Re: [PATCH v2] test_cmp: diagnose incorrect arguments

[Taylor Blau <me@ttaylorr.com>]

On Sun, Aug 09, 2020 at 01:42:09PM -0400, Eric Sunshine wrote:
> Under normal circumstances, if a test author misspells a filename passed
> to test_cmp(), the error is quickly discovered when the test fails
> unexpectedly due to test_cmp() being unable to find the file. However,
> if the test is expected to fail, as with test_expect_failure(), a
> misspelled filename as argument to test_cmp() will go unnoticed since
> the test will indeed fail, but for the wrong reason. Make it easier for
> test authors to discover such problems early by sanity-checking the
> arguments to test_cmp(). To avoid penalizing all clients of test_cmp()
> in the general case, only check for missing files if the comparison
> fails.
>
> While at it, make test_cmp_bin() sanity-check its arguments, as well.
>
> Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
> ---
>
> Notes:
>     This is a re-roll of [1] which was motivated by seeing Elijah fix[2]
>     several cases of bogus test_cmp() calls which perhaps could have
>     been detected earlier.
>
>     Changes since v1:
>
>     * take into account that some callers pass "-" (meaning standard
>       input) as an argument to test_cmp() (pointed out privately by
>       Junio)
>
>     * show the name of the missing file rather than a placeholder
>       (Shourya[3])
>
>     [1]: https://lore.kernel.org/git/20200809060810.31370-1-sunshine@sunshineco.com/
>     [2]: https://lore.kernel.org/git/7f408b7d4069403b969d334f4940ebf87f1dc797.1596906081.git.gitgitgadget@gmail.com/
>     [3]: https://lore.kernel.org/git/20200809083227.GA11219@konoha/
>
> Interdiff against v1:
>   diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
>   index 8d77deebd2..a12d6a3fc9 100644
>   --- a/t/test-lib-functions.sh
>   +++ b/t/test-lib-functions.sh
>   @@ -955,8 +955,8 @@ test_cmp() {
>    	test $# -eq 2 || BUG "test_cmp requires two arguments"
>    	if ! eval "$GIT_TEST_CMP" '"$@"'
>    	then
>   -		test -e "$1" || BUG "test_cmp 'expect' file missing"
>   -		test -e "$2" || BUG "test_cmp 'actual' file missing"
>   +		test "x$1" = x- || test -e "$1" || BUG "test_cmp '$1' missing"
>   +		test "x$2" = x- || test -e "$2" || BUG "test_cmp '$2' missing"
>    		return 1
>    	fi
>    }
>   @@ -990,8 +990,8 @@ test_cmp_bin() {
>    	test $# -eq 2 || BUG "test_cmp_bin requires two arguments"
>    	if ! cmp "$@"
>    	then
>   -		test -e "$1" || BUG "test_cmp_bin 'expect' file missing"
>   -		test -e "$2" || BUG "test_cmp_bin 'actual' file missing"
>   +		test "x$1" = x- || test -e "$1" || BUG "test_cmp_bin '$1' missing"
>   +		test "x$2" = x- || test -e "$2" || BUG "test_cmp_bin '$2' missing"
>    		return 1
>    	fi
>    }
>
>  t/test-lib-functions.sh | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
> index b791933ffd..a12d6a3fc9 100644
> --- a/t/test-lib-functions.sh
> +++ b/t/test-lib-functions.sh
> @@ -952,7 +952,13 @@ test_expect_code () {
>  # - not all diff versions understand "-u"
>
>  test_cmp() {
> -	eval "$GIT_TEST_CMP" '"$@"'
> +	test $# -eq 2 || BUG "test_cmp requires two arguments"
> +	if ! eval "$GIT_TEST_CMP" '"$@"'
> +	then
> +		test "x$1" = x- || test -e "$1" || BUG "test_cmp '$1' missing"
> +		test "x$2" = x- || test -e "$2" || BUG "test_cmp '$2' missing"

Not related to your patch, but I've seen this style of "x$1" in a few
places in test-lib-functions.sh. Why can't this be written as 'test "$1"
= -'?

> +		return 1
> +	fi
>  }
>
>  # Check that the given config key has the expected value.
> @@ -981,7 +987,13 @@ test_cmp_config() {
>  # test_cmp_bin - helper to compare binary files
>
>  test_cmp_bin() {
> -	cmp "$@"
> +	test $# -eq 2 || BUG "test_cmp_bin requires two arguments"
> +	if ! cmp "$@"
> +	then
> +		test "x$1" = x- || test -e "$1" || BUG "test_cmp_bin '$1' missing"
> +		test "x$2" = x- || test -e "$2" || BUG "test_cmp_bin '$2' missing"
> +		return 1
> +	fi
>  }
>
>  # Use this instead of test_cmp to compare files that contain expected and
> --
> 2.28.0.220.ged08abb693
>
Thanks,
Taylor