Error while formatting an error type | Zig Programming Language | Page 1

tardy pendant Jan 7, 2023, 1:31 PM

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The following code:

    decode24(out.slice(), str) catch |err| {
        debug("error: {}", .{err});
        unreachable;
    };

Generates the following compile error:

/usr/lib/zig/std/mem.zig:205:17: error: unable to evaluate comptime expression
        dest[i] = s;
        ~~~~~~~~^~~
/usr/lib/zig/std/mem.zig:205:13: note: operation is runtime due to this operand
        dest[i] = s;
        ~~~~^~~
/usr/lib/zig/std/io/fixed_buffer_stream.zig:70:21: note: called from here
            mem.copy(u8, self.buffer[self.pos .. self.pos + n], bytes[0..n]);
            ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/zig/std/io/writer.zig:17:27: note: called from here
            return writeFn(self.context, bytes);
                   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~
/usr/lib/zig/std/io/writer.zig:23:40: note: called from here
                index += try self.write(bytes[index..]);
                             ~~~~~~~~~~^~~~~~~~~~~~~~~~
/usr/lib/zig/std/fmt.zig:121:32: note: called from here
            try writer.writeAll(fmt[start_index..end_index]);
                ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/zig/std/fmt.zig:1954:15: note: called from here
    try format(fbs.writer(), fmt, args);
        ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
/home/kuon/pbg/zkfs-sdk/js/src/common/log.zig:16:31: note: called from here
    var buf = std.fmt.bufPrint(&log_buf, format ++ "\r\n", args) catch {
              ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/zig/std/log.zig:125:22: note: called from here
    std.options.logFn(message_level, scope, format, args);
    ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/zig/std/log.zig:203:16: note: called from here
            log(.debug, scope, format, args);
            ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/client.zig:17:14: note: called from here
        debug("error: {}", .{err});
        ~~~~~^~~~~~~~~~~~~~~~~~~~~
src/client.zig:24:24: note: called from here

Am I doing something wrong or is it a zig bug?

formal beacon Jan 7, 2023, 1:39 PM

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Sounds like you're trying to do this at a comptime scope

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Also unreachable is most likely not what you want here. It's UB in non-safe modes.

tardy pendant Jan 7, 2023, 1:46 PM

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yes it's just to test

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we cannot print error at comptime for debugging?

formal beacon Jan 7, 2023, 1:48 PM

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No, you cannot use syscalls during comptime

tardy pendant Jan 7, 2023, 1:48 PM

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I should use @compileError to inspect an error at compile time?

formal beacon Jan 7, 2023, 1:49 PM

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You can use @compileLog as that doesn't stop compilation at the first occurance it hits. It does however fail compilation at the end.

tardy pendant Jan 7, 2023, 1:50 PM

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ok thanks

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the error message could be improved 😄

formal beacon Jan 7, 2023, 1:50 PM

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Sure

tardy pendant Jan 7, 2023, 1:51 PM

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do you think it is worth making an issue if there is not already one?

formal beacon Jan 7, 2023, 1:53 PM

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Can’t decide that for you. To me the error message is clear as day, but that’s probably because of experience. There’s an issue template exactly for error messages, so it’s probably worth it if there isn’t one.

tardy pendant Jan 7, 2023, 1:55 PM

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yeah now that I realize what cause it, it is clear, but having a small hint "you cannot make syscall at comptime, use @compileLog" would have saved me some time.

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I'll make an issue

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thanks a lot for your help

#Error while formatting an error type