I would be very surprised to see a large Rust codebase being harder to maintain than a large Zig codebase. The former makes it much easier to maintain invariants at scale.
Well, you could go ask Richard Feldman, who I believe cited that reason to rewrite the nascent Roc language from being implemented in Rust to Zig, or anyone else who is moving from Rust to anything else. I've seen multiple people at this point complain about the scaling issue with Rust; the larger the codebase, the more you end up fighting the compiler before anything will actually build.
Note that it doesn't matter if the compiler is correct about its claims; if the language doesn't actively discourage patterns that produce this outcome at scale, then the language does not scale, end of story.
The trend is basically either linear or exponential: as more LOC of Rust are added, the greater the percent of total time you spend fighting the compiler to get a successful build, especially in a team context (which is exactly what gets you to >1M LOC). Solo devs can contain the whole design in their minds and may not run into this issue as much; the problem specifically occurs on teams where the mental model MUST be fractured by necessity, and this results in "distributed knowledge of magic" that ends up constantly breaking.
Perhaps this explains WHY there aren't that many Rust projects done by more than 1 developer that approach that many LOC.
Unless you enforce those macros somehow in a team setting, someone's going to forget to use them, and then you're still stuck with the original problem.
By the time C++ and Java were as old as Rust is today there were thousands of programs that over 1MLOC that had been maintained for at least five years. Rust is a rather old language, yet I doubt there are even hundreds of Rust programs over 1MLOC.
Note that it doesn't matter if the compiler is correct about its claims; if the language doesn't actively discourage patterns that produce this outcome at scale, then the language does not scale, end of story.
The trend is basically either linear or exponential: as more LOC of Rust are added, the greater the percent of total time you spend fighting the compiler to get a successful build, especially in a team context (which is exactly what gets you to >1M LOC). Solo devs can contain the whole design in their minds and may not run into this issue as much; the problem specifically occurs on teams where the mental model MUST be fractured by necessity, and this results in "distributed knowledge of magic" that ends up constantly breaking.
Perhaps this explains WHY there aren't that many Rust projects done by more than 1 developer that approach that many LOC.