Compiler error using array concatenation with inferred types

[jeffkdev]

Minimal test. Printed error: assertion failed. This is a bug in the Zig compiler.

pub fn main() void {
    const works: [4]f32 = .{1,2,3,4};
    const compiler_bug: [4]f32 = .{1,2} ++ .{3,4};
}

I am not 100% sure if the second line is supposed to be compilable, but minimally needs some sort of compiler error.

But assuming the compiler_bug line is correct, then below I added some slightly more complex test cases that would make sense if they worked as well:

const StructWithDefault = struct {
    value: f32 = 42,
};
const SomeStruct = struct {
    array: [4]StructWithDefault,
};

pub fn main() void {
    // Ok #1: Array element type inferred
    const value0 = SomeStruct{ .array = [_]StructWithDefault{.{}} ++ [_]StructWithDefault{undefined} ** 3 };
    // Ok #2: Array type inferred from defined elements
    const value1 = SomeStruct{ .array = .{ StructWithDefault{}, StructWithDefault{}, StructWithDefault{}, StructWithDefault{} } };
    // Ok #3: Array type and element type inferred
    const value2 = SomeStruct{ .array = .{ .{}, .{}, .{}, .{} } };
    // error #1: error: expected array, found 'struct:14:4'2 (Define element type, remove array type definition)
    const value3 = SomeStruct{ .array = .{StructWithDefault{}} ++ [_]StructWithDefault{undefined} ** 3 };
    // error #2: error: expected array, found 'struct:16:42' (Remove element type and array type in first arg)
    const value4 = SomeStruct{ .array = .{.{}} ++ [_]StructWithDefault{undefined} ** 3 };
    // error #3: error: expected array, found 'struct:18:52' (Remove element type and array type in both args)
    const value5 = SomeStruct{ .array = .{.{}} ++ .{undefined} ** 3 };
    // error #4: assertion failed. This is a bug in the Zig compiler.
    const value6 = SomeStruct{ .array = .{ .{}, .{}, } ++ .{.{}, .{} }} ;
}

My actual use case involves serializing an inline array (fixed max length, variable number of elements)
to zig code where I only want to define the elements that are actually populated and leave the rest undefined. Explicitly defining the array type like in Ok #1 let me workaround this for now.

0.5.0+b55bc5e

[LemonBoy]

Duplicate of #3979!

[jeffkdev]

Thanks. Closing this one. Will add the more complex test case to the original.

[jeffkdev]

This was initially closed as a duplicate, but #3979 didn't fix all the cases above this when it was closed. I didn't find another open issue that covered these.

Shorter example with just the lines that aren't working:

const StructWithDefault = struct {
    value: f32 = 42,
};
const SomeStruct = struct {
    array: [4]StructWithDefault,
};

pub fn main() void {
    // error #1
    const value3 = SomeStruct{ .array = .{StructWithDefault{}} ++ [_]StructWithDefault{undefined} ** 3 };
    // error #2
    const value4 = SomeStruct{ .array = .{.{}} ++ [_]StructWithDefault{undefined} ** 3 };
}

error 1

.\test.zig:10:42: error: expected array, found 'struct:10:42'
    const value3 = SomeStruct{ .array = .{StructWithDefault{}} ++ [_]StructWithDefault{undefined} ** 3 };
                                         ^
.\test.zig:10:64: note: referenced here
    const value3 = SomeStruct{ .array = .{StructWithDefault{}} ++ [_]StructWithDefault{undefined} ** 3 };

error 2

.\test.zig:12:42: error: expected array, found 'struct:12:42'
    const value4 = SomeStruct{ .array = .{.{}} ++ [_]StructWithDefault{undefined} ** 3 };
                                         ^
.\test.zig:12:48: note: referenced here
    const value4 = SomeStruct{ .array = .{.{}} ++ [_]StructWithDefault{undefined} ** 3 };
                                               ^

Both errors can be worked around by adding the array type first: .array = [_]StructWithDefault.

Zig version: 0.9.0-dev.70+a3f7a48d9

[nektro]

not sure if this is in scope for type inference