[RFC,01/21] Documentation: add comparison of build systems

Commit Message

Patrick Steinhardt Oct. 2, 2024, 3:15 p.m. UTC

We're contemplating whether to eventually replace our build systems with
a build system that is easier to use. Add a comparison of build systems
to our technical documentation as a baseline for discussion.

Signed-off-by: Patrick Steinhardt <[e-mail]>
---
 Documentation/Makefile                    |   1 +
 Documentation/technical/build-systems.txt | 164 ++++++++++++++++++++++
 2 files changed, 165 insertions(+)
 create mode 100644 Documentation/technical/build-systems.txt

Comments

Junio C Hamano Oct. 2, 2024, 6:14 p.m. UTC | #1

Patrick Steinhardt <[e-mail]> writes:

> We're contemplating whether to eventually replace our build systems with
> a build system that is easier to use. Add a comparison of build systems
> to our technical documentation as a baseline for discussion.
>
> Signed-off-by: Patrick Steinhardt <[e-mail]>
> ---

Thanks for starting this.

> diff --git a/Documentation/technical/build-systems.txt b/Documentation/technical/build-systems.txt
> new file mode 100644
> index 0000000000..8fac36ce1d
> --- /dev/null
> +++ b/Documentation/technical/build-systems.txt
> @@ -0,0 +1,164 @@
> += Build Systems
> +
> +The build system is the primary way for both developers and system integrators
> +to interact with the Git project. As such, we consider it important to pick a
> +build system that fulfills our requirements while being easy to use and extend.

Maybe it is me, but this sounds as if _we_ do not need "easy to use
and extend", but "easy to use and extend" are extra afterthought
consideration we are making for others, which is a bit disturbing.

Let me try paraphrasing what I think you wanted to say

	As such, being easy to use and extend for those who are not
	directly developing Git itself is just as important as other
	requirements we have on any potential build system.

which hopefully would sound more like we are not treating those who
only build and tweak the product of our project as second-class
citizens.

> +This document outlines the different requirements that we have for the build
> +system and then compares available build systems using these criteria.
> +
> +== Requirements
> +
> +The following subsections prevent a list of requirements that we have for any

I think you meant "present".

> +potential build system. Sections are sorted by decreasing priority, even though
> +these priorities will naturally differ between users.
> +
> +=== Platform support
> +
> +The most important criterium is whether the build system supports all of the
> +platforms that Git supports. The most important platforms include:

Maybe it is just me, but when I hear "The most", I expect an
exhaustive list (hence "include" that came later somewhat surprised
me), and I consider these "the more important systems" (implying
"than others").

> +  - Linux
> +  - macOS
> +  - Windows
> +  - FreeBSD
> +  - OpenBSD
> +  - NetBSD
> +
> +The platforms which must be supported by the tool should be aligned with our
> +[platform support policy](platform-support.txt).

> +Auto-detection of the following items is considered to be important:
> +
> +  - Check for the existence of headers.
> +  - Check for the existence of libraries.
> +  - Check for the existence of exectuables.
> +  - Check for the runtime behavior of specific functions.

- Check for specific link order requirements when multiple libraries
  are involved.

> +=== Ease of use
> +
> +The build system SHOULD be both easy to use and easy to extend. While this is
> +naturally a subjective metric it is likely not controversial to say that some
> +build systems are considerably harder to use than others.

If we want to pull RFC-2119/BCP-14 with shouting "SHOULD", we
probably should use something similar in the previous "Platform
support" section.

> +=== IDE support
> +=== Out-of-tree builds

Cross platform builds (e.g., building for arm on x86-64 host)?

> +=== Rust support
> +
> +Many long-time Git contributors are nowadays in favor of adopting Rust as a
> +second language next to C. The build system SHOULD thus support Rust such that
> +we do not have to reopen the discussion once we decide to pick up Rust.

What reasons do you have in mind that, without spelling this out,
Rust will be left behind while C is fully supported?  If the build
system can keep track of dependencies by knowing foo.o is made from
foo.c and turning foo.c into foo.o takes running cc, it can do the
same for rustc.  Do you mean include file dependencies and the like?

If the reason why we say "Language X needs to be supported" is
because it is not enough to be able to run a compiler on source
files written in the language, but it is also necessary to know when
to run the compiler (i.e., by dependency tracking), it is better to
spell it out.

In any case, instead of singling out Rust in the title, name the
section "languate support", and give an enumeration of compilers
languages, processors that we care about, just like we did for
platforms.  For exaple, we may not necessarily want to treat "C
support, done as an afterthought of supporting C++" and "C support,
done natively" as equivalents (of course, the latter is better).

