pragma(explicit_gc)

[Timon Gehr]

On 5/2/24 03:45, Timon Gehr wrote:
> Often, GC is nice but collections should be avoided in an inner loop. 
> `@nogc` is too restrictive because may be fine to e.g., allocate an 
> `Exception` before throwing it, and programmers are aware that such 
> allocations are happening.
> 
> A somewhat more insidious case is implicit allocation, because even when 
> programs look like they do need to allocate, they may in fact allocate 
> due to the compiler's escape analysis being too weak.
> 
> For example, there is no reason for the following program to allocate 
> with the GC, but it does implicitly allocate a closure:
> 
> ```d
> void main(){ // errors with @nogc
>      auto y=2;
>      assert(iota(10).filter!((x)=>x%y!=0).sum==25);
> }
> ```
> 
> In case the GC is disabled, such imprecise escape analysis in an inner 
> loop may result in a memory leak.
> 
> Proposal: Add `pragma(explicit_gc)`. Functions marked with this pragma 
> will non-transitively error out on implicit GC allocations. This is a 
> useful tool to check expectations about escape analysis precision.

Merged into OpenD: https://github.com/opendlang/opend/pull/69

Can be cherry-picked from there.