Compiler crash when @memsetting member array

[Srekel]

Zig Version

0.11.0-dev.3031+f40539e5d

Steps to Reproduce and Observed Behavior

This is on Windows 10.

zig init

main.zig:

pub const IdLocal = struct {
    str: [191]u8 = .{0} ** 191,

    pub fn clear(self: *IdLocal) void {
        // @memset(self.str[0..], 0); <--- this is correct and works
        @memset(self.str, 0); // <--- this yields "exit code 1"
    }
};

pub fn main() !void {
    var lol: IdLocal = undefined;
    lol.clear();
}

zig build:

PS E:\Projects\zigtesting> zig build
zig build-exe zigtesting Debug native: error: the following command exited with error code 3:
E:\Programs\zig\zig.exe build-exe E:\Projects\zigtesting\src\main.zig --cache-dir E:\Projects\zigtesting\zig-cache --global-cache-dir C:\Users\Srekel\AppData\Local\zig --name zigtesting --listen=-
Build Summary: 0/3 steps succeeded; 1 failed (disable with -fno-summary)
install transitive failure
+- install zigtesting transitive failure
+- zig build-exe zigtesting Debug native failure
error: the following build command failed with exit code 1:
E:\Projects\zigtesting\zig-cache\o\d234a84f47ea5d41edd005b7e6d7c6fb\build.exe E:\Programs\zig\zig.exe E:\Projects\zigtesting E:\Projects\zigtesting\zig-cache C:\Users\Srekel\AppData\Local\zig
PS E:\Projects\zigtesting>

Expected Behavior

PS E:\Projects\zigtesting> zig build
PS E:\Projects\zigtesting>

[hqhs]

The platform doesn't matter. I reproduced this on osx with a bit smaller example:

pub fn main() !void {
    var s = [_]u8{0} ** 191;
    // @memset(&s, 0); // works
    @memset(s, 0); // doesn't
}

@memset destination correctness check happens in Sema.zig zirMemset.

My guess the line try checkIndexable(sema, block, dest_src, dest_ptr_ty);
is not enough. It probably was intended for for loops checking only, e.g., the following code crashes the compiler too:

pub fn main() !void {
    const tuple_s = .{ @as(usize, 2), @as(usize, 4) };
    @memset(&tuple_s, @as(usize, 5));
}

Since tuples are indexable.

From the docs:

dest must be a mutable slice or a mutable pointer to an array. It may have any alignment, and it may have any element type.

In the cases above, dest is indexable, but it's not a pointer to an array.

If the doc is correct and the compiler isn't, then the fix is to restrict type checking of dest to .Pointers only.

[hqhs]

I created a small PR with the possible fix: #15638

[hqhs]

The alternative fix would be to properly implement memset for all remaining indexable containers like proposed here #15479

[jacobly0]

Related #15633 (similar issue, but with @memcpy)