Shouldn't it also "support" asciidoc/asciidoctor/makeinfo for
the documentation toolchain?

Are there other things we use Makefile for in our current system
that we are forgetting in this requirements section, like "running
lint" or "running tests"?

Thanks.

Eric Sunshine Oct. 2, 2024, 8:24 p.m. UTC | #2

On Wed, Oct 2, 2024 at 11:16 AM Patrick Steinhardt <[e-mail]> wrote:
> We're contemplating whether to eventually replace our build systems with
> a build system that is easier to use. Add a comparison of build systems
> to our technical documentation as a baseline for discussion.
>
> Signed-off-by: Patrick Steinhardt <[e-mail]>
> ---
> +=== Rust support
> +
> +Many long-time Git contributors are nowadays in favor of adopting Rust as a
> +second language next to C. The build system SHOULD thus support Rust such that
> +we do not have to reopen the discussion once we decide to pick up Rust.

I've been watching the Rust discussion mostly from the sidelines, so
it's possible that I've missed something, but I was more than a little
surprised to see the claim that "Many long-time Git contributors [are]
in favor of adopting Rust" since my impression of the discussions does
not reflect that claim, nor could I find sufficient references to
support such a strong statement. My understanding of the situation is
rather different; I've seen both proponents and opponents. With
regards to project regulars...

* The most vocal proponent has been brian who gives the impression of
being quite a fan of Rust, but hasn't provided particularly compelling
reasons to adopt it, and some of his arguments are highly subjective
(for instance, "Rust excels at multithreading"[1]; while it's true
that Rust may make multithreading safer, it is highly subjective to
say that it "excels" at it -- especially, for instance, for anyone
familiar with Go's approach to the same subject).

* The Google team is interested in having a Rust wrapper for core Git
library[2], but that doesn't imply or require adopting Rust into the
Git project itself.

* Randall has severe misgivings[3] about Rust being introduced into
the project due to its exclusionary nature with regards to the
platform(s) he supports.

* At least one well-established contributor has stated[4] that "Rust
scares" him. (Possibly this was said somewhat in jest, but I suspect
the feeling may be shared by more than a few long-time Git
contributors who see Rust as an overly complex, complicated, and
convoluted language but who haven't spoken up because they understand
that the programming world in general is moving toward more modern
languages such as Rust and Go.)

* The only properly compelling arguments I've seen in favor of
adopting Rust came from Elijah[5,6] who is always well-spoken,
well-reasoned, thorough, and backs up his statements with plenty of
factual evidence.

Those aside, I don't recall seeing any other long-time Git
contributors speak up in favor of adopting Rust.

[1]: https://lore.kernel.org/git/[e-mail]/
[2]: https://lore.kernel.org/git/[e-mail]/
[3]: https://lore.kernel.org/git/053f01db0b79$0d885b30$28991190$@nexbridge.com/
[4]: https://lore.kernel.org/git/[e-mail]/
[5]: https://lore.kernel.org/git/CABPp-BFWsWCGogqQ=[e-mail]/
[6]: https://lore.kernel.org/git/CABPp-BFOmwV-xBtjvtenb6RFz9wx2VWVpTeho0k=[e-mail]/

