bryan-minimal · Jun 27, 2026 · Jun 23, 2026 · Jun 26, 2026 · Jun 26, 2026
@@ -2,10 +2,49 @@
 set -ex
 export CC=gcc
 export LD=gcc
-export RUSTFLAGS="-C linker=gcc --remap-path-prefix=$(pwd)=/builddir --remap-path-prefix=$HOME/.cargo=/cargo -C codegen-units=1"
+# symbol-mangling-version=v0: the default (legacy) mangling appends a hash to
+# each monomorphized generic; for a few instances (Vec::extend_desugared, Vec as
+# Debug/Drop, ...) that hash came out non-deterministic build-to-build. Since
+# rustc places codegen items in symbol-name order, those differing names shuffled
+# addresses and cascaded into a ~10% size-preserving .text/.rela.dyn reordering.
+# v0 mangling is structural (no hash) -> deterministic by construction.
+export RUSTFLAGS="-C linker=gcc --remap-path-prefix=$(pwd)=/builddir --remap-path-prefix=$HOME/.cargo=/cargo -C codegen-units=1 -C symbol-mangling-version=v0"
 export CONST_RANDOM_SEED=0   # pin ahash/const-random compile-time seed
 
-cargo build --release
+# nushell's Cargo.toml [profile.release] sets lto="thin". ThinLTO's parallel
+# backend is non-deterministic — it produces the `.llvm.<hash>` codegen-unit
+# locals and section reordering that left `nu` non-reproducible even WITH
+# `-C codegen-units=1` (LTO runs on top of codegen units, so that flag can't fix
+# it). Override the profile via cargo env (which beats Cargo.toml) to disable LTO;
+# codegen-units=1 then yields deterministic codegen. Modest size/perf cost — the
+# same reproducibility-over-optimization trade as dropping PGO for python.
+export CARGO_PROFIL
7CCB
E_RELEASE_LTO=off
+export CARGO_PROFILE_RELEASE_CODEGEN_UNITS=1
+
+# Determinism shim (fixes a CLASS of Rust non-repro): build-time code — here the
+# pest/pest_consume proc-macros generating the parser — seeds std::HashMap from
+# getrandom(), whose per-process-random seed makes their CODE-GENERATION order vary
+# build-to-build (different Rule discriminants/match-arm order -> different .text).
+# std exposes no knob to pin its hasher, so pin the build's entropy itself: an
+# LD_PRELOAD that makes getrandom/getentropy deterministic, so every build-time
+# HashMap iterates stably. Applies to rustc + all proc-macros for this build only.
+cat > /tmp/detrand.c <<'CEOF'
+#include <stddef.h>
+#include <sys/types.h>
+ssize_t getrandom(void *buf, size_t len, unsigned int flags) {
+    (void)flags;
+    for (size_t i = 0; i < len; i++) ((unsigned char *)buf)[i] = 0;
+    return (ssize_t)len;
+}
+int getentropy(void *buf, size_t len) {
+    for (size_t i = 0; i < len; i++) ((unsigned char *)buf)[i] = 0;
+    return 0;
+}
+CEOF
+gcc -shared -fPIC -O2 -o /tmp/libdetrand.so /tmp/detrand.c
+
+# Scope the shim to the cargo build only — no global export/unset window.
+LD_PRELOAD=/tmp/libdetrand.so cargo build --release
 
 mkdir -p $OUTPUT_DIR/usr/bin
 install -m 755 target/release/nu $OUTPUT_DIR/usr/bin/nu