck sticking to something simple like
> <module identifier> <=> <file name>.<extension>
> (The standardese would mention /resource identifier/ rather than filename)
> - *A standing document giving guidelines for modules naming.*
> The goal is to take everything the community had to learn the hard way
> about header naming over the past 30 years and apply it to modules by
> providing a set of guidelines
> that could be partially enforced by build system vendors.
> Encouraging consistency and uniqueness of module identifiers across
> the industry is I think a necessary step towards sane package management.
> Note that the standard requires uniqueness of modules identifiers
> within (the standard definition of) a program but says little about a
> way to ensure this uniqueness.
> Here is a rough draft of what I think would be good guidelines,
> partially inspired by what is done by other languages facing similar
> issues.
> ·*Prefix module names with an entity and/or a project name to prevent
> modules from different companies, entities and projects of declaring
> the same module names.*
> ·*Exported top-level namespaces should have a name identic to the
> project name used as part of the name of the module(s) from which it
> is exported.*
> ·*Do not export multiple top-level namespaces*
> ·*Do not export entities in the global namespace outside of the global
> module fragment.*
> ·*Organize modules hierarchically.* For example, if both modules
> |example.foo| and |example.foo.bar| exist as part of the public API of
> |example|, |example.foo| should reexport |example.foo.bar|
> ·*Avoid common names such as *|util|* and *|core|* for module name
> prefix and top-level namespace names.*
> ·*Use lower-case module names*
> ·*Do not use characters outside of the basic source character set in
> module name identifiers.*
> My hope is that these 2 proposals (whose impact on the standard is
> minimal) would make it easier for current tooling to deal with modules
> while making possible for example to design dependency managers and
> build systems able to work at the module level.
> I'd love to gather feedback and opinions before going further in that
> direction.
> Thanks a lot!
> Corentin
> PS: For a bit of background, I talked about these issues there
> https://cor3ntin.github.io/posts/modules_mapping/
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__nam06.safelinks.protection.outlook.com_-3Furl-3Dhttps-253A-252F-252Fcor3ntin.github.io-252Fposts-252Fmodules-5Fmapping-252F-26data-3D02-257C01-257Cgdr-2540microsoft.com-257C1139eb25a2ca43b5cb2e08d6770b6606-257C72f988bf86f141af91ab2d7cd011db47-257C1-257C0-257C636827288180838903-26sdata-3DRbCelyBe1YDW4eNJtYEgKkAeHGxvkhsYqzPk0wf3F58-253D-26reserved-3D0&d=DwMGaQ&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=y8mub81SfUi-UCZRX0Vl1g&m=Yv6fjy4yWnfBkW_0m604prnwiQIO5K6DRLBHMjpiaxI&s=v7Z40T9WgivvxWUJ6plSphOw4d8bdvfEz9NAqCruKwE&e=>
> https://cor3ntin.github.io/posts/modules_naming/
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__nam06.safelinks.protection.outlook.com_-3Furl-3Dhttps-253A-252F-252Fcor3ntin.github.io-252Fposts-252Fmodules-5Fnaming-252F-26data-3D02-257C01-257Cgdr-2540microsoft.com-257C1139eb25a2ca43b5cb2e08d6770b6606-257C72f988bf86f141af91ab2d7cd011db47-257C1-257C0-257C636827288180838903-26sdata-3DtMhQa4ijeqUd2qxXV4loP47nU5NESRTKJLwZqe-252FI1fc-253D-26reserved-3D0&d=DwMGaQ&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=y8mub81SfUi-UCZRX0Vl1g&m=Yv6fjy4yWnfBkW_0m604prnwiQIO5K6DRLBHMjpiaxI&s=O9uUoT3QItO0vkb2QTG-EnXjsGfOiq7t93GgFz4YHx8&e=>
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Received on 2019-01-11 04:36:42