Code History

Figure out if code is still used and whether it's safe to remove. Pick whichever techniques below are useful -- you don't need all of them.

Techniques

Search for callers with grep -rn 'symbol' --include='*.rs' across the whole repo. Classify hits as definition, test, re-export, or real caller. Zero real callers usually means dead. Also check pub use re-exports -- if nothing imports the re-export, it's still dead.

Find the introducing commit with git log --all --oneline --diff-filter=A -S 'symbol' -- '*.rs'. Then git show <commit> --stat to see what else was part of that change.

Trace the lifecycle with git log --all --oneline -S 'symbol' -- '*.rs' to see every commit that added or removed lines with the symbol. Look for commits that deleted callers without deleting the code they called -- that's usually how dead code happens.

Blame with git blame path/to/file.rs -L 100,120. If a function hasn't been touched since the original commit but surrounding code has evolved, it's probably orphaned.

Check transitive usage -- a symbol with zero direct callers might still be reachable through pub use re-exports or trait impls (impl Trait for). If nothing outside the crate uses the re-export, it's dead.

Decision framework

Output format

1. What it does -- one sentence.
2. Who introduced it and why -- commit hash, date, original purpose.
3. What happened -- commit(s) that made it dead or reduced callers.
4. Current state -- real callers, test-only callers, re-exports.
5. Recommendation -- remove, inline, or keep. If remove, list all locations.

Git commands reference

git log --all --oneline --diff-filter=A -S 'symbol' -- '*.rs'  # first appearance
git log --all --oneline -S 'symbol' -- '*.rs'                   # all touches
git log --all --oneline -20 -- path/to/file.rs                  # file history
git show <commit>:path/to/file.rs                               # file at commit
git show <commit> -- path/to/file.rs                            # diff for one file
git show <commit> --stat                                        # files changed
git blame path/to/file.rs -L 100,120                            # blame range
git blame -w path/to/file.rs -L 100,120                         # blame ignoring whitespace
git log -1 -S 'deleted_line' -- path/to/file.rs                 # find deletion
git log --all --merges --oneline -S 'symbol'                    # merge commits