From 9f8d740ee22b9e70b6589856f6969cae9e8e3149 Mon Sep 17 00:00:00 2001
From: albertexye <albertexye@gmail.com>
Date: Mon, 1 Apr 2024 23:54:34 -0400
Subject: [PATCH] a ValueError is raised when argument 'start' is a negative
 integer

---
 src/pocketpy.cpp |  2 ++
 src/str.cpp      |  1 -
 tests/04_str.py  | 12 +++++++++++-
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/pocketpy.cpp b/src/pocketpy.cpp
index 27455846..37603f5b 100644
--- a/src/pocketpy.cpp
+++ b/src/pocketpy.cpp
@@ -627,6 +627,7 @@ void init_builtins(VM* _vm) {
         const Str& self = _CAST(Str&, args[0]);
         const Str& value = CAST(Str&, args[1]);
         int start = CAST(int, args[2]);
+        if (start < 0) vm->ValueError("argument 'start' can't be negative");
         int index = self.index(value, start);
         if(index < 0) vm->ValueError("substring not found");
         return VAR(index);
@@ -636,6 +637,7 @@ void init_builtins(VM* _vm) {
         const Str& self = _CAST(Str&, args[0]);
         const Str& value = CAST(Str&, args[1]);
         int start = CAST(int, args[2]);
+		if (start < 0) vm->ValueError("argument 'start' can't be negative");
         return VAR(self.index(value, start));
     });
 
diff --git a/src/str.cpp b/src/str.cpp
index 9965e6eb..b0308ffb 100644
--- a/src/str.cpp
+++ b/src/str.cpp
@@ -266,7 +266,6 @@ int utf8len(unsigned char c, bool suppress){
     }
 
     int Str::index(const Str& sub, int start) const {
-        if (start < 0) start = 0;
         auto p = std::search(data + start, data + size, sub.data, sub.data + sub.size);
         if(p == data + size) return -1;
         return p - data;
diff --git a/tests/04_str.py b/tests/04_str.py
index ed2e6d5e..c9c78eac 100644
--- a/tests/04_str.py
+++ b/tests/04_str.py
@@ -250,7 +250,17 @@ try:
 except ValueError:
     pass
 
+try:
+    a.index('1', -1)
+    exit(1)
+except ValueError:
+    pass
+
 assert a.find('1') == 0
 assert a.find('1', 1) == -1
-assert a.find('1', -1000000) == 0
 
+try:
+    a.find('1', -1)
+    exit(1)
+except ValueError:
+    pass