Compilation error caused by weird `test::@error` and `mem::equal` interferrence.

[alexveden]

Minimal code (you may need to add some imports, because I carved this snippet from another code):

module test;
import std::io;


struct MyFoo {
    uint idx;
}

struct MyFooIter {
    MyFoo* parent;
    uint idx;
}

macro MyFooIter MyFoo.iter(&self) {
    return (MyFooIter){.parent = self};
}

macro MyFoo*! MyFooIter.next(&self) {
    MyFoo foo = {.idx = 999};

    // expected to always fail
    if (!mem::equals(&foo, self.parent, MyFoo.sizeof)) {
        return IoError.GENERAL_ERROR?;
    }

    return self.parent;
}

module test @test;
fn void test_myfoo()
{
    MyFoo foo;
    MyFooIter iter = foo.iter();

    // This will compile and blow up with GENERAL_ERROR (expected)
    // iter.next()!!;
    
    // This doesn't compile with weird error
    test::@error(iter.next(),  IoError.GENERAL_ERROR);
}

Error:

 416: macro bool equals(a, b, isz len = -1, usz $align = 0)
 417: {
 418:   $if !$align:
 419:           $align = $typeof(a[0]).alignof;
                ^^^^^^
(/home/ubertrader/code/c3c/lib/std/core/mem.c3:419:3) Error: Compile time variables may only be modified in the scope they are defined in.

 70: macro MyFoo*! MyFooIter.next(&self) {
 71:     MyFoo foo = {.idx = 999};
 72:
 73:     if (!mem::equals(&foo, self.parent, MyFoo.sizeof)) {
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(/home/ubertrader/code/c3tools/test/c3tools/lsp/test_symhash.c3:73:10) Note: Inlined from here.

 88: *>
 89: macro @error(#funcresult, anyfault error_expected)
 90: {
 91:    if (catch err = #funcresult) {
                        ^^^^^^^^^^^
(/home/ubertrader/code/c3c/lib/std/core/test.c3:91:18) Note: Inlined from here.

 442:                   $Type = uint;
 443:           $case 8:
 444:           $default:
 445:                   $Type = ulong;
                        ^^^^^
(/home/ubertrader/code/c3c/lib/std/core/mem.c3:445:4) Error: Compile time variables may only be modified in the scope they are defined in.

 70: macro MyFoo*! MyFooIter.next(&self) {
 71:     MyFoo foo = {.idx = 999};
 72:
 73:     if (!mem::equals(&foo, self.parent, MyFoo.sizeof)) {
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(/home/ubertrader/code/c3tools/test/c3tools/lsp/test_symhash.c3:73:10) Note: Inlined from here.

 88: *>
 89: macro @error(#funcresult, anyfault error_expected)
 90: {
 91:    if (catch err = #funcresult) {
                        ^^^^^^^^^^^
(/home/ubertrader/code/c3c/lib/std/core/test.c3:91:18) Note: Inlined from here.

 444:           $default:
 445:                   $Type = ulong;
 446:   $endswitch
 447:   var $step = $Type.sizeof;
                    ^^^^^
(/home/ubertrader/code/c3c/lib/std/core/mem.c3:447:14) Error: You need to assign a type to '$Type' before using it.

C3 Compiler Version:       0.6.8 (Pre-release, Feb 20 2025 11:29:04)
Installed directory:       /home/ubertrader/code/c3c/build/
Git Hash:                  e97ff1ce21bddc6dc4d406b42c983f35d16982fc
Backends:                  LLVM
LLVM version:              18.1.8
LLVM default target:       x86_64-pc-linux-gnu

[alexveden]

I also found that @catch may produce the similar error

assert(@catch(iter.next()) ==  IoError.GENERAL_ERROR);

[lerno]

This is a problem with detecting that the compile time variable isn't actually modified inside of the other macro context. I need to think a little about this.

[BWindey]

Chiming in to say I also encountered this, and managed to create a pretty minimal example:

macro int[] @add_sum(int[] $array) {
	int $sum = 0;
	$for var $i = 0; $i < 2; $i++ :
		$sum = $sum + $array[$i];
	$endfor
	return { $array[0] + $sum, $array[1] };
}

macro @test_comptime(#e1, #e2) {
	var $Type = $typeof(#e1);
	assert(
		#e1 == #e2,
		"Assertion '" +++ $stringify(#e1) +++ " == " +++ $stringify(#e2)
		+++ "' failed, got '%s', expected '%s'.", #e1, ($Type) #e2
	);
}

fn void main() {
	@test_comptime(@add_sum({ 1, 2 }), (int[]) { 1, 3 });
}

With the following error twice (I guess because for-loop runs twice):

 1: macro int[] @add_sum(int[] $array) {
 2:     int $sum = 0;
 3:     $for var $i = 0; $i < 2; $i++ :
 4:             $sum = $sum + $array[$i];
                ^^^^
(.../hello.c3:4:3) Error: Compile time variables may only be modified in the scope they are defined in.

11:     assert(
12:             #e1 == #e2,
13:             "Assertion '" +++ $stringify(#e1) +++ " == " +++ $stringify(#e2)
14:             +++ "' failed, got '%s', expected '%s'.", #e1, ($Type) #e2
                                                          ^^^
(.../hello.c3:14:45) Note: Inlined from here.

[BWindey]

Note that a work-around in my example would be to assign #e1 and #e2 to a $ variable inside the @test_comptime macro, and use that $ variable in the assert.

[lerno]

I'll just remove the detection for now.

[BWindey]

In what way did you fix it?
I just grabbed the latest commit and compiled the compiler, still has the same error.

My workaround by assigning the #e1 to $e1 does not work anymore:

macro int[] @add_sum(int[] $array) {
	int $sum = 0;
	$for var $i = 0; $i < 2; $i++ :
		$sum = $sum + $array[$i];
	$endfor
	return { $array[0] + $sum, $array[1] };
}

macro @test_comptime(#e1, #e2) {
	var $e1 = #e1;
	var $e2 = #e2;
	var $Type = $typeof($e1);
	assert(
		$e1 == $e2,
		"Assertion '" +++ $stringify($e1) +++ " == " +++ $stringify($e2)
		+++ "' failed, got '%s', expected '%s'.", $e1, ($Type) $e2
	);
}

fn void main() {
	@test_comptime(@add_sum({ 1, 2 }), (int[]) { 1, 3 });
}

Gives this:

 1: macro int[] @add_sum(int[] $array) {
 2:     int $sum = 0;
 3:     $for var $i = 0; $i < 2; $i++ :
 4:             $sum = $sum + $array[$i];
                ^^^^
Error: Compile time variables may only be modified in the scope they are defined in.

 7: }
 8: 
 9: macro @test_comptime(#e1, #e2) {
10:     var $e1 = #e1;
                  ^^^
Note: Inlined from here.