Rust: C-Variadics Land, LTO Gets More Dials

The compiler team stabilized C-variadic function definitions after years on the tracking issue, while a wave of rollups pushed through const-eval hardening and codegen cleanups; separately, two new experimental flags aim to give fat LTO finer-grained control over which crates and partitions get optimized together.

Duration: PT2M44S

Episode overview

This episode is a short developer briefing from Rust.

It explains recent repository work in plain language.

  • Show: Rust
  • Published: 2026-07-23T13:10:30Z
  • Audio duration: PT2M44S

Transcript excerpt

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Good morning. It's July 23rd, and the headline out of the Rust repo is a long-awaited stabilization landing alongside a broad push on link-time optimization tuning.

First, the big one: PR 155697 stabilizes C-variadic function definitions, closing out tracking issue 44930. Folkertdev's work here lets Rust functions accept C-style variable argument lists directly, not just declare them as external. It's a broad change that touched feature gates and library code, and it rode into…

Second theme: const-eval and codegen correctness. RalfJung's PR 159504 makes const-eval queries bail out early when generic types are involved, tightening up validation logic that had been leaning on an undocumented side effect elsewhere. Glandium's PR 157797 complements this on the codegen side, skipping…

Third theme: link-time optimization is getting new knobs. OursCodeur opened two related PRs — 159768 and 159767 — implementing halves of compiler-team proposal 1023. One lets you scope fat LTO to a specific set of crates inside a ThinLTO link; the other splits a fat-LTO module into parallel partitions for faster…

Elsewhere, Kobzol's PR 159451 replaces config cloning in compiletest with a cleaner…

What's…

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