[PATCH v3 1/1] quote: handle numm and empty strings in sq_quote_buf_pretty

["Garima Singh via GitGitGadget" <gitgitgadget@gmail.com>]

From: Garima Singh <garima.singh@microsoft.com>

The sq_quote_buf_pretty() function does not emit anything
when the incoming string is empty, but the function is to
accumulate command line arguments, properly quoted as
necessary, and the right way to add an argument that is an
empty string is to show it quoted, i.e. ''. We warn the caller
with the BUG macro is they pass in a NULL.

Reported by: Junio Hamano <gitster@pobox.com>
Signed-off-by: Garima Singh <garima.singh@microsoft.com>
---
 quote.c          | 10 ++++++++++
 t/t0014-alias.sh |  7 +++++++
 2 files changed, 17 insertions(+)

diff --git a/quote.c b/quote.c
index 7f2aa6faa4..f31ebf6c43 100644
--- a/quote.c
+++ b/quote.c
@@ -48,6 +48,16 @@ void sq_quote_buf_pretty(struct strbuf *dst, const char *src)
 	static const char ok_punct[] = "+,-./:=@_^";
 	const char *p;
 
+	/* In case of null tokens, warn the user of the BUG in their call. */
+	if (!src) 
+		BUG("Cannot append a NULL token to the buffer");
+	
+	/* Avoid dropping a zero-length token by adding '' */
+	if (!*src) {
+		strbuf_addstr(dst, "''");
+		return;
+	}
+
 	for (p = src; *p; p++) {
 		if (!isalpha(*p) && !isdigit(*p) && !strchr(ok_punct, *p)) {
 			sq_quote_buf(dst, src);
diff --git a/t/t0014-alias.sh b/t/t0014-alias.sh
index a070e645d7..ae316aa6fd 100755
--- a/t/t0014-alias.sh
+++ b/t/t0014-alias.sh
@@ -37,4 +37,11 @@ test_expect_success 'looping aliases - internal execution' '
 #	test_i18ngrep "^fatal: alias loop detected: expansion of" output
 #'
 
+test_expect_success 'run-command parses empty args properly, using sq_quote_buf_pretty' '
+    GIT_TRACE=1 git frotz a "" b " " c 2>&1 |
+    sed -ne "/run_command:/s/.*trace: run_command: //p" >actual &&
+    echo "git-frotz a '\'''\'' b '\'' '\'' c" >expect &&
+    test_cmp expect actual
+'
+
 test_done
-- 
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