From 876834ff291cc03f639e35b2a0412e79a72ae47c Mon Sep 17 00:00:00 2001
From: James Shubin <james@shubin.ca>
Date: Sat, 24 May 2025 21:03:19 -0400
Subject: [PATCH] lang: core: fmt: Catch printf edge case

---
 lang/core/fmt/printf.go                                      | 3 +++
 lang/interpret_test/TestAstFunc2/printfunificationerr0.txtar | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/lang/core/fmt/printf.go b/lang/core/fmt/printf.go
index 9bb6ad3f..11fe7261 100644
--- a/lang/core/fmt/printf.go
+++ b/lang/core/fmt/printf.go
@@ -169,6 +169,9 @@ func (obj *PrintfFunc) FuncInfer(partialType *types.Type, partialValues []types.
 		if err != nil {
 			return nil, nil, errwrap.Wrapf(err, "could not parse format string")
 		}
+		if a, l := len(typList)-1, len(formatList); a != l {
+			return nil, nil, fmt.Errorf("number of args (%d) doesn't match format string verb count (%d)", a, l)
+		}
 		for i, x := range typList {
 			if i == 0 { // format string
 				continue
diff --git a/lang/interpret_test/TestAstFunc2/printfunificationerr0.txtar b/lang/interpret_test/TestAstFunc2/printfunificationerr0.txtar
index 61f4bd55..ff0f5b94 100644
--- a/lang/interpret_test/TestAstFunc2/printfunificationerr0.txtar
+++ b/lang/interpret_test/TestAstFunc2/printfunificationerr0.txtar
@@ -2,4 +2,4 @@
 import "fmt"
 test fmt.printf("%d%d", 42) {} # should not pass, missing second int
 -- OUTPUT --
-# err: errUnify: type error: str != list: /main.mcl @ 2:1-2:30
+# err: errUnify: func `printf` infer error: number of args (1) doesn't match format string verb count (2)