Patch

diff --git a/Documentation/Makefile b/Documentation/Makefile
index 0f55baa252..e23cffb5f9 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -111,6 +111,7 @@  TECH_DOCS += MyFirstObjectWalk
 TECH_DOCS += SubmittingPatches
 TECH_DOCS += ToolsForGit
 TECH_DOCS += technical/bitmap-format
+TECH_DOCS += technical/build-systems
 TECH_DOCS += technical/bundle-uri
 TECH_DOCS += technical/hash-function-transition
 TECH_DOCS += technical/long-running-process-protocol
diff --git a/Documentation/technical/build-systems.txt b/Documentation/technical/build-systems.txt
new file mode 100644
index 0000000000..8fac36ce1d
--- /dev/null
+++ b/Documentation/technical/build-systems.txt
@@ -0,0 +1,164 @@ 
+= Build Systems
+
+The build system is the primary way for both developers and system integrators
+to interact with the Git project. As such, we consider it important to pick a
+build system that fulfills our requirements while being easy to use and extend.
+
+This document outlines the different requirements that we have for the build
+system and then compares available build systems using these criteria.
+
+== Requirements
+
+The following subsections prevent a list of requirements that we have for any
+potential build system. Sections are sorted by decreasing priority, even though
+these priorities will naturally differ between users.
+
+=== Platform support
+
+The most important criterium is whether the build system supports all of the
+platforms that Git supports. The most important platforms include:
+
+  - Linux
+  - macOS
+  - Windows
+  - FreeBSD
+  - OpenBSD
+  - NetBSD
+
+The platforms which must be supported by the tool should be aligned with our
+[platform support policy](platform-support.txt).
+
+=== Auto-detection of supported features
+
+The build system MUST support auto-detection of features which are or aren't
+available on the current platform. Platform maintainers should not be required
+to manually configure the complete build.
+
+Auto-detection of the following items is considered to be important:
+
+  - Check for the existence of headers.
+  - Check for the existence of libraries.
+  - Check for the existence of exectuables.
+  - Check for the runtime behavior of specific functions.
+
+=== Ease of use
+
+The build system SHOULD be both easy to use and easy to extend. While this is
+naturally a subjective metric it is likely not controversial to say that some
+build systems are considerably harder to use than others.
+
+=== IDE support
+
+The build system SHOULD integrate with well-known IDEs. Well-known IDEs include:
+
+  - Microsoft Visual Studio
+  - Visual Studio Code
+  - Xcode
+
+There are four levels of support:
+
+  - Native integration into the IDE.
+  - Integration into the IDE via a plugin.
+  - Integration into the IDE via generating a project description with the build
+    system.
+  - No integration.
+
+Native integration is preferable, but integration via either a plugin or by
+generating a project description via the build system are considered feasible
+alternatives.
+
+Another important distinction is the level of integration. There are two
+features that one generally wants to have:
+
+  - Integration of build targets.
+  - Automatic setup of features like code completion with detected build
+    dependencies.
+
+The first bullet point is the bare minimum, but is not sufficient to be
+considered proper integration.
+
+=== Out-of-tree builds
+
+The build system SHOULD support out-of-tree builds. Out-of-tree builds allow a
+developer to configure multiple different build directories with different
+configuration, e.g. one "debug" build and one "release" build.
+
+=== Rust support
+
+Many long-time Git contributors are nowadays in favor of adopting Rust as a
+second language next to C. The build system SHOULD thus support Rust such that
+we do not have to reopen the discussion once we decide to pick up Rust.
+
+== Comparison
+
+The following list of build systems are considered:
+
+- GNU Make
+- autoconf
+- CMake
+- Meson
+
+=== GNU Make
+
+- Platform support: ubitquitous on all platforms, but not well-integrated into Windows.
+- Auto-detection: no built-in support for auto-detection of features.
+- Ease of use: easy to use, but discovering available options is hard. Makefile
+  rules can quickly get out of hand once reaching a certain scope.
+- IDE support: execution of Makefile targets is supported by many IDEs
+- Out-of-tree builds: supported in theory, not wired up in practice.
+- Rust: can be added.
+
+=== autoconf
+
+- Platform support: ubiquitous on all platforms, but not well-integrated into Windows.
+- Auto-detection: supported.
+- Ease of use: easy to use, discovering available options is comparatively
+  easy. The autoconf syntax is prohibitively hard to extend though due to its
+  complex set of interacting files and the hard-to-understand M4 language.
+- IDE support: no integration into IDEs at generation time. The generated
+  Makefiles have the same level of support as GNU Make.
+- Out-of-tree builds: supported in theory, not wired up in practice.
+- Rust: not supported.
+
+=== CMake
+
+- Platform support: not as extensive as GNU Make or autoconf, but all major
+  platforms are supported.
+  - AIX
+  - Cygwin
+  - FreeBSD
+  - Linux
+  - OpenBSD
+  - Solaris
+  - Windows
+  - macOS
+- Ease of use: easy to use, discovering available options is not always
+  trivial. The scripting language used by CMake is somewhat cumbersome to use,
+  but extending CMake build instructions is doable.
+- IDE support: natively integrated into Microsoft Visual Studio. Can generate
+  project descriptions for Xcode. An extension is available for Visual Studio
+  Code. Many other IDEs have plugins for CMake.
+- Out-of-tree builds: supported.
+- Rust: not supported.
+
+=== Meson
+
+- Platform: not as extensive as GNU Make or autoconf, but all major platforms
+  and some smaller ones are supported.
+  - AIX
+  - Cygwin
+  - DragonflyBSD
+  - FreeBSD
+  - Haiku
+  - Linux
+  - NetBSD
+  - OpenBSD
+  - Solaris
+  - Windows
+  - macOS
+- Ease of use: easy to use, discovering available options is easy. The
+  scripting language is straight-forward to use.
+- IDE support: Supports generating build instructions for Xcode and Microsoft
+  Visual Studio, a plugin exists for Visual Studio Code.
+- Out-of-tree builds: supported.
+- Rust: supported.