ast: proposed fix for list of generic bug

[kimshrier]

I ran in to another code generation bug while I was playing around with generics.

The following code shows the problem:

module main

struct Container[T] {}

pub fn (c Container[T]) get() !T {
	return T{}
}

fn make_list[T]() Container[[]T] {
	return Container[[]T]{}
}

fn test_make_list() {
	_ := make_list[int]()
	assert true
}

Prior to making the change, I would see the following error:

$ v test /private/tmp/generic_method_slice_test.v
---- Testing... ------------------------------------------------------------------------------------
/private/tmp/generic_method_slice_test.v:6:9: error: cannot use `[][][]T` as type `![][]T` in return argument
    4 | 
    5 | pub fn (c Container[T]) get() !T {
    6 |     return T{}
      |            ~~~
    7 | }
    8 |
 FAIL     0.000 ms /private/tmp/generic_method_slice_test.v
>> compilation failed:
/private/tmp/generic_method_slice_test.v:6:9: error: cannot use `[][][]T` as type `![][]T` in return argument
    4 | 
    5 | pub fn (c Container[T]) get() !T {
    6 |     return T{}
      |            ~~~
    7 | }
    8 |

----------------------------------------------------------------------------------------------------
To reproduce just failure 1 run:    '/Users/kim/Projects/v/from_github/v/v'  '/private/tmp/generic_method_slice_test.v'
Summary for all V _test.v files: 1 failed, 1 total. Elapsed time: 846 ms, on 1 job. Comptime: 792 ms. Runtime: 0 ms.

After applying the change, the error goes away:

$ v test /private/tmp/generic_method_slice_test.v
---- Testing... ------------------------------------------------------------------------------------
 OK     406.864 ms /private/tmp/generic_method_slice_test.v
----------------------------------------------------------------------------------------------------
Summary for all V _test.v files: 1 passed, 1 total. Elapsed time: 713 ms, on 1 job. Comptime: 305 ms. Runtime: 406 ms.

$ v doctor
|V full version      |V 0.5.1 ed5fc1638abe439f5b4d5d31e0c91a81af065b94
|:-------------------|:-------------------
|OS                  |macos, macOS, 26.4.1, 25E253
|Processor           |10 cpus, 64bit, little endian, Apple M1 Max
|Memory              |1.3GB/64GB
|                    |
|V executable        |/Users/kim/Projects/v/from_github/v/v
|V last modified time|2026-05-10 21:34:03
|                    |
|V home dir          |OK, value: /Users/kim/Projects/v/from_github/v
|VMODULES            |OK, value: /Users/kim/.vmodules
|VTMP                |OK, value: /tmp/v_1002
|Current working dir |OK, value: /Users/kim/Projects/Github/v
|                    |
|env LDFLAGS         |"-L/opt/homebrew/opt/postgresql@15/lib"
|Git version         |git version 2.50.1 (Apple Git-155)
|V git status        |0.5.1-1536-ged5fc163-dirty
|.git/config present |true
|                    |
|cc version          |Apple clang version 21.0.0 (clang-2100.0.123.102)
|gcc version         |Apple clang version 21.0.0 (clang-2100.0.123.102)
|clang version       |Apple clang version 21.0.0 (clang-2100.0.123.102)
|tcc version         |tcc version 0.9.28rc 2026-01-10 HEAD@5ec0e6f8 (AArch64 Darwin)
|tcc git status      |thirdparty-macos-arm64 f995efa3
|emcc version        |N/A
|glibc version       |N/A

[medvednikov]

thanks, but needs a test