xml encoding fails with C compiler error

[louis77]

Describe the bug

Converting a xml.XMLNode to a string fails with a C compiler error, when the node's children reference a string variable, like shown in the example. However, it works when the string is cloned.

Reproduction Steps

module main

import encoding.xml

fn main() {
	str := "hello"

	node := xml.XMLNode{
		name: "soapenv:Envelope",
		attributes: {
			"xmlns:soapenv": 'http://schemas.xmlsoap.org/soap/envelope/',
			"xmlns:io": 'http://example.org/'
		},
		children: [
			xml.XMLNode{
				name: "soapenv:Header"
			},
			xml.XMLNode{
				name: "soapenv:Body",
				children: [str]
			}
		]
	}

	dump(node.pretty_str("  ", 1, xml.default_entities_reverse))
}

The problem disappears, when the string is cloned instead:

	xml.XMLNode{
		name: "soapenv:Body",
		children: [str.clone()]
	}

Expected Behavior

The encoding should work without a call to string.clone(). This should be handled inside the encoding.xml library.

Current Behavior

The V compiler fails while building with the following message:

% v run xml.v
================== C compilation error (from cc): ==============
cc: /tmp/v_501/xml.01JH9D67CFF9PPBTYQ1R9NGKGJ.tmp.c:8809:878: error: initializing 'encoding__xml__XMLCData *' (aka 'struct encoding__xml__XMLCData *') with an expression of incompatible type 'string' (aka 'struct string')
cc:  8809 |         ,.children = new_array_from_c_array(2, 2, sizeof(encoding__xml__XMLNodeContents), _MOV((encoding__xml__XMLNodeContents[2]){encoding__xml__XMLNode_to_sumtype_encoding__xml__XMLNodeContents(ADDR(encoding__xml__XMLNode, (((encoding__xml__XMLNode){.name = _SLIT("soapenv:Header"),.attributes = new_map(sizeof(string), sizeof(string), &map_hash_string, &map_eq_string, &map_clone_string, &map_free_string),.children = __new_array(0, 0, sizeof(encoding__xml__XMLNodeContents)),})))), encoding__xml__XMLNode_to_sumtype_encoding__xml__XMLNodeContents(ADDR(encoding__xml__XMLNode, (((encoding__xml__XMLNode){.name = _SLIT("soapenv:Body"),.attributes = new_map(sizeof(string), sizeof(string), &map_hash_string, &map_eq_string, &map_clone_string, &map_free_string),.children = new_array_from_c_array(1, 1, sizeof(encoding__xml__XMLNodeContents), _MOV((encoding__xml__XMLNodeContents[1]){string_clone(str)})),}))))})),});
cc:       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     ^~~~~~~~~~~~~~~~~
cc: /tmp/v_501/xml.01JH9D67CFF9PPBTYQ1R9NGKGJ.tmp.c:250:38: note: expanded from macro 'ADDR'
cc:   250 | #define ADDR(type, expr) (&((type[]){expr}[0]))
cc:       |                                      ^~~~
cc: 1 error generated.
================================================================
(You can pass `-cg`, or `-show-c-output` as well, to print all the C error messages).
builder error: 
==================
C error found. It should never happen, when compiling pure V code.
This is a V compiler bug, please report it using `v bug file.v`,
or goto https://github.com/vlang/v/issues/new/choose .
You can also use #help on Discord: https://discord.gg/vlang .

Possible Solution

The pretty_str function should handle necessary allocations/cloning of strings.

Additional Information/Context

No response

V version

V 0.4.9 63f5f4a

Environment details (OS name and version, etc.)

|V full version      |V 0.4.9 7af8faf.63f5f4a
|:-------------------|:-------------------
|OS                  |macos, macOS, 15.2, 24C101
|Processor           |8 cpus, 64bit, little endian, Apple M2
|Memory              |0.33GB/16GB
|                    |
|V executable        |/Users/user/Git/nv/v
|V last modified time|2025-01-10 15:29:47
|                    |
|V home dir          |OK, value: /Users/user/Git/nv
|VMODULES            |OK, value: /Users/user/.vmodules
|VTMP                |OK, value: /tmp/v_501
|Current working dir |OK, value: /Users/user/Git/vproj/cmd
|                    |
|Git version         |git version 2.39.5 (Apple Git-154)
|V git status        |weekly.2025.1-29-g63f5f4a6-dirty
|.git/config present |true
|                    |
|cc version          |Apple clang version 16.0.0 (clang-1600.0.26.4)
|gcc version         |Apple clang version 16.0.0 (clang-1600.0.26.4)
|clang version       |Homebrew clang version 18.1.8
|tcc version         |tcc version 0.9.28rc 2024-02-05 HEAD@105d70f7 (AArch64 Darwin)
|tcc git status      |thirdparty-macos-arm64 713692d4
|emcc version        |N/A
|glibc version       |N/A

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[felipensp]

A workound would be:
children: [xml.XMLNodeContents(str)]

[felipensp]

Short test case:

type SumFoo = int | string

struct Foo {
	bar []SumFoo
}

struct Bar {
	foo []Foo
}

fn main() {
	str := 'foobar'
	_ := Bar{
		foo: [Foo{
			bar: [str],
		}]
	}	
}