cgen, generics: nested generic str() (a generic field whose type param is itself generic) is not emitted #12

Description

When a generic struct's auto-generated str() method needs to stringify a nested generic type (a generic struct field whose type parameter is itself a generic instantiation), the str() method for that nested type is referenced but never generated, so the C compiler fails with an undeclared-function error.

V version: V 0.5.1, current master (ddb021b98) OS/Backend: reproduced on macOS arm64; originally reported on macOS/cc.

Reproducer

import datatypes

struct MyNode[T] {
    val T
}

struct MyContainer[T] {
    lst datatypes.LinkedList[MyNode[T]]
}

fn main() {
    c := MyContainer[string]{}
    println(c)
}

Compile with:

v file.v

Current behavior

error: call to undeclared function 'datatypes__LinkedList_T_main__MyNode_T_string_str_T_main__MyNode_T_string'
  string _t1 = datatypes__LinkedList_T_main__MyNode_T_string_str_T_main__MyNode_T_string(it.lst);

The auto-str for MyContainer[string] calls the str() of its LinkedList[MyNode[string]] field, but that nested generic str() instantiation is never emitted.

Expected behavior

The str() method for the nested generic type (LinkedList[MyNode[string]]) should be generated, so printing the container compiles and works.

Notes

• Reported via the bugs.vlang.io crash reporter (3 reports). Original file name: generic_struct_parameter_err.

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