selective imports complain about "unused" module

[Elsie19]

Describe the bug

When I create a local module and selectively import something from it, v will complain about the module being imported but unused even though I selectively imported something from it. While this is technically true, it doesn't make much sense from a developer perspective, as using any publicly available code from the module should count as using the module.

Reproduction Steps

src/lib.v:

module qbe

// qbe is a library to generate QBE IR using Vlang data structures.

// Type sets the length of a type.
pub enum Type {
	// 32-bit integer
	word
	// 64-bit integer
	long
	// 32-bit float
	single
	// 64-bit float
	double
	wordbyte
	longbyte
	singlebyte
	doublebyte
	wordhalf
	longhalf
	singlehalf
	doublehalf
}

// String representation of enum values.
pub fn (t Type) str() string {
	return match t {
		.word { 'w' }
		.long { 'l' }
		.single { 's' }
		.double { 'd' }
		.wordbyte { 'wb' }
		.longbyte { 'lb' }
		.singlebyte { 'sb' }
		.doublebyte { 'db' }
		.wordhalf { 'wh' }
		.longhalf { 'lh' }
		.singlehalf { 'sh' }
		.doublehalf { 'dh' }
	}
}

src/main.v:

import qbe { Type }

fn main() {
	println(Type.word.str())
}

v.mod:

Module {
	name: 'qbe'
	description: 'Clone of https://github.com/garritfra/qbe-rs in V'
	version: '0.0.1'
	license: 'MIT'
	dependencies: []
}

Expected Behavior

I should not get a warning about the module being imported but unused when I use any code inside that module, as using that code should count as using the module.

Current Behavior

When doing v run ., I get the warning:

src/main.v:1:8: warning: module 'qbe' is imported but never used
    1 | import qbe { Type }
      |        ~~~
    2 |
    3 | fn main() {
w

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.8 b801083

Environment details (OS name and version, etc.)

V full version: V 0.4.8 1931811.b801083
OS: linux, Ubuntu 24.10
Processor: 6 cpus, 64bit, little endian, Intel(R) Core(TM) i5-9400 CPU @ 2.90GHz

getwd: /home/henry/Projects/v/qbe
vexe: /home/henry/Projects/v/vcompiler/v
vexe mtime: 2024-11-25 18:10:30

vroot: OK, value: /home/henry/Projects/v/vcompiler
VMODULES: OK, value: /home/henry/.vmodules
VTMP: OK, value: /tmp/v_1000

Git version: git version 2.45.2
Git vroot status: b801083 (4 commit(s) behind V master)
.git/config present: true

CC version: cc (Ubuntu 14.2.0-4ubuntu2) 14.2.0
emcc version: N/A
thirdparty/tcc status: thirdparty-linux-amd64 0134e9b9

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[Wajinn]

Imported module name can be aliased using the as keyword
You cannot alias an imported function or type. However, you can redeclare a type.

Thus the below would work, for the case presented.

import qbe as kind // {Type}

type Type = kind.Type

fn main() {
	println(kind.Type.word.str())
	println(Type.word.str())
}

or

import qbe 

fn main() {
	println(qbe.Type.word.str())
}

However, I do think team V may want to be careful about pushing modules into the same category as unused variables. As I have come across older modules (that were listed on VPM) that worked on a previous version of V, but then gave the "unused module" error as described above, on newer V versions. It should be clear that a programmer may not use everything from an imported module.

[JalonSolov]

You don't have to use everything from an imported module, but you do need to use something.

In this case, it's just a bug that it didn't count it as used.

[Wajinn]

What you are saying should be true, but If I remember correctly, this could pertain to a module with multiple files and referencing other modules as well. I would have to go back and investigate again, as had worked around the issue. But mentioning it, as seeing "unused module" jarred my memory.

[spytheman]

You can do import mod as _, if you want to import it, just for the side effects (due to potential const initialisations that call functions, or the module's init function), without using any symbols.

[spytheman]

The issue is indeed just a bug - because the symbol Type is used in the user code later.
The compiler should note that, and not trigger a warning at all in this case.

[JalonSolov]

Fixed by #23626