Module future_incompat

Support for future-incompatible warning reporting.

Here is an overview of how Cargo handles future-incompatible reports.

Receive reports from the compiler

When receiving a compiler message during a build, if it is effectively a FutureIncompatReport, Cargo gathers and forwards it as a Message::FutureIncompatReport to the main thread.

To have the correct layout of strucutures for deserializing a report emitted by the compiler, most of structure definitions, for example FutureIncompatReport, are copied either partially or entirely from compiler/rustc_errors/src/json.rs in rust-lang/rust repository.

Persist reports on disk

When a build comes to an end, by calling save_and_display_report Cargo saves the report on disk, and displays it directly if requested via command line or configuration. The information of the on-disk file can be found in FUTURE_INCOMPAT_FILE.

During the persistent process, Cargo will attempt to query the source of each package emitting the report, for the sake of providing an upgrade information as a solution to fix the incompatibility.

Display reports to users

Users can run cargo report future-incompat to retrieve a report. This is done by OnDiskReports::load. Cargo simply prints reports to the standard output.

Structs

• Diagnostic
  A diagnostic emitted by the compiler as a JSON message. We only care about the ‘rendered’ field
• FutureBreakageItem
  A single future-incompatible warning emitted by rustc.
• FutureIncompatReport
  The future incompatibility report, emitted by the compiler as a JSON message.
• FutureIncompatReportPackage
  Structure used for collecting reports in-memory.
• OnDiskReport 🔒
  A single report for a given compilation session.
• OnDiskReports
  The structure saved to disk containing the reports.

Constants

• FUTURE_INCOMPAT_FILE 🔒
  The filename in the top-level target directory where we store the report
• MAX_REPORTS 🔒
  Max number of reports to save on disk.
• ON_DISK_VERSION 🔒
  Current version of the on-disk format.
• REPORT_PREAMBLE

Functions

• get_updates 🔒
  Returns a user-readable message explaining which of the packages in package_ids have updates available. This is best-effort - if an error occurs, None will be returned.
• render_report 🔒
• save_and_display_report
  Writes a future-incompat report to disk, using the per-package reports gathered during the build. If requested by the user, a message is also displayed in the build output.