There was a discussion of problematic directory/file conflicts with virtual merge bases on the mailing list years ago at https://public-inbox.org/git/AANLkTimwUQafGDrjxWrfU9uY1uKoFLJhxYs=vssOPqdf@xxxxxxxxxxxxxx/ Part of these corresponding tests made it into this testsuite. However, the more problematic one didn't. And there are others that showcase the problems even more. Add a very lengthy explanation, some of it from that email, describing the tradeoffs in picking a recursive merge-base when you're dealing with an add/add directory/file conflict. The solution picked years ago is relatively good, but there is the potential to do even better, assuming we're willing to pay a certain performance cost. Signed-off-by: Elijah Newren <newren@xxxxxxxxx> --- t/t6036-recursive-corner-cases.sh | 256 +++++++++++++++++++++++------- 1 file changed, 201 insertions(+), 55 deletions(-) diff --git a/t/t6036-recursive-corner-cases.sh b/t/t6036-recursive-corner-cases.sh index b5621303d..74e5920bc 100755 --- a/t/t6036-recursive-corner-cases.sh +++ b/t/t6036-recursive-corner-cases.sh @@ -345,40 +345,97 @@ test_expect_success 'git detects conflict merging criss-cross+modify/delete, rev ) ' +# SORRY FOR THE SUPER LONG DESCRIPTION, BUT THIS NEXT ONE IS HAIRY # # criss-cross + d/f conflict via add/add: # Commit A: Neither file 'a' nor directory 'a/' exists. # Commit B: Introduce 'a' # Commit C: Introduce 'a/file' -# Commit D: Merge B & C, keeping 'a' and deleting 'a/' -# -# Two different later cases: +# Commit D1: Merge B & C, keeping 'a' and deleting 'a/' # Commit E1: Merge B & C, deleting 'a' but keeping 'a/file' -# Commit E2: Merge B & C, deleting 'a' but keeping a slightly modified 'a/file' # -# B D +# B D1 or D2 # o---o # / \ / \ # A o X ? F # \ / \ / # o---o -# C E1 or E2 -# -# Merging D & E1 requires we first create a virtual merge base X from -# merging A & B in memory. Now, if X could keep both 'a' and 'a/file' in -# the index, then the merge of D & E1 could be resolved cleanly with both -# 'a' and 'a/file' removed. Since git does not currently allow creating -# such a tree, the best we can do is have X contain both 'a~<unique>' and -# 'a/file' resulting in the merge of D and E1 having a rename/delete -# conflict for 'a'. (Although this merge appears to be unsolvable with git -# currently, git could do a lot better than it currently does with these -# d/f conflicts, which is the purpose of this test.) -# -# Merge of D & E2 has similar issues for path 'a', but should always result -# in a modify/delete conflict for path 'a/file'. -# -# We run each merge in both directions, to check for directional issues -# with D/F conflict handling. +# C E1 or E2 or E3 +# +# I'll describe D2, E2, & E3 (which are alternatives for D1 & E1) more below... +# +# Merging D1 & E1 requires we first create a virtual merge base X from +# merging A & B in memory. There are several possibilities for the merge-base: +# 1: Keep both 'a' and 'a/file' (assuming crazy filesystem allowing a tree +# with a directory and file at same path): results in merge of D1 & E1 +# being clean with both files deleted. Bad (no conflict detected). +# 2: Keep 'a' but not 'a/file': Merging D1 & E1 is clean and matches E1. Bad. +# 3: Keep 'a/file' but not 'a': Merging D1 & E1 is clean and matches D1. Bad. +# 4: Keep neither file: Merging D1 & E1 reports the D/F add/add conflict. +# +# So 4 sounds good for this case, but if we were to merge D1 & E3, where E3 +# is defined as: +# Commit E3: Merge B & C, keeping modified a, and deleting a/ +# then we'd get an add/add conflict for 'a', which seems suboptimal. A little +# creativity leads us to an alternate choice: +# 5: Keep 'a' as 'a~$UNIQUE' and a/file; results: +# Merge D1 & E1: rename/delete conflict for 'a'; a/file silently deleted +# Merge D1 & E3 is clean, as expected. +# +# So choice 5 at least provides some kind of conflict for the original case, +# and can merge cleanly as expected with D1 and E3. It also made things just +# slightly funny for merging D1 and e$, where E4 is defined as: +# Commit E4: Merge B & C, modifying 'a' and renaming to 'a2', and deleting 'a/' +# in this case, we'll get a rename/rename(1to2) conflict because a~$UNIQUE +# gets renamed to 'a' in D1 and to 'a2' in E4. But that's better