Adding cpu usage in cargo log

[Suryansh-Dey]

Add CPU usage data to cargo report timings

Summary

This PR adds CPU usage tracking to the log files generated by -Z build-analysis, enabling cargo report timings to reconstruct and display CPU usage graphs in the HTML timing report.

Previously, CPU usage data was only available in the live --timings path (collected in-memory by record_cpu() and passed directly to RenderContext). When using cargo report timings to reconstruct a report from log files, the CPU usage graph was always empty — even though the HTML legend still displayed a "CPU Usage" entry.

Closes #16651

Changes

src/cargo/util/log_message.rs

• Added CpuUsage { elapsed: f64, usage: f64 } variant to the LogMessage enum, representing a periodic CPU usage sample.

src/cargo/core/compiler/timings/mod.rs

• In finished(), log all accumulated CPU usage samples to the file logger before generating the HTML report.
• Moved CPU logging outside the get_logs() guard (which only succeeds for --timings) into the outer if let Some(logger) block, so data is written whenever any logger exists (including the file logger used by -Z build-analysis).
• Updated the live path to use Cow::Borrowed for the cpu_usage field.

src/cargo/core/compiler/timings/report.rs

• Changed RenderContext::cpu_usage from &'a [(f64, f64)] to Cow<'a, [(f64, f64)]> to support both borrowed data (live --timings path) and owned data (log reconstruction path).

src/cargo/ops/cargo_report/timings.rs

• Added handling of LogMessage::CpuUsage in prepare_context() to collect CPU samples from log files and store them as Cow::Owned in the render context.

Updating tests

Added a "{...}" trailing wildcard to match the cpu-usage entries, same pattern used by other tests in the file (e.g., log_rebuild_reason_fresh_build). Also proactively applied the same fix to log_msg_timing_info_section_timings (nightly-only test) for consistency.

Testing

• All existing cargo_report_timings tests pass (16 passed, 1 ignored for nightly-only).
• All existing timings tests pass.
• End-to-end verified: built a project with CARGO_BUILD_ANALYSIS_ENABLED=true cargo check -Z build-analysis, confirmed 120 cpu-usage entries in the log file, and verified cargo report timings produces an HTML report with populated CPU_USAGE JavaScript data.

Sample log entry:

{"reason":"cpu-usage","elapsed":1.255,"usage":76.72}

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• Owners of files modified in this PR: @ehuss, @epage, @weihanglo
• @ehuss, @epage, @weihanglo expanded to ehuss, epage, weihanglo
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[epage]

Note that #16651 was marked S-needs-design which means it isn't ready yet for implementation and review, see https://doc.crates.io/contrib/issues.html#issue-status-labels

[Suryansh-Dey]

Note that #16651 was marked S-needs-design which means it isn't ready yet for implementation and review, see https://doc.crates.io/contrib/issues.html#issue-status-labels

I may update or tweak my PR later according to yous discussions. Just a plan proposal because I found it interesting to work upon.

[epage]

s. Just a plan proposal because I found it interesting to work upon.

If your intent is just that, then I would either recommend keeping it local or communicating your intent and marking it as a Draft.