Tracking Issue for target-spec-json (flexible target specifications)

[ehuss]

This is a tracking issue for the RFC "Flexible target specification" (rust-lang/rfcs#131).

About tracking issues

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Overview

This is the tracking issue for the ability to specify custom targets using a file that defines the target (currently JSON).
See also #38338 for the related --print=target-spec-json.

Documentation: https://doc.rust-lang.org/nightly/rustc/targets/custom.html
Issues: A-target-specs Area: Compile-target specifications

Unresolved Questions

• Should the file format be JSON or something else like TOML?
  • See target-spec-toml draft davidtwco/rfcs#5 for a draft RFC proposal that also includes stability information.
• The format is somewhat tied to LLVM. There are some concerns that may make using other backends more difficult. Here is a suggestion for making the backend explicit.
• How will stability be handled?
• Validate that the standard library can be reliably built (no TARGET detection, see Target specification? wg-cargo-std-aware#6 (comment)).

Implementation history

• Original tracking issue: Implement flexible target specs #16093
• Initial implementation: Implement flexible target specification #16156
• Added --print target-spec-json: print option to dump target spec as JSON #38061
• Support for absolute paths: Introduce a TargetTriple enum to support absolute target paths #49019
• Added sysroot path search: Add default search path to Target::search() #83800
• Target search cleanup: Adjust target search algorithm for rustlib path #85152
• Added --print target-spec-json-schema: Add --print target-spec-json-schema #144498
• Destabilization:
  • Destabilise target-spec-json #150151
  • target: fix destabilising target-spec-json #151534
  • compiletest: -Zunstable-options for json targets #152236
  • Support JSON target specs in bootstrap #152677
  • [beta] Revert destabilise target-spec-json #152721
  • bootstrap: -Zjson-target-spec for synthetic targets #154428
  • Add -Z json-target-spec cargo#16557