better error message when building an exe, not linking libc, and exporting libc main

[dimenus]

Seems to fail on x86_64, i386 in both GNU and MSVC.

MRE code:

const c = @cImport(@cInclude("stdio.h"));
export fn entry() void {
    c.printf("hello, world!\n");
}

compiler call:
zig build-exe load.zig

output:
C:\msys64\home\ryan\load.zig:3:6: error: no member named 'printf' in '(C import)' c.printf("hello\n");

[andrewrk]

Were you looking at ziglang.org? I updated the example there to match what was in the examples/ folder. Tell me if that didn't fix it.

[andrewrk]

We'll be able to support this smaller example on windows, but first we have to solve #515.

[dimenus]

Yes, I was. Will refresh.

As for the sample from examples/ bootstrap.zig appears to get in the way:

F:\code\tools\zig\build-w64-debug\lib\zig\std\special\bootstrap.zig:66:8: error: exported symbol collision: 'main'
export fn main(c_argc: i32, c_argv: &&u8, c_envp: &?&u8) -> i32 {
       ^
F:\code\tools\zig\build-w64-debug\load.zig:10:8: note: other symbol is here
export fn main(argc: c_int, argv: &&u8) -> c_int {
       ^
F:\code\tools\zig\build-w64-debug\lib\zig\std\special\bootstrap.zig:41:34: error: expected type '?fn() -> %void', found 'extern fn(c_int, &&u8) -> c_int'
    std.debug.user_main_fn = root.main;
                                 ^
F:\code\tools\zig\build-w64-debug\lib\zig\std\special\bootstrap.zig:42:14: error: expected 2 arguments, found 0
    root.main() %% std.os.windows.ExitProcess(1);
             ^
F:\code\tools\zig\build-w64-debug\load.zig:10:8: note: declared here
export fn main(argc: c_int, argv: &&u8) -> c_int {

[andrewrk]

I think you need --library c.

This error message could be better, for example we could give the error expected pub main() -> %void, found export fn main...

[andrewrk]

Note that you can also use the normal pub fn main() -> %void when you link libc.

[dimenus]

Ok, getting Unable to determine msvc lib path. now but that's to be expected since I'm using VS 2017 w/ the install on a non-standard path. I can look at making that part more robust on my own ( and will submit a pull if/when I come up with something). Thanks for the quick response!

[andrewrk]

See #539. Currently we only look for msvc 2015 but we should look for 2017 as well. Also there are command line args for setting the msvc path at runtime. Look for msvc in the --help menu.

[andrewrk]

Example now gives:

/home/andy/dev/zig/build/test.zig:1:11: error: C import failed
const c = @cImport(@cInclude("stdio.h"));
          ^
/home/andy/dev/zig/build/test.zig:1:11: note: libc headers not available; compilation does not link against libc
const c = @cImport(@cInclude("stdio.h"));
          ^
/run/user/1000/T1mB37.h:1:10: note: 'stdio.h' file not found
#include <stdio.h>
         ^

[Lucifer-02]

how to fix this?