make the regression test more thorough; prepare for the pure V version

vlib/builtin/cfns_wrapper.c.v

@@ -79,7 +79,13 @@ mut:
 	real_sort_cb FnSortContextCB
 }
 
+
+// GLIBC:
+// void qsort_r(void *base, size_t nmemb, size_t size,
+//                   int (*compar)(const void *, const void *, void *),
+//                   void *arg);
 fn vqsort_context_pure_v(base voidptr, nmemb usize, size usize, sort_cb FnSortContextCB, context voidptr) {
+	C.qsort_r(base, nmemb, size, voidptr(sort_cb), context)
 }
 
 [inline; unsafe]

vlib/builtin/sort_with_compare_context_test.v

@@ -3,11 +3,16 @@ mut:
 	comparisons []string
 }
 
-fn test_sort_with_compare() {
-	mut a := ['hi', '1', '5', '3']
-	mut context := Context{}
-	a.sort_with_compare_context(fn (a &string, b &string, mut context Context) int {
-		context.comparisons << 'a: ${*a} | b: ${*b}'
+fn (c Context) str() string {
+	mut res := []string{}
+	for x in c.comparisons {
+		res << x
+	}
+	return '\n' + res.join('\n')
+}
+
+fn sort_cb(a &string, b &string, mut context Context) int {
+	context.comparisons << 'a: "${*a}" | b: "${*b}"'
 	if a < b {
 		return -1
 	}
@@ -15,15 +20,32 @@ fn test_sort_with_compare() {
 		return 1
 	}
 	return 0
-	}, context)
+}
+
+fn test_sort_with_compare() {
+	mut a := ['hi', '1', '5', '3']
+	mut context := Context{}
+	a.sort_with_compare_context(sort_cb, context)
 	dump(a)
 	dump(context)
 	assert a == ['1', '3', '5', 'hi']
 	assert context.comparisons == [
-		'a: hi | b: 1',
-		'a: 5 | b: 3',
-		'a: 1 | b: 3',
-		'a: hi | b: 3',
-		'a: hi | b: 5',
+		'a: "hi" | b: "1"',
+		'a: "5" | b: "3"',
+		'a: "1" | b: "3"',
+		'a: "hi" | b: "3"',
+		'a: "hi" | b: "5"',
+	]
+	//
+	mut already_sorted_context := Context{}
+	a.sort_with_compare_context(sort_cb, already_sorted_context)
+	dump(a)
+	dump(already_sorted_context)
+	assert context != already_sorted_context
+	assert already_sorted_context.comparisons == [
+		'a: "1" | b: "3"',
+		'a: "5" | b: "hi"',
+		'a: "1" | b: "5"',
+		'a: "3" | b: "5"',
 	]
 }