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Setup tracing-tree for hierarchical debug traces - #7188
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Example for full lib crate, after inserting some 
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r? @ytmimi |
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jieyouxu
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Oct 16, 2026
jieyouxu
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Oct 16, 2026
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| let layer = HierarchicalLayer::default() | ||
| .with_writer(std::io::stderr) | ||
| .with_targets(true) | ||
| .with_bracketed_fields(true) | ||
| .with_indent_amount(2); |
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(These are stylistic options that can be tuned.)
ytmimi
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Definitely in favor of making this change. I've often struggled to keep track of things in the logs, so having a nested structure would help out a lot!
@jieyouxu I'll let you add this to the merge queue when you think it's ready since I see the DO NOT MERGE comment.
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Dropped the DO NOT MERGE commit, no other changes. |
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Motivation
We already use
tracingin rustfmt for various debug tracing. Right now, the traces are flat, and sometimes I find it hard to follow where debug traces are emitted, and what the call stack/tree is.Tracking issue: #7189
Implementation
Inspired by rustc's hierarchical traces, this PR introduces
tracing-tree(which is used by rustc) so we can introduce more structured debug tracing.Note that the hierarchy is only well-established by systematically introducing
#[instrument](or equivalent) to key functions so that we can emit tracing spans, and establish relationships between such tracing spans. Without systematic#[instrument]tracing spans, this PR is essentially a no-op.I will provide some example outputs as comments.
Follow-up work
This PR only sets up the initial infra. In follow-up PRs, I intend to:
#[instrument]to key functionsNotes for the reviewer
I intentionally included a DO NOT MERGE commit demonstrating theEDIT: now dropped.#[instrument]usages.Discussed previously in #t-rustfmt > tracing-tree?.