[sorinirimies]

Stacked on #693 (uses its EnvOverrides); only the last commit is new here. Will rebase once #693 lands.

Summary

RUSTGPU_RUSTFLAGS and RUSTGPU_CARGOFLAGS are split on whitespace, so no flag can contain a space — e.g. --remap-path-prefix=/Users/me/My Projects=/src or a --config value. Cargo solved the same problem for RUSTFLAGS with CARGO_ENCODED_RUSTFLAGS; this mirrors it:

variable	split on	precedence
RUSTGPU_ENCODED_RUSTFLAGS	\x1f	wins over RUSTGPU_RUSTFLAGS
RUSTGPU_ENCODED_CARGOFLAGS	\x1f	wins over RUSTGPU_CARGOFLAGS

Empty encoded value = no flags (as in Cargo). Both new vars emit cargo:rerun-if-env-changed.

RUSTGPU_CODEGEN_ARGS gets no encoded variant: codegen args are passed space-joined in -Cllvm-args=..., so they can't contain spaces anyway.

 EnvOverrides {
-  rustflags:  Option<String>,         // split_whitespace at use site
-  cargoflags: Option<String>,
+  rustflags:  Option<Vec<String>>,    // split_env_flags(ENCODED, plain)
+  cargoflags: Option<Vec<String>>,
 }

Evidence

New tests::env_flags:

unset                                        ok
plain_splits_on_whitespace                   ok
encoded_keeps_spaces_and_takes_precedence    ok
empty_encoded_means_no_flags                 ok

cargo test -p spirv-builder --features watch,clap: 12 passed. Clippy -D warnings clean.

Merge Danger

Door: two-way (new opt-in env vars; easy to remove before a release)

Blast Radius: none unless the new variables are set.