Add support for version as expression

[bangbangsheshotmedown]

D is healing

enum value = version(linux) ? 42 : 0;

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[bangbangsheshotmedown]

2025-01-27T10:13:52.1539227Z src\dmd\parse.d(8629): Error: no property `versionids` for `this.mod` of type `dmd.astbase.ASTBase.Module`
2025-01-27T10:13:52.1570805Z 
2025-01-27T10:13:52.1572527Z                 if (mod.versionids && findCondition(*mod.versionids, condition.ident))
2025-01-27T10:13:52.1575043Z 
2025-01-27T10:13:52.1605930Z                        ^

i don't understand, the code compiles on my machine

And i also realize that this will not work since it's not done parsing, perhaps someone can help

[dkorpel]

The parser is standalone, not dependent on dmd's semantic code. It is templated and can be instantiated both with DMD's AST (with extra semantic info), or 'astbase', a parser only version of the AST. Your code tries to access semantic info versionids which works when compiling dmd, but not in the test for using DMD as a library with astbase.

The duplicated astbase.d module is rather ugly and work is being done to remove it by refactoring dmd's ast to be separate from semantic routines (https://github.com/orgs/dlang/projects/41), but even so, the implementation of this feature should probably not try to resolve the version during parsing.

The proper implementation solution is to create a new Expression node similar to the VersionCondition node and resolve it during semantic. However, I would not spend much effort on this feature as it's likely going to be rejected. The addition of version algebra has been discussed to death without being fruitful.

[bangbangsheshotmedown]

Thanks for the detailled explanation, i'll rework this PR

However, I would not spend much effort on this feature as it's likely going to be rejected. The addition of version algebra has been discussed to death without being fruitful.

Well, i disagree with that

Nobody will convince me that this is good:

version(linux)
{
    enum value = 42;
}
else
{
    enum value = 0;
}

[Geod24]

Has this been approved ? @WalterBright has been consistently against it.

[12345swordy]

What problem are you trying to solve?

[bangbangsheshotmedown]

What problem are you trying to solve?

The example in the change log entry is self explanatory, makes simple cases easier to process

8 lines of code vs just 1

Right now i solve it with:

struct Version
{
    static bool opDispatch(string identifier)()
    {
        mixin("
            version(", identifier, ")
                return true;
            else
                return false;
        ");
    }
}

This however feels like over-engineering for something that should be simple, and i am not a fan of having to import a module, i never remember wich file has this code and let's be honest, an import for this is cringe

[bangbangsheshotmedown]

That's the only thing i miss from C, having to include my utility file only once

Perhaps D could have something like C#'s global using, so i could have my utility module always available without having to import it everywhere

This would solve my issue

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-directive#the-global-modifier

[Lars-Kristiansen]

That does not work. The change is sold as an expression but if so you have to support

void v(T)(T t);
void main()
{
    v!int(version(linux) ? 42 : 0);
}

such a feature requires much more work.