[PATCH v2] diff: update conflict handling for whitespace to issue a warning

From: Usman Akinyemi <usmanakinyemi202@gmail.com>

Modify the conflict resolution between tab-in-indent and indent-with-non-tab to issue a warning instead of terminating the operation with `die()`. Update the `git diff --check` test to capture and verify the warning message output.

Suggested-by: Phillip Wood <phillip.wood123@gmail.com>
Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>
---
    diff: update conflict handling for whitespace to issue a warning
    
    Changes from V1
    
     * Disable both WS_TAB_IN_INDENT and WS_INDENT_WITH_NON_TAB when both
       are set.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1828%2FUnique-Usman%2Fmaster-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1828/Unique-Usman/master-v2
Pull-Request: https://github.com/git/git/pull/1828

Range-diff vs v1:

 1:  dfb80a7ff2d ! 1:  8531e80811c diff: update conflict handling for whitespace to issue a warning
     @@ t/t4015-diff-whitespace.sh: test_expect_success 'ditto, but tabwidth=1 (must be
       	echo "foo ();" >x &&
      -	test_must_fail git diff --check
      +	git diff --check 2>error &&
     -+	test_grep "warning: cannot enforce both tab-in-indent and indent-with-non-tab, removing tab-in-indent" error
     ++	test_grep "warning: cannot enforce both tab-in-indent and indent-with-non-tab, disabling both" error
       '
       
       test_expect_success 'check tab-in-indent excluded from wildcard whitespace attribute' '
     @@ ws.c: unsigned parse_whitespace_rule(const char *string)
      -	if (rule & WS_TAB_IN_INDENT && rule & WS_INDENT_WITH_NON_TAB)
      -		die("cannot enforce both tab-in-indent and indent-with-non-tab");
      +	if (rule & WS_TAB_IN_INDENT && rule & WS_INDENT_WITH_NON_TAB) {
     -+		warning(_("cannot enforce both tab-in-indent and indent-with-non-tab, removing tab-in-indent"));
     ++		warning(_("cannot enforce both tab-in-indent and indent-with-non-tab, disabling both"));
      +		rule &= ~WS_TAB_IN_INDENT;
     ++		rule &= ~WS_INDENT_WITH_NON_TAB;
      +	}
       	return rule;
       }

 t/t4015-diff-whitespace.sh | 3 ++-
 ws.c                       | 8 ++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)