Poor compilation warning for error propogation in loop

[joshmeranda]

Describe the bug

When using an error propagation in a for loop, I get an error message:

>>> v -cg .
/tmp/v_1001/vsweeper.161389303863868986.tmp.c:12580: error: ')' expected (got "_t1")

This is very unhelpful in debugging and finding the error, and confusing to newcomers to vlang like me. Ideally, we'd get something similar to when trying to use the alternative or for options.

src/main.v:9:24: error: options are not allowed in `for statement increment` (yet)
    7 | fn main() {
    8 |     mut pos := 0
    9 |     for ; pos > 10; pos = foo() or { 6 } {
      |                           ~~~~~
   10 |         println(pos)
   11 |     }

Reproduction Steps

Run each each of the loops below with v -cg .

module main

fn foo() !int {
	return 5
}

fn main() {
	mut pos := 0

	// /tmp/v_1001/vsweeper.161389303863868986.tmp.c:12580: error: ')' expected (got "_t1")
	for ; pos > 10; pos = foo()! {
		println(pos)
	}

	// /tmp/v_1001/vsweeper.7081838145059576425.tmp.c:12579: error: identifier expected
	for pos = foo()!; pos > 10; {
		println(pos)
	}

	// no error
	// for ; pos < foo()!; {
	// 	println(pos)
	// }
}

Expected Behavior

Output the same or similar options are not allowed in 'for statement increment' (yet) as when using error propagation in for loop.

Current Behavior

Compilation fails with warnings:

/tmp/v_1001/vsweeper.161389303863868986.tmp.c:12580: error: ')' expected (got "_t1")

and

/tmp/v_1001/vsweeper.7081838145059576425.tmp.c:12579: error: identifier expected

Possible Solution

Might be possible to handle this the same way v checks for the for i :=0; i < 10; i = foo! { or 5 }

Additional Information/Context

No response

V version

V 0.4.2 65d7126

Environment details (OS name and version, etc.)

V full version: V 0.4.2 7e2d737.65d7126
OS: linux, Ubuntu 22.04.3 LTS
Processor: 16 cpus, 64bit, little endian, 13th Gen Intel(R) Core(TM) i7-1360P

getwd: /home/wrinkle/workspaces/joshmeranda/vsweeper
vexe: /home/wrinkle/workspaces/vlang/v/v
vexe mtime: 2023-10-23 01:52:31

vroot: OK, value: /home/wrinkle/workspaces/vlang/v
VMODULES: OK, value: /home/wrinkle/.vmodules
VTMP: OK, value: /tmp/v_1001

Git version: git version 2.34.1
Git vroot status: weekly.2023.42-28-g65d71269
.git/config present: true

CC version: cc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
thirdparty/tcc status: thirdparty-linux-amd64 12f392c3

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[HimanshuMahto]

hey, I'm new to this and would like to contribute to this. Can you please assign me this issue.

[medvednikov]

@HimanshuMahto sure, you can just submit a PR.

Thanks.