translate-c doesn't cast signed array index

[travisstaloch]

currently (0.5.0+b3dbdf2ad) this

void foo() {
  int a[10], i = 0;
  a[i] = 0;
}

gets translated to:

pub export fn foo() void {
    var a: [10]c_int = undefined;
    var i: c_int = 0;
    a[i] = 0;
}

which results in the zig compilation error:

error: expected type 'usize', found 'c_int'
    a[i] = 0;
      ^

I'm not sure exactly what type this should be cast to, but here is one working option, casting to c_uint.

diff --git a/test/translate_c.zig b/test/translate_c.zig
index 34d6bb3a0..73e14ee5a 100644
--- a/test/translate_c.zig
+++ b/test/translate_c.zig
@@ -1300,6 +1300,19 @@ pub fn addCases(cases: *tests.TranslateCContext) void {
         \\}
     });
 
+    cases.add("cast signed array index to unsigned",
+        \\void foo() {
+        \\  int a[10], i = 0;
+        \\  a[i] = 0;
+        \\}
+    , &[_][]const u8{
+        \\pub export fn foo() void {
+        \\    var a: [10]c_int = undefined;
+        \\    var i: c_int = 0;
+        \\    a[@intCast(c_uint, i)] = 0;
+        \\}
+    });
+
     cases.add("for loops",
         \\int foo() {
         \\    for (int i = 2, b = 4; i + 2; i = 2) {

[LemonBoy]

This should be easy to fix :)
Have a look at transArrayAccess in translate_c.zig, the idea here is to convert whatever the index type is to usize.

[travisstaloch]

Thanks. I'm working on it now and might actually be close 👍 ...

[travisstaloch]

I did a thing!

========= Expected this output: ================
pub export var array: [100]c_int = .{0} ** 100;
pub export fn foo(arg_index: c_int) c_int {
    var index = arg_index;
    return array[index];
}
========= But found: ===========================
pub export var array: [100]c_int = .{0} ** 100;
pub export fn foo(arg_index: c_int) c_int {
    var index = arg_index;
    return array[@intCast(c_uint, index)];
}

Now to update the failing tests :)