* Indices of referenced captures
* Line and column of `@src()`
The second point aligns with a reversal of the "incremental compilation"
section of https://github.com/ziglang/zig/issues/2029#issuecomment-645793168.
This reversal was already done as #17688 (46a6d50), with the idea to
push incremental compilation down the line. My proposal is to keep it as
comptime-known, and simply re-analyze uses of `@src()` whenever their
line/column change.
I think this decision is reasonable for a few reasons:
* The Zig compiler is quite fast. Occasionally re-analyzing a few
functions containing `@src()` calls is perfectly acceptable and won't
noticably impact update times.
* The system described by Andrew in #2029 is currently vaporware.
* The system described by Andrew in #2029 is non-trivial to implement.
In particular, it requires some way to have backends update a single
global in certain cases, without re-doing semantic analysis. There is
no other part of incremental compilation which requires this.
* Having `@src().line` be comptime-known is useful. For instance, #17688
was justified by broken Tracy integration because the source line
couldn't be comptime-known.
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