rust: Portfile can fail to parse depending on build_arch

[jmroot (Joshua Root)]

For example, on macOS 12:

% port info rust build_arch=i386
Error: Unable to open port: can't read "rustc_version": no such variable

It's fine for the port to only be installable for certain archs, but the Portfile should parse validly regardless of what platform or arch it is read on. This is probably what is preventing rust from showing up on ports.macports.org.

[herbygillot (Herby Gillot)]

Reassigning to MarcusCalhoun-Lopez who has made massive changes to the Rust port, which look like the origin of this issue.

[MarcusCalhoun-Lopez (Marcus Calhoun-Lopez)]

Clearly, a port should always be able to parse validly regardless of platform or architecture.
Anything less should be fixed right away.

However, I cannot reproduce this error.
The command port info rust build_arch=i386 does not produce an error on my system:

macOS 10.12.6 16G2136 x86_64
Xcode 9.2 9C40b
Command Line Tools 9.2.0.0.1.1510905681

So we must now figure out what is different about the system where the error does occur.

This is just a guess, but port info rust muniversal.architectures="" did produce an error on my system.

muniversal.architectures should not be empty, but if it were, the error could be traced as follows:

• from ​the end proc rust.add_bootstrap_components
• since rustc_version is not set in ​in the for loop
• since muniversal.architectures ​is empty

Is there any reason to suspect that muniversal.architectures ​is empty on the system where the error occurs?

[jmroot (Joshua Root)]

Yes, muniversal.architectures would be empty in any case where build_arch is empty (normal on platforms other than macOS) or set to an arch that is not supported by the current SDK.

[MarcusCalhoun-Lopez (Marcus Calhoun-Lopez)]

There is a ​pull request that might solve the problem.
Unfortunately, I do not know how to properly test it.

[jmroot (Joshua Root)]

An easy way to test is to run port info rust build_arch=. The fix looks good, thanks.

[MarcusCalhoun-Lopez (Marcus Calhoun-Lopez)]

In dc95280770aaefc0ddda81981def0f1e4c7a5f46/macports-ports (master):

rust PG: ensure parse success on non-macOS systems

Fixes #65183