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Greptile SummaryThis change adds Rust pprof tracing documentation alongside Rust trace conversion support. Two documented Rust recording behaviors were reproduced: the profile-writing snippet does not compile without importing the protobuf Confidence Score: 4/5The Rust tracing implementation should not be considered ready to merge until the recording documentation is corrected, because the advertised copy-and-run workflow fails to compile. The two documented behaviors were reproduced with minimal Rust/Cargo harnesses: one demonstrated the exact compiler failure and its required import, and the other compared optimized release builds while changing only debug-information generation. Files Needing Attention:
 T-Rex LogsWhat T-Rex did
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![greptile-apps[bot]](https://avatars.githubusercontent.com/in/867647?s=60&v=4){kind=small}
| run_the_workload(); | ||
| if let Ok(report) = guard.report().build() { | ||
| let mut file = std::fs::File::create("cpu.pb.gz").unwrap(); | ||
| report.pprof().unwrap().write_to_writer(&mut file).unwrap(); |
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The recording snippet calls write_to_writer without bringing the protobuf Message trait into scope. Copying the documented pprof = { version = "0.13", features = ["protobuf-codec"] } recipe fails with E0599 before it can write a profile. Add use pprof::protos::Message; to the snippet.
Artifacts
Copied Rust recipe without the Message trait import
- Minimal source copied from the documented recipe and compiled unchanged, showing the missing import condition; takeaway: this is the failing input.
Corrected Rust recipe with the Message trait import
- The same minimal source with only `use pprof::protos::Message;` added, used for the successful comparison; takeaway: this is the required correction.
Cargo manifest pinning pprof 0.13 with protobuf-codec
- Cargo manifest used by both runs pins the documented pprof dependency and feature; takeaway: the reproduction matches the stated dependency scope.
Executable before and after Cargo harness
- Shell harness that compiles the copied recipe first and then the trait-imported variant, capturing both command outputs; takeaway: the comparison is repeatable.
Cargo compile failure for the copied documentation recipe
- Captured `cargo run --release` output exits 101 with E0599 and recommends importing `pprof::protos::Message`; takeaway: the documented snippet does not compile.
Cargo compile success after importing Message
- Captured `cargo run --release` output exits 0 after adding the required trait import; takeaway: the one-line import fixes compilation.
Corrected pprof harness runtime output
- Captured release execution exits 0 and confirms nonempty output beginning with protobuf bytes `0a 04 08`; takeaway: the corrected recipe runs and writes profiling data.
Prompt To Fix With AI
This is a comment left during a code review.
Path: docs/guide/dynamic-tracing.md
Line: 273
Comment:
**Rust profile writer lacks its trait import**
The recording snippet calls `write_to_writer` without bringing the protobuf `Message` trait into scope. Copying the documented `pprof = { version = "0.13", features = ["protobuf-codec"] }` recipe fails with E0599 before it can write a profile. Add `use pprof::protos::Message;` to the snippet.
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For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.|
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| Sampled stacks make `dyn Trait` dispatch and calls through function pointers | ||
| visible; counts are sample counts, so give the workload enough CPU time, and | ||
| build with reduced inlining (`opt-level = 0` or `debug = true`) or inlined |
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debug = true retains symbols and line tables, but it does not reduce or disable inlining in an optimized release build. Presenting it as an alternative to opt-level = 0 can leave profiled callees inlined and absent from the sampled call graph. Keep debug = true as symbol and line-table guidance, and recommend an optimization-level change when reduced inlining is required.
Artifacts
Minimal Rust release workload source
- Defines an ordinary candidate call and an inline-never control used to compare release compilation with debug information disabled and enabled, with the takeaway that symbol presence and call output directly expose the inlining outcome.
Reproducible Cargo release profile runner
- Builds the same opt-level 3 Cargo release workload with only debug=false or debug=true changed, runs it, and inspects symbols and workload disassembly, with the takeaway that the validation can be repeated exactly.
Release build output with debug information disabled
- Captured command output for the debug=false release build shows the runtime result, no candidate symbol, and the inline-never control symbol, with the takeaway that the baseline optimized build inlines the candidate.
Release build output with debug information enabled
- Captured command output for the debug=true release build shows the same runtime result, no candidate symbol, and the inline-never control symbol, with the takeaway that enabling debug information did not reduce inlining.
Prompt To Fix With AI
This is a comment left during a code review.
Path: docs/guide/dynamic-tracing.md
Line: 286
Comment:
**Debug information does not reduce release inlining**
`debug = true` retains symbols and line tables, but it does not reduce or disable inlining in an optimized release build. Presenting it as an alternative to `opt-level = 0` can leave profiled callees inlined and absent from the sampled call graph. Keep `debug = true` as symbol and line-table guidance, and recommend an optimization-level change when reduced inlining is required.
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For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!
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@greptile-apps Both fixed in eeac19d (docs-only):
Also switched the snippet to write |
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Both fixes are confirmed in
LGTM on the docs fix. No further concerns. |
What
Adds a dynamic call-graph tracer for Rust, the last runtime in the epic (#1244) with no tracer.
pprof-rs/cargo flamegraphwrite gzipped protobuf CPU profiles in the same wire format as Go, so this reuses the Go pprof decoder and accumulation and adds only Rust-specific symbol demangling and scoping.Why
Static analysis already resolves monomorphised Rust calls, so the dynamic payoff is narrower but real:
dyn Traitdispatch, function pointers, and closures routed across boundaries. This closes #1251.Approach
codebase_rag/trace/rust_pprof.py:convert_rust_pprofreuses_decompress/_decode_profile/_accumulate_edgesfrompprof.py; a Rust_bare_namestrips the legacy::h<hash>, splits paths at angle/paren depth zero so<Dog as Animal>::speakyieldsspeak, drops trailing turbofish (fn::<u32>->fn), collapses generic instantiations, and marks{{closure}}anonymous. Frames outside the repo and undertarget/are seen through to the nearest project frame. The header is taggedsampled=True(pprof-rs samples).JsFrameResolver(span-first, bare name + declaration line), so monomorphised instances resolve to their single generic source definition;ingest.pyaddsrustto that dispatch tuple.cgr trace convert --language rustselects the Rust demangler. Unknown--languagevalues are rejected.Tests
dyn Traitdispatch edge captured through an intervening std frame,target/+stdlib frames out of scope, closures/generics normalised,_bare_namedemangling table, workload labelling, malformed-profile rejection.dynamic_sampled+static_missed.--language rustroutes to the Rust converter (and needs--repo-path); unknown language rejected. Plus theTRACE_LANGUAGE_RUSTconstant assertion.Stacked on #1273 (the
sampledinterchange flag it depends on). Closes #1251. Refs #1244.