Fixed wrong MRuby::Build.current at the top level of mrbgem.rake

[dearblue]

Until now, GEMS added via gem.add_dependency retained the last MRuby::Build.current from the build configuration file, which was accessible from the top level of mrbgem.rake.

[gemini-code-assist]

Summary of Changes

Hello @dearblue, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves an issue where the global MRuby::Build.current context could become incorrect when loading mrbgem.rake files, particularly for gems added as dependencies. The changes implement a mechanism to temporarily switch to the correct build context before loading an mrbgem.rake file and then reliably restore the previous context, ensuring that gem configurations are processed with the intended build settings.

Highlights

• Correct MRuby::Build.current Context: Ensures that the MRuby::Build.current variable is correctly set to the specific build configuration when an mrbgem.rake file is loaded, preventing it from retaining an incorrect context from previous build configurations.
• Robust Context Restoration: Introduces a begin...ensure block around the load gemrake call, guaranteeing that the original MRuby::Build.current context is always restored after the mrbgem.rake file has been processed, even if an error occurs during its loading.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a bug where MRuby::Build.current was not restored after loading a gem's mrbgem.rake file, which could cause issues with subsequent gem loading. The use of a begin..ensure block to manage this global state is a robust solution. The code is well-structured, and I have one suggestion to further improve its clarity by removing a redundant check.

[gemini-code-assist]

The check self.is_a?(MRuby::Build) appears to be redundant. The gem method is part of the MRuby::LoadGems module, which is included in MRuby::Build. All call sites seem to confirm that self is always an instance of MRuby::Build. You can simplify this line for better readability.

      build = self