lib: add argument position support (`%m$`) to `sprintf()` and `printf()`

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

2 files changed, 38 insertions, 0 deletions

diff --git a/tests/custom/03_stdlib/27_sprintf b/tests/custom/03_stdlib/27_sprintf
index 3edcd48..e1a3c5d 100644
--- a/tests/custom/03_stdlib/27_sprintf
+++ b/tests/custom/03_stdlib/27_sprintf
@@ -548,3 +548,24 @@ Supplying a non-string format value will yield an empty string result.
 -- Expect stdout --
 ""
 -- End --
+
+
+Prefixing a format directive with `n$` will select the corresponding argument
+with 1 referring to the first argument. Missing or out-of range arguments will
+be treated as `null`.
+
+-- Testcase --
+{%
+	printf("%.J\n", [
+		sprintf("%2$s", "foo", "bar", "baz"),
+		sprintf("%10$s", "foo", "bar", "baz")
+	]);
+%}
+-- End --
+
+-- Expect stdout --
+[
+	"bar",
+	"(null)"
+]
+-- End --
diff --git a/tests/custom/03_stdlib/28_printf b/tests/custom/03_stdlib/28_printf
index a2a6d27..b4556b3 100644
--- a/tests/custom/03_stdlib/28_printf
+++ b/tests/custom/03_stdlib/28_printf
@@ -524,3 +524,20 @@ Supplying a non-string format value will yield an empty string result.
 
 -- Expect stdout --
 -- End --
+
+
+Prefixing a format directive with `n$` will select the corresponding argument
+with 1 referring to the first argument. Missing or out-of range arguments will
+be treated as `null`.
+
+-- Testcase --
+{%
+	printf("%2$s\n", "foo", "bar", "baz");
+	printf("%10$s\n", "foo", "bar", "baz");
+%}
+-- End --
+
+-- Expect stdout --
+bar
+(null)
+-- End --