Comptime type inference

[Sze]

@affine-root-system

If the former is not called at compile time then I can’t image the latter would be - how would the compiler know to treat them differently?

Hmm, yes I think you are right with that.

@compileError triggers when it is reached during semantic analysis, but comptime / compile time execution of functions also happens during semantic analysis.

From:

How Zig incremental compilation is implemented internally?

Nice question! I can give an overview here – I’m also intending to do a proper write-up of the system at some point into a docs file in the Zig repo, although that’ll probably assume a bit more technical background (since it’ll be targeted towards existing compiler devs). First, we need to understand the compiler pipeline. After parsing (which is boring), there are three important stages: AstGen Sema CodeGen AstGen consumes a parsed AST and generates an instruction-based intermediate represe…

After we have generated all of our ZIR, then we have Sema. This is the heart of the compiler – it’s the stage that performs semantic analysis, which includes type checking, comptime code execution, most error messages, etc. Sema interprets the ZIR which AstGen emitted and turns it into AIR (Analyzed Intermediate Representation), a much more simple and low-level IR which is sent to the code generator. CodeGen is actually interleaved with Sema: after a function is semantically analyzed, it’s immediately sent to the code generator.

For the rest read the linked post. So I think I would rephrase:

@Sze

but one reason why I think it has to run f(x) is …

I think it runs whatever comptime parts there are within the function (if there are any).

Not completely sure, that is just my best guess at the moment.
I think for a better answer I would have to dig into the implementation myself. (Which I want to do eventually, but haven’t done yet)