than having +# two files (both 'a' and 'a2') sitting around without the user being notified +# that we could detect they were related and need to be merged. Also, choice +# 5 makes the handling of 'a/file' seem suboptimal. What if we were to merge +# D2 and E4, where D2 is: +# Commit D2: Merge B & C, renaming 'a'->'a2', keeping 'a/file' +# This would result in a clean merge with 'a2' having three-way merged +# contents (good), and deleting 'a/' (bad) -- it doesn't detect the +# conflict in how the different sides treated a/file differently. +# Continuing down the creative route: +# 6: Keep 'a' as 'a~$UNIQUE1' and keep 'a/' as 'a~$UNIQUE2/'; results: +# Merge D1 & E1: rename/delete conflict for 'a' and each path under 'a/'. +# Merge D1 & E3: clean, as expected. +# Merge D1 & E4: rename/rename(1to2) conflict on 'a' vs 'a2'. +# Merge D2 & E4: clean for 'a2', rename/delete for a/file +# +# Choice 6 could cause rename detection to take longer (providing more targets +# that need to be searched). Also, the conflict message for each path under +# 'a/' might be annoying unless we can detect it at the directory level, print +# it once, and then suppress it for individual filepaths underneath. +# +# +# As of time of writing, git uses choice 5. Directory rename detection and +# rename detection performance improvements might make choice 6 a desirable +# improvement. But we can at least document where we fall short for now... +# +# +# Historically, this testcase also used: +# Commit E2: Merge B & C, deleting 'a' but keeping slightly modified 'a/file' +# The merge of D1 & E2 is very similar to D1 & E1 -- it has similar issues for +# path 'a', but should always result in a modify/delete conflict for path +# 'a/file'. These tests ran the two merges +# D1 & E1 +# D1 & E2 +# in both directions, to check for directional issues with D/F conflict +# handling. Later we added +# D1 & E3 +# D1 & E4 +# D2 & E4 +# for good measure, though we only ran those one way because we had pretty +# good confidence in merge-recursive's directional handling of D/F issues. +# +# Just to summarize all the intermediate merge commits: +# Commit D1: Merge B & C, keeping a and deleting a/ +# Commit D2: Merge B & C, renaming a->a2, keeping a/file +# Commit E1: Merge B & C, deleting a but keeping a/file +# Commit E2: Merge B & C, deleting a but keeping slightly modified a/file +# Commit E3: Merge B & C, keeping modified a, and deleting a/ +# Commit E4: Merge B & C, modifying 'a' and renaming to 'a2', and deleting 'a/' # test_expect_success 'setup differently handled merges of directory/file conflict' ' @@ -395,56 +452,70 @@ test_expect_success 'setup differently handled merges of directory/file conflict git branch B && git checkout -b C && mkdir a && - echo 10 >a/file && + test_write_lines a b c d e f g >a/file && git add a/file && test_tick && git commit -m C && git checkout B && - echo 5 >a && + test_write_lines 1 2 3 4 5 6 7 >a && git add a && test_tick && git commit -m B && git checkout B^0 && - test_must_fail git merge C && - git clean -f && - rm -rf a/ && - echo 5 >a && - git add a && - test_tick && - git commit -m D && - git tag D && + git merge -s ours -m D1 C^0 && + git tag D1 && + + git checkout B^0 && + test_must_fail git merge C^0 && + git clean -fd && + git rm -rf a/ && + git rm a && + git cat-file -p B:a >a2 && + git add a2 && + git commit -m D2 && + git tag D2 && git checkout C^0 && - test_must_fail git merge B && - git clean -f && - git rm --cached a && - echo 10 >a/file && - git add a/file && - test_tick && - git commit -m E1 && + git merge -s ours -m E1 B^0 && git tag E1 && git checkout C^0 && - test_must_fail git merge B && - git clean -f && - git rm --cached a && - printf "10\n11\n" >a/file && + git merge -s ours -m E2 B^0 && + test_write_lines a b c d e f g h >a/file && git add a/file && - test_tick && - git commit -m E2 && - git tag E2 + git commit --amend -C HEAD && + git tag E2 && + + git checkout C^0 && + test_must_fail git merge B^0 && + git clean -fd && + git rm -rf a/ && + test_write_lines 1 2 3 4 5 6 7 8 >a && + git add a && + git commit -m E3 && + git tag E3 + + git checkout C^0 && + test_must_fail git merge B^0 && + git clean -fd && + git rm -rf a/ && + git rm a && + test_write_lines 1 2 3 4 5 6 7 8 >a2 && + git add a2 && + git commit -m E4 && + git tag E4 ) ' -test_expect_success 'merge of D & E1 fails but has appropriate contents' ' +test_expect_success 'merge of D1 & E1 fails but has appropriate contents' ' test_when_finished "git -C directory-file reset --hard" && test_when_finished "git -C directory-file clean -fdqx" && ( cd directory-file && - git checkout D^0 && + git checkout D1^0 && test_must_fail git merge -s recursive E1^0 && @@ -463,7 +534,7 @@ test_expect_success 'merge of D & E1 fails but has appropriate contents' ' ) ' -test_expect_success 'merge of E1 & D fails but has appropriate contents' ' +test_expect_success 'merge of E1 & D1 fails but has appropriate contents' ' test_when_finished "git -C directory-file reset --hard" && test_when_finished "git -C directory-file clean -fdqx" && ( @@ -471,7 +542,7 @@ test_expect_success 'merge of E1 & D fails but has appropriate contents' ' git checkout E1^0 && - test_must_fail git merge -s recursive D^0 && + test_must_fail git merge -s recursive D1^0 && git ls-files -s >out && test_line_count = 2 out && @@ -488,13 +559,13 @@ test_expect_success 'merge of E1 & D fails but has appropriate contents' ' ) ' -test_expect_success 'merge of D & E2 fails but has appropriate contents' ' +test_expect_success 'merge of D1 & E2 fails but has appropriate contents' ' test_when_finished "git -C directory-file reset --hard" && test_when_finished "git -C directory-file clean -fdqx" && ( cd directory-file && - git checkout D^0 && + git checkout D1^0 && test_must_fail git merge -s recursive E2^0 && @@ -515,7 +586,7 @@ test_expect_success 'merge of D & E2 fails but has appropriate contents' ' ) ' -test_expect_success 'merge of E2 & D fails but has appropriate contents' ' +test_expect_success 'merge of E2 & D1 fails but has appropriate contents' ' test_when_finished "git -C directory-file reset --hard" && test_when_finished "git -C directory-file clean -fdqx" && ( @@ -523,7 +594,7 @@ test_expect_success 'merge of E2 & D fails but has appropriate contents' ' git checkout E2^0 && - test_must_fail git merge -s recursive D^0 && + test_must_fail git merge -s recursive D1^0 && git ls-files -s >out && test_line_count = 4 out && @@ -538,7 +609,82 @@ test_expect_success 'merge of E2 & D fails but has appropriate contents' ' :3:a :2:a/file :1:a/file :0:ignore-me && test_cmp expect actual - test_path_is_file a~D^0 + test_path_is_file a~D1^0 + ) +' + +test_expect_success 'merge of D1 & E3 succeeds' ' + test_when_finished "git -C directory-file reset --hard" && + test_when_finished "git -C directory-file clean -fdqx" && + ( + cd directory-file && + + git checkout D1^0 && + + git merge -s recursive E3^0 && + + git ls-files -s >out && + test_line_count = 2 out && + git ls-files -u >out && + test_line_count = 0 out && + git ls-files -o >out && + test_line_count = 1 out && + + git rev-parse >expect \ + A:ignore-me E3:a && + git rev-parse >actual \ + :0:ignore-me :0:a && + test_cmp expect actual + ) +' + +test_expect_success 'merge of D1 & E4 notifies user a and a2 are related' ' + test_when_finished "git -C directory-file reset --hard" && + test_when_finished "git -C directory-file clean -fdqx" && + ( + cd directory-file && + + git checkout D1^0 && + + test_must_fail git merge -s recursive E4^0 && + + git ls-files -s >out && + test_line_count = 4 out && + git ls-files -u >out && + test_line_count = 3 out && + git ls-files -o >out && + test_line_count = 1 out && + + git rev-parse >expect \ + A:ignore-me B:a D1:a E4:a2 && + git rev-parse >actual \ + :0:ignore-me :1:a~Temporary\ merge\ branch\ 2 :2:a :3:a2 && + test_cmp expect actual + ) +' + +test_expect_failure 'merge of D2 & E4 merges a2s & reports conflict for a/file' ' + test_when_finished "git -C directory-file reset --hard" && + test_when_finished "git -C directory-file clean -fdqx" && + ( + cd directory-file && + + git checkout D2^0 && + + test_must_fail git merge -s recursive E4^0 && + + git ls-files -s >out && + test_line_count = 3 out && + git ls-files -u >out && + test_line_count = 1 out && + git ls-files -o >out && + test_line_count = 1 out && + + git rev-parse >expect \ + A:ignore-me E4:a2 D2:a/file && + git rev-parse >actual \ + :0:ignore-me :0:a2 :2:a/file && + test_cmp expect actual ) ' -- 2.18.0.131.g7487c9a82.dirty
