kunit: make KUNIT_EXPECT_STREQ() quote values, don't print literals

Before:
> Expected str == "world", but
> str == hello
> "world" == world

After:
> Expected str == "world", but
> str == "hello"
<we don't need to tell the user that "world" == "world">

Note: like the literal ellision for integers, this doesn't handle the
case of
KUNIT_EXPECT_STREQ(test, "hello", "world")
since we don't expect it to realistically happen in checked in tests.
(If you really wanted a test to fail, KUNIT_FAIL("msg") exists)

In that case, you'd get:
> Expected "hello" == "world", but
<output for next failure>

Signed-off-by: Daniel Latypov <[e-mail]>
Reviewed-by: Brendan Higgins <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

lib/kunit/assert.c

···
 }
 EXPORT_SYMBOL_GPL(kunit_binary_ptr_assert_format);
 
+/* Checks if KUNIT_EXPECT_STREQ() args were string literals.
+ * Note: `text` will have ""s where as `value` will not.
+ */
+static bool is_str_literal(const char *text, const char *value)
+{
+	int len;
+
+	len = strlen(text);
+	if (len < 2)
+		return false;
+	if (text[0] != '\"' || text[len - 1] != '\"')
+		return false;
+
+	return strncmp(text + 1, value, len - 2) == 0;
+}
+
 void kunit_binary_str_assert_format(const struct kunit_assert *assert,
 				    struct string_stream *stream)
 {
···
 			  binary_assert->left_text,
 			  binary_assert->operation,
 			  binary_assert->right_text);
-	string_stream_add(stream, KUNIT_SUBSUBTEST_INDENT "%s == %s\n",
-			  binary_assert->left_text,
-			  binary_assert->left_value);
-	string_stream_add(stream, KUNIT_SUBSUBTEST_INDENT "%s == %s",
-			  binary_assert->right_text,
-			  binary_assert->right_value);
+	if (!is_str_literal(binary_assert->left_text, binary_assert->left_value))
+		string_stream_add(stream, KUNIT_SUBSUBTEST_INDENT "%s == \"%s\"\n",
+				  binary_assert->left_text,
+				  binary_assert->left_value);
+	if (!is_str_literal(binary_assert->right_text, binary_assert->right_value))
+		string_stream_add(stream, KUNIT_SUBSUBTEST_INDENT "%s == \"%s\"",
+				  binary_assert->right_text,
+				  binary_assert->right_value);
 	kunit_assert_print_msg(assert, stream);
 }
 EXPORT_SYMBOL_GPL(kunit_binary_str_assert_format);