Sync Meta Crates

Sync recent changes from hotpath → hotpath-meta, hotpath-macros → hotpath-macros-meta and hotpath-drain → hotpath-drain-meta.

The meta crates are copies of the main crates used to profile the profiler itself. They must stay in sync with the source crates.

Effective Approach

DO NOT copy entire files from hotpath to hotpath-meta and then sed-replace. This approach fails because the meta crates have many naming differences beyond simple hotpath:: → hotpath_meta:: substitution:

• Feature flags: hotpath → hotpath-meta, hotpath-alloc → hotpath-alloc-meta, hotpath-cpu → hotpath-cpu-meta, hotpath-cloud → hotpath-cloud-meta, hotpath-prometheus → hotpath-prometheus-meta, hotpath-mcp → hotpath-mcp-meta
• Crate imports: hotpath_macros → hotpath_macros_meta, hotpath_drain → hotpath_drain_meta
• Environment variables: HOTPATH_FOCUS → HOTPATH_META_FOCUS, HOTPATH_EXCLUDE_WRAPPER → HOTPATH_META_EXCLUDE_WRAPPER, HOTPATH_OUTPUT_PATH → HOTPATH_META_OUTPUT_PATH
• Self-instrumentation: lines like #[cfg_attr(feature = "hotpath-meta", hotpath_meta::measure_all)] exist in hotpath but must NOT exist in hotpath-meta
• hotpath-drain-meta is the simplest mirror: it has no features and no dependencies, so syncing hotpath-drain means applying the diff and dropping the #[cfg_attr(feature = "hotpath-meta", hotpath_meta::measure(...))] lines. Nothing else is renamed - there is no hotpath-drain-meta feature flag.

Instead, apply diffs to the existing meta files:

1. Get the actual diff for each changed file: git diff HEAD~N..HEAD -- crates/hotpath/src/path/to/file.rs
2. Read the corresponding meta file
3. Apply the equivalent semantic changes, preserving all meta-specific naming

Steps

1. Check the last N commits (default 1, user can specify more) for changes to crates/hotpath/, crates/hotpath-macros/ and crates/hotpath-drain/:

git log --oneline -N
git diff HEAD~N..HEAD --name-only -- crates/hotpath/src/ crates/hotpath-macros/src/ crates/hotpath-drain/src/

2. For each changed file, get the source diff:

git diff HEAD~N..HEAD -- crates/hotpath/src/path/to/file.rs
git diff HEAD~N..HEAD -- crates/hotpath-drain/src/lib.rs

3. Read the corresponding meta file and apply the equivalent changes using Edit tool. The meta files are at:

   • crates/hotpath/src/** → crates/hotpath-meta/src/**
   • crates/hotpath-macros/src/** → crates/hotpath-macros-meta/src/**
   • crates/hotpath-drain/src/** → crates/hotpath-drain-meta/src/**

4. Verify the meta crates compile:

cargo check -p hotpath-drain-meta
cargo check -p hotpath-meta
cargo check -p hotpath-meta --features hotpath-meta
cargo check -p hotpath-macros-meta --features hotpath-meta
cargo check -p hotpath-meta --features hotpath-meta,hotpath-alloc-meta
cargo check -p hotpath-meta --features hotpath-meta,hotpath-alloc-meta,hotpath-prometheus-meta

The no-feature check covers the lib_off path. Every *-meta sub-feature (hotpath-alloc-meta, hotpath-cpu-meta, hotpath-cloud-meta, hotpath-prometheus-meta, hotpath-mcp-meta) requires hotpath-meta and hits a compile_error! on its own, so always combine them with hotpath-meta. Add hotpath-cloud-meta / hotpath-mcp-meta / hotpath-cpu-meta to the last command when the synced files touch those subsystems.

5. Report a summary of what was synced.

Rules

• Only sync src/ files, never Cargo.toml or other config files. examples/ and tests/ (including the miri test in hotpath-drain) are not mirrored either.
• If no changes were made to the source crates in the specified commits, report that and exit.
• NEVER copy entire files and do bulk find-and-replace. Always apply diffs to existing meta files.
• Preserve ALL meta-specific naming conventions (feature flags, env vars, crate names, self-instrumentation removal).
• Lines with #[cfg_attr(feature = "hotpath-meta", hotpath_meta::...)] in hotpath are self-instrumentation and must NOT be copied to meta crates.
• The meta feature flags are hotpath-meta, hotpath-alloc-meta, hotpath-cpu-meta, hotpath-cloud-meta, hotpath-prometheus-meta, hotpath-mcp-meta (NOT hotpath, hotpath-alloc, ...). There is no hotpath-off-meta; the disabled path is the no-feature build.