Re: [PATCH 2/2] checkout -m: refine autostash fallback

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Harald

On 25/07/2026 16:34, Harald Nordgren via GitGitGadget wrote:
> From: Harald Nordgren <haraldnordgren@gmail.com>
> 
> When unpack_trees() fails under "git checkout -m", only create an
> autostash and retry if there are tracked local changes.  Without such
> changes, the fallback cannot help and merely repeats the same failure.

Unfortunately to do that we have to look for local changes before the 
first call to unpack_trees() so we're trading an occasional 
inconvenience of an unnecessary stash and unstash for the cost of 
looking for local changes on every invocation of "git checkout -m". I 
don't think that is a good trade off, especially as there is no 
guarantee that stashing the local changes will make unpack_trees() 
succeed. To do this effectively would require refactoring unpack_trees() 
to write its error messages to a buffer and return an error flag that 
indicates all the errors that were encountered. We could then check if 
the only thing that prevented upack_trees() from succeeding was local 
changes to files and stash them, or if there are other errors print the 
error message. I suspect such a change is far from straight forward.

> Use the conflict result from apply_autostash_ref() to print a blank line
> before the branch-switch message, visually separating it from the
> conflict advice.


This change is very welcome and could happily be squashed into the first 
patch as it motivates the changes in it.

> diff --git a/t/t7201-co.sh b/t/t7201-co.sh
> index 0ddd1ad7aa..f9696dab36 100755
> --- a/t/t7201-co.sh
> +++ b/t/t7201-co.sh
> @@ -240,6 +240,14 @@ test_expect_success 'checkout -m creates a recoverable stash on conflict' '
>   	test_grep "git stash drop" actual &&
>   	test_grep "git stash pop" actual &&
>   	test_grep "The following paths have local changes" actual &&
> +	sed -n "/apply the local changes later/,/Switched to branch/p" \
> +		actual >separator.actual &&
> +	cat >separator.expect <<-EOF &&
> +	apply the local changes later by running "git stash pop".
> +
> +	Switched to branch ${SQ}side${SQ}
> +	EOF
> +	test_cmp separator.expect separator.actual &&

I wonder whether we should just bite the bullet and check what gets 
printed to the screen with test_cmp, rather than grepping for all these 
separate parts of the message. Is there something in the message that 
makes that difficult?

Thanks

Phillip

>   	git log -p -1 --format="%gs%n%B" -g --diff-merges=1 refs/stash >actual &&
>   	sed /^index/d actual >actual.trimmed &&
>   	cat >expect <<-EOF &&
> @@ -262,11 +270,18 @@ test_expect_success 'checkout -m creates a recoverable stash on conflict' '
>   	git reset --hard
>   '
>   
> -test_expect_success 'checkout -m which would overwrite untracked file' '
> +test_expect_success 'checkout -m only retries untracked-file failure with local changes' '
>   	git checkout -f --detach main &&
>   	test_commit another-file &&
>   	git checkout HEAD^ &&
>   	>another-file.t &&
> +	test_must_fail env GIT_TRACE2_EVENT="$(pwd)/trace" \
> +		git checkout -m @{-1} 2>err &&
> +	test_grep "untracked working tree files" err &&
> +	grep "\"region_enter\".*\"category\":\"index\",\"label\":\"refresh\"" \
> +		trace >refresh.events &&
> +	test_line_count = 1 refresh.events &&
> +
>   	fill 1 2 3 4 5 >one &&
>   	test_must_fail git checkout -m @{-1} 2>err &&
>   	q_to_tab >expect <<-\EOF &&