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rockssalt05 opened this issue May 1, 2025 · 1 comment · May be fixed by #23882
Open

Sentinel value isn't set when array is initialized #23739

rockssalt05 opened this issue May 1, 2025 · 1 comment · May be fixed by #23882
Labels
bug Observed behavior contradicts documented or intended behavior
Milestone
0.15.0

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@rockssalt05
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rockssalt05 commented May 1, 2025 •
edited
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Zig Version

0.15.0-dev.386+2e35fdd03

Steps to Reproduce and Observed Behavior

Run this program with zig test

// this doesn't set the sentinel
fn func1(yes: bool) [2:'!']u8 {
    return .{
        'h',
        if (yes) 'i' else 'a'
    };
}

// this does
fn func2(yes: bool) [2:'!']u8 {
    return @as([2:'!']u8, .{
        'h',
        if (yes) 'i' else 'a'
    });
}

test {
    const arr = func1(true);
    const slice = arr[0.. :'!'];
    _ = slice;
}

Whether the @as() is there or not shouldn't matter if I'm not mistaken
It works as expected if you remove the if statement

Using func1, it crashes with a garbage sentinel value

thread 5079 panic: sentinel mismatch: expected 33, found 252
./test.zig:21:22: 0x1048abf in test_0 (test)
    const slice = arr[0.. :'!'];
                     ^
/usr/local/zig-linux-x86_64-0.15.0-dev.386+2e35fdd03/lib/compiler/test_runner.zig:214:25: 0x10efc59 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/usr/local/zig-linux-x86_64-0.15.0-dev.386+2e35fdd03/lib/compiler/test_runner.zig:62:28: 0x10e7ebd in main (test)
        return mainTerminal();
                           ^
/usr/local/zig-linux-x86_64-0.15.0-dev.386+2e35fdd03/lib/std/start.zig:662:22: 0x10e7360 in posixCallMainAndExit (test)
            root.main();
                     ^
/usr/local/zig-linux-x86_64-0.15.0-dev.386+2e35fdd03/lib/std/start.zig:282:5: 0x10e6f2d in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
./test --seed=0xa2a79302

Expected Behavior

func1 and func2 behave the same
@rockssalt05 rockssalt05 added the bug Observed behavior contradicts documented or intended behavior label May 1, 2025
@rockssalt05
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This is similar to #4372, but using .{} in the initializer instead
So you can reduce the test program even further to this

test {
    var h: u8 = 'h';
    _ = &h;
    const arr: [2:'!']u8 = .{h, 'i'};
    const slice = arr[0.. :'!'];
    _ = slice;
}

@rockssalt05 rockssalt05 changed the title Sentinel value isn't set when returning sentinel terminated array from a function Sentinel value isn't set when array is initialized May 3, 2025
@rockssalt05 rockssalt05 linked a pull request May 14, 2025 that will close this issue
Open
@mlugg mlugg added this to the 0.14.1 milestone May 15, 2025
@alexrp alexrp modified the milestones: 0.14.1, 0.15.0 May 18, 2025
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bug Observed behavior contradicts documented or intended behavior
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Fix sentinel value not being set in runtime array init rockssalt05/zig
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@alexrp @mlugg @rockssalt05